The history of HIV is filled with triumphs and failures; living and death. The HIV timeline stretches before us, marking our past and reaching toward out future. But where will that future lead? This HIV/AIDS timeline began early in 1981. In July of that year, the New York Times reported an outbreak of a rare form of cancer among gay men in New York and California. This "gay cancer" as it was called at the time was later identified as Kaposi's Sarcoma, a disease that later became the face of AIDS. About the same time, emergency rooms in New York City began to see a rash of seemingly healthy young men presenting with fevers, flu-like symptoms, and a rare pneumonia called Pneumocystis. This was the beginning of what has become the biggest health care concern in modern history. Twenty-five years later the disease still plagues society.
1959
While we talk about AIDS being 25 years old, in actuality it is believed that the syndrome has been around far longer. In 1959, a man residing in Africa died of a mysterious illness. Only decades later, after examining some blood samples taken from that man, was it confirmed that he actually died from complications related to an HIV infection.
1981
As stated above, 1981 saw the emergence of Kaposi's Sarcoma and Pneumocystis among gay men in New York and California. When the Centers for Disease Control reported the new outbreak they called it "GRID" (gay-related immune deficiency), stigmatizing the gay community as carriers of this deadly disease. However, cases started to be seen in heterosexuals, drug addicts, and people who received blood transfusions, proving the the syndrome knew no boundaries.
1983
Researchers at the Pasteur Institute in France isolate a retrovirus that they believe is related to the outbreak of AIDS. Thirty-three countries around the world have confirmed cases of the disease that was once limited to New York and California. Controversy arises a year later when the US government announces their scientist, Dr. Robert Gallo isolates a retrovirus HTLV-III, that he too claims is responsible for AIDS. Two years later it's confirmed that HTLV-III and the Pasteur retrovirus are indeed the same virus, yet Gallo is still credited with its discovery. An international committee of scientists rename the virus HIV.
1984
A Canadian flight attendant, nicknamed "patient zero" dies of AIDS. Because of his sexual connection to several of the first victims of AIDS, it is believed that he is responsible for introducing the virus into the general population.
8000 confirmed cases in the US
3700 confirmed deaths
1985
The controversy surrounding the HIV virus continues when Robert Gallo's lab patents an HIV test kit that later is approved by the FDA. The Pasteur Institute sues and is later awarded rights to half of the royalties from the new test. At the same time, HIV and AIDS enters the public eye when Rock Hudson dies of AIDS and Ryan White is barred from his elementary school in Indiana.
1987 - A Treatment Arrives
After 6 years of watching people die, a new treatment emerges that is hailed as the first huge step in beating HIV & AIDS. The drug Retrovir (AZT, Zidovudine) is FDA approved and begins to be used in high doses to treat people infected with HIV. And not a minute too soon. Politically, HIV and AIDS is a topic that most avoid. But in response to public pressure, President Ronald Reagan finally acknowledges the HIV problem and for the first time uses the term "AIDS" in a public speech.
100,000 to 150,000 cases of HIV and AIDS
1990
After years of fighting to stay in school, and raging an even harder battle against the ravages of HIV, Ryan White dies at the age of 19. That year, The Ryan White Care Act is enacted by Congress to provide government sponsored funds for the care of HIV infected people.
people living with HIV and AIDS rises to 1 million
1992 - Combination Therapy Arrives
The FDA approves the first drug to be used in combination with AZT. The addition of the drug Hivid marks the beginning of HIV combination therapies. But a more disturbing development centers around HIV tainted blood. Three French senior health officials knowingly sell HIV tainted blood, resulting in the infection of hundreds of transfusion recipients, most of whom have hemophilia.
1993
People who are infected and scientists alike are confused and concerned when a British study, the Concorde Trials, offers proof that AZT monotherapy does nothing to delay progression to AIDS in asymptomatic patients. As a result, the AZT debate emerges, with one side proclaiming AZT saves lives and the other denouncing AZT as useless; the "rethinker" movement is born.
1996 - Protease Inhibitors Arrive
Treatment options take another step forward with the introduction of power HIV-fighting drugs called Protease Inhibitors. The use of these drugs in combination with existing HIV drugs proves effective in controlling HIV. These new "triple-therapies" give patients and scientists new hope in eliminating HIV. But that hope is dashed when a year later, scientists find HIV "hides" in reservoirs in the body, making total elimination of the virus virtually impossible.
1997
In late 1996 data from AIDS Clinical Trials Group study 076 (ACTG 076) made it clear that Retrovir (AZT) used during pregnancy and at the time of delivery drastically reduces transmission of HIV from mother to child. Those findings led to protocols that now drastically reduce transmission from mother to child from 1 in 4 to less than 3%.
1998
More than 15 years after the prediction there would be of an AIDS vaccine within 2 years, the first human trials in the United States of an AIDS vaccine begins. In a desperate attempt to get affordable HIV drugs to the hardest hit areas of Africa, European drug companies ignore US patent laws and begin making generic versions of HIV medications. In response, US drug companies file lawsuits to stop such practices. And sadly, 17 years after AIDS entered our culture, an African AIDS activist is beaten to death by neighbors after publicly admitting she was HIV infected.
2000
The AIDS "rethinker" movement gets international attention and support when South African president Thabo Mbeki questions the use and effectiveness of HIV medications as well as offering doubt that HIV causes AIDS. In response, the international scientific community issues the Durban Declaration, offering proof that HIV and AIDS are indeed connected.
2001
As scientists grow concerned over medication toxicity and effectiveness, US pharmaceutical companies drop their patent lawsuits, paving the way for European drug companies to manufacture and distribute cheaper HIV medications to the hardest hit areas of Sub-Saharan Africa. Cautious optimism emerges with the release of the first entry inhibitor, Fuzeon. Since 1981, 21 million people worldwide have died of AIDS, including 17 million from Sub-Saharan Africa.
31 million people are now living with HIV worldwide, the majority of whom are from African nations
2004
As the emphasis on simpler therapies continues, regimen pill burdens are greatly improved with the release of two new combination drugs, Truvada and Epzicom as well as two new protease inhibitors, Reyataz and Lexiva. In December, the first generic formulation of an HIV medication is approved by the FDA, instilling hope that HIV medication prices may soon come down.
The First Generic HIV Medication
2005
HIV statistics have become sobering to say the least.
4.9 million people were newly infected in 2005
40.3 million people worldwide living with HIV/AIDS.
And as the numbers continue to climb, work on an HIV vaccine has for the most part failed. Once thought to be "just around the corner" it has become obvious in 2005 that an HIV vaccine is still years away. Medication advances continue but long term side effects of HIV medication use are becoming more evident. So much so that experts now agree that for many patients, waiting to start HIV medications is the best course of action. Finally, 2005 saw a rise in HIV rates on college campuses and risky behavior among those people already infected is still a problem. Positive prevention messages are becoming a priority as syphilis and other STD rates of infection continue to rise sharply.
2006
Where are we today? Experts have concluded that HIV has it origins in the jungles of Africa among wild chimps. Experts go on to report that evidence suggests that the simian form of HIV (SIV) entered the human species and became HIV by way of monkey bites or ingesting monkey meat and brains. While the origins of HIV are more clear, the means to pay for HIV care and medications has become more complicated. A revamping of the Medicare / Medicaid systems has made getting medications difficult for many. The United States Congress has yet to reauthorize the largest source of care funding in the US...the Ryan White Care Act. While nobody expects the Act to disappear, it is evident that funding will be cut to almost every program receiving Ryan White Care Act dollars. Yet the epidemic continues. Recently, India surpassed South Africa as the world's largest HIV population and in the US infection rates of HIV are steady while STDs are on the rise. It is obvious that much work needs to be done in the coming years to finally put a halt to the HIV timeline.
Sunday, February 3, 2008
Wednesday, January 2, 2008
Health Education
Health education is "any combination of learning experiences designed to facilitate voluntary actions conducive to health."
Health education is defined as the process by which individuals and groups of people learn to behave in a manner conducive to the promotion, maintenance or restoration of health.
Health education is "any combination of learning experiences designed to facilitate voluntary actions conducive to health."
Health education is defined as the process by which individuals and groups of people learn to behave in a manner conducive to the promotion, maintenance or restoration of health.
Tuesday, January 1, 2008
EPIDEMILOGY OF COMMUNICABLE DISEASES
HIV/AIDS
AIDS is a fatal disease caused by human immunodeficiency virus characterized by profound immunosuppression associated with opportunistic infection, the development of certain tumors (Kaposi’s sarcoma) and frequent involvement of the CNS. Strictly speaking, the term AIDS refers only to the last stage of the HIV infection.
PREVENTION AND CONTROL MEASURES
A. Treatment: There is no specific treatment for HIV/AIDS infection. Certain antiviral drugs are available- Zidovudine, gamma interferon, ribavarin etc.
B. Control: 1. Modification of human behavior regarding
a) Sexual behavior- Avoidance of sexual contact with multiple partners, avoidance of unprotected sexual intercourse, avoidance of high risk activities- anal sex, regular venereological screening for high risk group- prostitutes.
b) Blood transfusion- Screening of donated blood.
c) Contaminated needles and other equipments- Use of disposable syringe and other equipments.
d) Perinatal infection- Infected women of childbearing age should be counseled on avoidance of pregnancy through the use of contraceptives.
2. Counseling of persons found to be antibody positive- Regular medical evaluation and follow up are advised.
3. Health education- To educate the public about the modes of transfusion, to educate the public about safe sex.
C. Surveillance: Collecting and analyzing relevant data about infection in the population, the prevalence and distribution of the infection, the high risk group, patterns of behavior, community attitude to AIDS and the patients.
HIV/AIDS IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• 1st case of HIV detected in 1989.
• Since than total cumulative of 1207 cases of HIV have been confirmed as of 1st December 2007
• 365 have developed AIDS out of whom 123 died
• During 1st December 2007 to 1st December 2007 a total 333 new HIV infection recorded & reported.
• The estimated total number of people living with HIV/AIDS in Bangladesh is around 7,500
• In all 7 rounds of serological surveillance it found that HIV rates have remained below 1% in all ground except in IDUs.
• Among the IDUs prevalence reached from 1.4% in 2000 to 7% in 2006 which is a level closed to concentrated epidemic.
• 7th surveillance shows significant rated of active syphilis among FSWs (1-10%), msm (4-6%) IDUs (1-9%)
HEPATITIS B
Hepatitis B is an acute systemic infection caused by hepatitis B virus which is characterized by long incubation period and which is life threatening. Hepatitis B may occur around the year and it has no seasonal pattern.
High risk group- Surgeons, physician, dentists, nurses, blood bank and hospital personnel, recipients of blood transfusion, homosexuals, prostitutes etc.
PREVENTION AND CONTROL MEASURES
A. Diagnosis: 1. Clinical 2. Lab diagnosis- Immunoassay for HBsAg.
B. Isolation: A patient should be isolated and put on rest.
C. Treatment: No specific treatment for acute or chronic HBV infection, exists although alpha interferon hold some promise.
D. Prevention: 1. Immunization: a) Active- By hepatitis B vaccine. The vaccine consists of HBsAg, each 1 ml dose of the vaccine contains 20 microgram of HBsAg. b) Passive- By hepatitis B immunoglobulin (HBIG). It should be given for immediate protection within 24 hour or almost a week in following circumstances: i) Accidental needle puncture ii) Gross personal contamination with infected blood iii) Newborn infants of carrier mother iv) Sexual contact of acute hepatitis B virus. c) Active-Passive- By simultaneous use of Hepatitis B vaccine and HBIG at separate sites.
2. Specific control measure: i) All person donating blood should be investigated the presence of Hepatitis B virus. ii) Needle, syringe should be properly sterilized before use. iii) Best method is to use disposable syringe and needle. iv) Persons who are at risk(doctors, nurses) all of them should be given HBIG to develop passive immunization.
HEPATITIS B IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• It is indeed scary news that more than 80 per cent of the total demand of blood in Bangladesh comes from professional blood donors, most of whom suffer from various blood-borne diseases like Hepatitis, HIV and Sexually Transmitted Infections (STIs).
• According to World Health Organization (WHO), transfusion-transmitted infections (TTIs) remains a major public health problem in the country as the demand for blood transfusions is mostly met by unscreened contaminated blood collected from professional donors on payment.
• Poverty, poorly managed commercial blood banks (less sensitive screening and lack of quality control) and an increasing trend in drug addiction and prostitution are listed as the main causes of the prevalence hepatitis B virus (HBV) in professional donors. In 2001 WHO ranked Bangladesh in the moderate-to high-risk group of countries for HBV infection.
MEASLES
Measles is an acute inflammatory disease caused by a paramyxovirus which presents with respiratory catarrhal symptoms (fever, Koplik’s spots on buccal mucosa) and a characteristic skin rash. Maternal antibody gives protection for the first 6 months of life. Measles is a serious disease in the malnourished, vitamin deficient or immunocompromised.
PREVENTION AND CONTROL MEASURES
A. Diagnosis: Clinical: 1. Prodromal phase (Catarrhal stage): This is characterized by- Fever, Sneezing, Conjunctivitis, Coughing, Hoarseness of voice, Koplik’s spots- bright red lesions with a white, central spot that are located on the buccal mucosa and are virtually diagnostic of measles. They last for 3 or 4 days. 2. Exanthematous stage: This stage is characterized by- Dark red macular or maculopapular rash- It develops first at the back of the ears and at the junction of the forehead and the hair. Within a few hours the rash proceeds gradually down the body to the lower extremities.
Laboratory Diagnosis: a) Blood count- Leukocytosis in the early stages followed by an increase in lymphocytes. b) Sputum or urine culture- Stained smears show large multinucleate (giant) cells.
B. Isolation: All patients should be isolated for 10 days from the appearance of the rash.
C. Treatment: Antiviral therapy- Not available. Antibiotics- It should be given only if a
child has clinical signs of pneumonia or other evidence of sepsis.
D. Prevention: i) Active immunization- A children should be protected by measles intramuscularly or subcutaneously at deltoid region. ii) Passive immunization- with human gamma globulin 0.25 mg/kg is effective if given within 3 days of exposure.
MEASLES IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• In 1984 before EPI intensification 2.6 million children suffered from measles
• In 1999 number of cases dropped to 1 million
• In 2003 no of measles cases were 4505
• In 2004 no of measles cases were 10090
• In 2005 no of measles cases were 28370
• In 2007 no of measles outbreaks were 292
• Around 20,000 children died from measles complication every year until 2005.
• Measles immunization coverage is also poor which was 78% in 2006
• Global Death of Measles fell by 48% from 1999 to 2004
• Deaths reduced from 8.7 million in 1999 to 4.5 million in 2004
• 4.1 million are children out of 4.5 million died
• >95% of Measles death occurred in countries having GNI less than $1000
• 47 Countries account for about 98% of global measles deaths
HOOKWORM INFECTION
Hookworm infection is a chronic debilitating disease caused by soil transmitted helminthes A. duodenale and N. americanus, clinically characterized by anemia (microcytic hypochromic). It is more common in the countries of low socio-economic status where disposal of excreta is not sanitary. A. duodenale infection is common in Bangladesh.
PREVENTION AND CONTROL MEASURES
A. Diagnosis: 1. Clinical 2. Laboratory- a) Finding of hookworm eggs in feces b) Occult blood test- should be positive c) Blood test for anemia
B. Control: Control of hookworm infection involves 4 approaches- 1. Sanitary disposal of feces 2. Health education with community participation 3. Chemotherapy 4. Correction of anemia.
1. Sanitation and health education-
• The provision of latrine and education in their proper usage are crucial to the control of hookworm infection.
• Fecal contamination of soil must be prevented.
• Wearing of shoes to protect the feet
• Wearing of hand gloves when handling suspected things polluted with the hookworm larvae.
2. Chemotherapy-
a) Treatment strategy- Mass treatment of whole community selective chemotherapy of all those infected.
b) Drugs-
• Tab. Mebendazol (100 mg) twice daily for 3 days. Most effective for the treatment of hookworm infection.
• Tab. Albendazol (400 mg) in a single dose for all ages over 1 yr.
• Tab. Pyrantel (10 mg/kg) in a single dose for 3 days.
3. Correction of anemia- Ferrous sulphate (200 mg) thrice daily by mouth for 3 months till hemoglobin concentration has risen to 12g /100 ml.
HOOKWORM INFECTION IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• The latest evidence confirms that blood loss caused by the worms' feeding activity in the gut is a contributing factor in the development of poor iron status leading to iron-deficiency anemia.
• The World Health Organization has identified adolescent girls and women of child-bearing age as high-risk groups regarding the impact of hookworm disease.
• Treating pregnant women with anthelminthic drugs after the first trimester is very much useful to prevent future sufferings from iron deficiency anemia.
CHOLERA
Cholera is an acute diarrheal disease caused by V. cholerae classically characterized by sudden onset of profuse, effortless, watery diarrhea followed by vomiting, marked dehydration, muscular cramps and suppression of urine.
PREVENTION AND CONTROL MEASURES
A. Notification- Cholera is an internationally notifiable disease.
B. Diagnosis: i) Clinical diagnosis ii) Lab diagnosis: a. M/E of Stool- under DGI will show shooting star appearance b. Culture of the Stool
C. Isolation: All cases should be isolated in ICDDRB until at least 3 culture examination are negative.
D. Disinfection: All contaminated articles disinfected by phenols, boiling or lime.
E. Treatment: 1. Rehydration therapy: Prevention and management of dehydration-home-based fluids, ORS, IV fluids. Continued feeding. 2. Drug Treatment: Use of an effective antimicrobial drug e.g. Doxycycline, Erythromycin, Azithromycin, Newer quinolones (Cipro, Norflox) etc.
F. Prevention:
1. Personal prophylaxis and public health measures:
a. Improved sanitation- Provision of safe drinking water, satisfactory sanitary disposal of excreta, refuse & sewage, protection of Foods, house fly control measures.
b. Health education: To drink safe water from tube well, otherwise boiled water or tablet treated water, avoid hot & rotten food and raw vegetables, good hygiene should be maintained.
2. Chemoprophylaxis: Mass treatment with Tetracycline.
3. Vaccination: Cholera vaccine 50% effective in preventing disease for 3-6 months.
CHOLERA IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• Lack of safe drinking water and inadequate safe drinking water supply system.
• High density of population
• Unsatisfactory unhygienic disposal of excreta and refuse
• Cholera is endemic in Bangladesh with periodic epidemic outbreaks- does not report to WHO.
• V. cholerae infection causes the most severe form of secretory diarrheas.
• New serotype V. cholerae O139
• ICDDR,B hosts the only hospital by the name “CHOLERA HOSPITAL” that treats about 1 million diarrheal patients per year.
• About 30% of them are adults.
• During the epidemic situation more than 50% of the adults suffer from cholera.
• Can be fatal if left untreated.
• 10% develop typical severe cholera
• Case fatality: <1%>
AIDS is a fatal disease caused by human immunodeficiency virus characterized by profound immunosuppression associated with opportunistic infection, the development of certain tumors (Kaposi’s sarcoma) and frequent involvement of the CNS. Strictly speaking, the term AIDS refers only to the last stage of the HIV infection.
PREVENTION AND CONTROL MEASURES
A. Treatment: There is no specific treatment for HIV/AIDS infection. Certain antiviral drugs are available- Zidovudine, gamma interferon, ribavarin etc.
B. Control: 1. Modification of human behavior regarding
a) Sexual behavior- Avoidance of sexual contact with multiple partners, avoidance of unprotected sexual intercourse, avoidance of high risk activities- anal sex, regular venereological screening for high risk group- prostitutes.
b) Blood transfusion- Screening of donated blood.
c) Contaminated needles and other equipments- Use of disposable syringe and other equipments.
d) Perinatal infection- Infected women of childbearing age should be counseled on avoidance of pregnancy through the use of contraceptives.
2. Counseling of persons found to be antibody positive- Regular medical evaluation and follow up are advised.
3. Health education- To educate the public about the modes of transfusion, to educate the public about safe sex.
C. Surveillance: Collecting and analyzing relevant data about infection in the population, the prevalence and distribution of the infection, the high risk group, patterns of behavior, community attitude to AIDS and the patients.
HIV/AIDS IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• 1st case of HIV detected in 1989.
• Since than total cumulative of 1207 cases of HIV have been confirmed as of 1st December 2007
• 365 have developed AIDS out of whom 123 died
• During 1st December 2007 to 1st December 2007 a total 333 new HIV infection recorded & reported.
• The estimated total number of people living with HIV/AIDS in Bangladesh is around 7,500
• In all 7 rounds of serological surveillance it found that HIV rates have remained below 1% in all ground except in IDUs.
• Among the IDUs prevalence reached from 1.4% in 2000 to 7% in 2006 which is a level closed to concentrated epidemic.
• 7th surveillance shows significant rated of active syphilis among FSWs (1-10%), msm (4-6%) IDUs (1-9%)
HEPATITIS B
Hepatitis B is an acute systemic infection caused by hepatitis B virus which is characterized by long incubation period and which is life threatening. Hepatitis B may occur around the year and it has no seasonal pattern.
High risk group- Surgeons, physician, dentists, nurses, blood bank and hospital personnel, recipients of blood transfusion, homosexuals, prostitutes etc.
PREVENTION AND CONTROL MEASURES
A. Diagnosis: 1. Clinical 2. Lab diagnosis- Immunoassay for HBsAg.
B. Isolation: A patient should be isolated and put on rest.
C. Treatment: No specific treatment for acute or chronic HBV infection, exists although alpha interferon hold some promise.
D. Prevention: 1. Immunization: a) Active- By hepatitis B vaccine. The vaccine consists of HBsAg, each 1 ml dose of the vaccine contains 20 microgram of HBsAg. b) Passive- By hepatitis B immunoglobulin (HBIG). It should be given for immediate protection within 24 hour or almost a week in following circumstances: i) Accidental needle puncture ii) Gross personal contamination with infected blood iii) Newborn infants of carrier mother iv) Sexual contact of acute hepatitis B virus. c) Active-Passive- By simultaneous use of Hepatitis B vaccine and HBIG at separate sites.
2. Specific control measure: i) All person donating blood should be investigated the presence of Hepatitis B virus. ii) Needle, syringe should be properly sterilized before use. iii) Best method is to use disposable syringe and needle. iv) Persons who are at risk(doctors, nurses) all of them should be given HBIG to develop passive immunization.
HEPATITIS B IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• It is indeed scary news that more than 80 per cent of the total demand of blood in Bangladesh comes from professional blood donors, most of whom suffer from various blood-borne diseases like Hepatitis, HIV and Sexually Transmitted Infections (STIs).
• According to World Health Organization (WHO), transfusion-transmitted infections (TTIs) remains a major public health problem in the country as the demand for blood transfusions is mostly met by unscreened contaminated blood collected from professional donors on payment.
• Poverty, poorly managed commercial blood banks (less sensitive screening and lack of quality control) and an increasing trend in drug addiction and prostitution are listed as the main causes of the prevalence hepatitis B virus (HBV) in professional donors. In 2001 WHO ranked Bangladesh in the moderate-to high-risk group of countries for HBV infection.
MEASLES
Measles is an acute inflammatory disease caused by a paramyxovirus which presents with respiratory catarrhal symptoms (fever, Koplik’s spots on buccal mucosa) and a characteristic skin rash. Maternal antibody gives protection for the first 6 months of life. Measles is a serious disease in the malnourished, vitamin deficient or immunocompromised.
PREVENTION AND CONTROL MEASURES
A. Diagnosis: Clinical: 1. Prodromal phase (Catarrhal stage): This is characterized by- Fever, Sneezing, Conjunctivitis, Coughing, Hoarseness of voice, Koplik’s spots- bright red lesions with a white, central spot that are located on the buccal mucosa and are virtually diagnostic of measles. They last for 3 or 4 days. 2. Exanthematous stage: This stage is characterized by- Dark red macular or maculopapular rash- It develops first at the back of the ears and at the junction of the forehead and the hair. Within a few hours the rash proceeds gradually down the body to the lower extremities.
Laboratory Diagnosis: a) Blood count- Leukocytosis in the early stages followed by an increase in lymphocytes. b) Sputum or urine culture- Stained smears show large multinucleate (giant) cells.
B. Isolation: All patients should be isolated for 10 days from the appearance of the rash.
C. Treatment: Antiviral therapy- Not available. Antibiotics- It should be given only if a
child has clinical signs of pneumonia or other evidence of sepsis.
D. Prevention: i) Active immunization- A children should be protected by measles intramuscularly or subcutaneously at deltoid region. ii) Passive immunization- with human gamma globulin 0.25 mg/kg is effective if given within 3 days of exposure.
MEASLES IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• In 1984 before EPI intensification 2.6 million children suffered from measles
• In 1999 number of cases dropped to 1 million
• In 2003 no of measles cases were 4505
• In 2004 no of measles cases were 10090
• In 2005 no of measles cases were 28370
• In 2007 no of measles outbreaks were 292
• Around 20,000 children died from measles complication every year until 2005.
• Measles immunization coverage is also poor which was 78% in 2006
• Global Death of Measles fell by 48% from 1999 to 2004
• Deaths reduced from 8.7 million in 1999 to 4.5 million in 2004
• 4.1 million are children out of 4.5 million died
• >95% of Measles death occurred in countries having GNI less than $1000
• 47 Countries account for about 98% of global measles deaths
HOOKWORM INFECTION
Hookworm infection is a chronic debilitating disease caused by soil transmitted helminthes A. duodenale and N. americanus, clinically characterized by anemia (microcytic hypochromic). It is more common in the countries of low socio-economic status where disposal of excreta is not sanitary. A. duodenale infection is common in Bangladesh.
PREVENTION AND CONTROL MEASURES
A. Diagnosis: 1. Clinical 2. Laboratory- a) Finding of hookworm eggs in feces b) Occult blood test- should be positive c) Blood test for anemia
B. Control: Control of hookworm infection involves 4 approaches- 1. Sanitary disposal of feces 2. Health education with community participation 3. Chemotherapy 4. Correction of anemia.
1. Sanitation and health education-
• The provision of latrine and education in their proper usage are crucial to the control of hookworm infection.
• Fecal contamination of soil must be prevented.
• Wearing of shoes to protect the feet
• Wearing of hand gloves when handling suspected things polluted with the hookworm larvae.
2. Chemotherapy-
a) Treatment strategy- Mass treatment of whole community selective chemotherapy of all those infected.
b) Drugs-
• Tab. Mebendazol (100 mg) twice daily for 3 days. Most effective for the treatment of hookworm infection.
• Tab. Albendazol (400 mg) in a single dose for all ages over 1 yr.
• Tab. Pyrantel (10 mg/kg) in a single dose for 3 days.
3. Correction of anemia- Ferrous sulphate (200 mg) thrice daily by mouth for 3 months till hemoglobin concentration has risen to 12g /100 ml.
HOOKWORM INFECTION IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• The latest evidence confirms that blood loss caused by the worms' feeding activity in the gut is a contributing factor in the development of poor iron status leading to iron-deficiency anemia.
• The World Health Organization has identified adolescent girls and women of child-bearing age as high-risk groups regarding the impact of hookworm disease.
• Treating pregnant women with anthelminthic drugs after the first trimester is very much useful to prevent future sufferings from iron deficiency anemia.
CHOLERA
Cholera is an acute diarrheal disease caused by V. cholerae classically characterized by sudden onset of profuse, effortless, watery diarrhea followed by vomiting, marked dehydration, muscular cramps and suppression of urine.
PREVENTION AND CONTROL MEASURES
A. Notification- Cholera is an internationally notifiable disease.
B. Diagnosis: i) Clinical diagnosis ii) Lab diagnosis: a. M/E of Stool- under DGI will show shooting star appearance b. Culture of the Stool
C. Isolation: All cases should be isolated in ICDDRB until at least 3 culture examination are negative.
D. Disinfection: All contaminated articles disinfected by phenols, boiling or lime.
E. Treatment: 1. Rehydration therapy: Prevention and management of dehydration-home-based fluids, ORS, IV fluids. Continued feeding. 2. Drug Treatment: Use of an effective antimicrobial drug e.g. Doxycycline, Erythromycin, Azithromycin, Newer quinolones (Cipro, Norflox) etc.
F. Prevention:
1. Personal prophylaxis and public health measures:
a. Improved sanitation- Provision of safe drinking water, satisfactory sanitary disposal of excreta, refuse & sewage, protection of Foods, house fly control measures.
b. Health education: To drink safe water from tube well, otherwise boiled water or tablet treated water, avoid hot & rotten food and raw vegetables, good hygiene should be maintained.
2. Chemoprophylaxis: Mass treatment with Tetracycline.
3. Vaccination: Cholera vaccine 50% effective in preventing disease for 3-6 months.
CHOLERA IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• Lack of safe drinking water and inadequate safe drinking water supply system.
• High density of population
• Unsatisfactory unhygienic disposal of excreta and refuse
• Cholera is endemic in Bangladesh with periodic epidemic outbreaks- does not report to WHO.
• V. cholerae infection causes the most severe form of secretory diarrheas.
• New serotype V. cholerae O139
• ICDDR,B hosts the only hospital by the name “CHOLERA HOSPITAL” that treats about 1 million diarrheal patients per year.
• About 30% of them are adults.
• During the epidemic situation more than 50% of the adults suffer from cholera.
• Can be fatal if left untreated.
• 10% develop typical severe cholera
• Case fatality: <1%>
• Can kill an adult in 2-4 hours
MALARIA
Malaria is a disease of wide distribution caused by sporozoa of the genus plasmodium characterized by paroxysmal fever with periods of latency, enlargement of spleen and secondary anaemia.
There are 4 species of malarial parasites which infect humans:
• P. falciparum. This species, predominant in Africa, produces the most severe symptoms and is responsible for most malaria deaths.
• P. vivax. This species, found mostly in tropical areas of Asia, produces less severe symptoms but can remain in your liver and cause relapses for up to three years.
• P. malariae. This species found in Africa, can cause typical malaria symptoms, but on rare occasions it can remain in bloodstream.
• P. ovale. This species is found mostly in West Africa. Although rare, it can also cause relapses.
PREVENTION AND CONTROL MEASURES
A. The individual: Chemoprophylaxis: the antimalarial available for chemoprophylaxis are proguanil, Chloroquine, Maloprim, Mefloquine.
B. The Vector: attempted in two ways- 1. Adult mosquito Control: by insecticides varies from area to area. 2. Prevention of mosquito breeding by larval control: heavy oiling with antimalarial oil &insecticides, spraying with 5 % DDT.
C. The community: Active community participation is important. The measures to be applied by locally recruited and trained workers include- residual spraying, larviciding, mass drug administration.
D. Prevention:
• There's no effective vaccine against malaria.
• In countries where the disease is endemic, prevention involves keeping mosquitoes away from humans. This has included the use of insecticide-treated mosquito netting and spraying indoor walls with insecticide.
• Most drugs used to treat malaria are also used to prevent it. Doctors sometimes use the antibiotic doxycycline to prevent malaria. Tips to prevent malaria: The CDC also recommends the following measures to help prevent malaria:
• Use repellent. Spray DEET insect repellent on exposed skin, and use flying-insect spray to kill mosquitoes in your sleeping area. • Wear protective clothing. During active mosquito times, usually from dusk to dawn, wear pants and long-sleeved shirts. • Use netting. If you're staying in a place that doesn't have screens or air conditioning, sleep under mosquito netting that's been treated with an insecticide called permethrin. This netting is available in many travel and camping supply stores and online.
MALARIA IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• In Bangladesh, it is mainly caused by the female Anopheles mosquitoes.
• The disease restricted to areas where the females Anopheles mosquitoes can bread.
• Malaria is now on the increase due to emergence of drug resistance.
• Presence of extra human reservoir of infection.
• Common border of Bangladesh & India: disease agent can cross the border & cause malaria of the people of the border area.
• Hilly areas are covered with dense forest where operation could not carried out properly.
• Migratory habit of the people
• Poor standard of environmental sanitation.
TYPHOID FEVER
Typhoid is an infectious and communicable disease caused by gram negative bacillus Salmonella typhi, characterized by headache, high fever, malaise, anorexia, abdominal discomfort and pt. is very much toxic. The disease is also known as Enteric fever - as because, it affects gastrointestinal tract. The disease also affects Liver, Kidneys, Lungs, Heart, and Lymph nodes & Glands.
PREVENTION AND CONTROL MEASURES
A. Notification
B. Diagnosis: i) Clinical ii) Laboratory- a. Blood culture: in MacConkey’s agar media- Positive at 1st week b. Stool culture: in MacConkey’s agar media, DCA-Positive from 2nd or 3rd week c. Urine culture: in MacConkey’s agar media- Positive in 2nd, 3rd or 4th week d. Serological test: Widal test - Positive during 2nd week e. Phage typing of isolated strains f. Routine blood test: TC - Leucopenia, DC - Neutropenia
C. Isolation: Case should be isolated till “3” negative stools and urine culture reports are obtained on three separate days.
D. Disinfection: Stools and urine should be disinfected with 5% cresol.
E. Treatment: Ciprofloxacin is now a days the drug of choice.
F. Follow-up: Stool and Urine examination should be done for detection of S. typhi, 3 to 4 months after discharge of the patient.
G. Prevention: 1. Community measure: Ensure Safe water supply, ensure safety food, proper disposal of human excreta and garbage, health education. 2. Immunization: a. Ty21a Vaccine(Vivotif Berna, Swiss Serum and Vaccine Institute) 1 capsule by mouth 4 doses @ 2 days alternate b. ViCPS (Typhim Vi, Pasteur Merieux) Injection single dose
TYPHOID IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• Typhoid fever is very common in Bangladesh, where this pathogen thrives in areas where disasters have compromised sanitation with the typical tropic zone.
• Preliminary results from recent studies conducted in Bangladesh by ICDDR,B show an incidence of approximately 2000 per 100 000 per year.
• Typhoid is a curable as well as preventable disease, and socio-economic impact is huge, so it is in consideration and concern of public health.
• Typhoid fever is common in Bangladesh because water supplies and sanitation are sub-standard.
TUBERCULOSIS
Tuberculosis is a chronic infectious and communicable infectious disease caused by Mycobacterium tuberculosis. This disease primarily affects lungs but it may affect other organs also e.g. Intestines, Bones, Joints, Lymph glands and others.
PREVENTION AND CONTROL MEASURES
The control of tuberculosis can be considered at the six levels of prevention:
A. General health promotion: Adequate housing, good nutrition, health education.
B. Active immunization: By BCG (Bacille Calmette Guerin) vaccine at birth in a single dose (0.1 ml) intradermally which is a live attenuated vaccine.
C. Early diagnosis and treatment: 1. Screening- Tuberculin test, Staining of sputum, Chest X-ray. 2. Isolation- Patient should preferably be isolated from young children. 3. Drug treatment: The overall goal for treatment of tuberculosis- a. To cure the individual patient b. To minimize the transmission of Mycobacterium tuberculosis to other persons. The anti tubercular drugs are- Isoniazid, Rifampicin, Pyrazinamide, Ethambutol, and Streptomycin. • Regimen for new smear-positive patients and other severely ill patients: 2HRZE/4H3R3 • Regimen for relapses and failures: 2SHRZE/1REHZ/5R3E3H3 • Regimen for smear-negative and extra-pulmonary patients: 2HRZ/4H3R3
D. Rehabilitation
E. Surveillance: The source of data will include- Notification of cases, post mortem reports, record of BCG immunization, housing- data about overcrowding. F. Control strategy: Tuberculosis control means reduction in the prevalence and incidence of disease in the community. DOTS is a control strategy which ensures - • Sustained Political Commitment • Case Detection through Quality assured Sputum microscopy • Uninterrupted supply of Drugs • Standardized treatment regimen • Standardized recording and reporting system
TUBERCULOSIS IS A PUBLIC HEALTH PROBLEM IN BANGLADESH
• Tuberculosis is a major public health problem in Bangladesh. In 2006, World Health Organization (WHO) ranked Bangladesh 6th among the world's 22 high-burden TB countries.
• In Bangladesh, More than 319,000 new cases, including 143,000 sputum smear-positive (SS+) pulmonary TB cases and 70,000 TB-related deaths occur annually.
• WHO declared TB as a global emergency and recommended DOTS strategy. Bangladesh introduced this strategy in 1993 and it is expanded all upazilas by 1998.
Sample Size and its Determination
Sample Size Determination
In sampling analysis the most ticklish questions: What should be the size of the sample or how large or small should be (‘n’)? If the sample size (‘n’) is too small, it may not serve to achieve the objectives and if it is too large, we may incur huge cost and waste resources. As a general rule, one can say that the sample must be of an optimum size I.e. it should neither be excessively large nor too small. Technically, the sample size should be large enough to give a confidence interval of desired width and as such the size of the sample must be chosen by some logical process before sample is taken from the universe. Size of the sample should be determined by researcher keeping in view the following points:
(i) Nature of universe:
Universe may be either homogenous or heterogeneous in nature. If the items of the universe are homogenous, a small sample can serve the purpose. But if the items are heterogeneous, a large sample would be required. Technically, this can be termed as the dispersion factor.
(ii) Number of classes proposed:
If many class-groups (groups and sub-groups) are to be formed, a large sample would be required because a small sample might not be able to give a reasonable number of items in each class-group.
(iii)Nature of study:
If items are to be intensively and continuously studied, the sample should be small. For a general survey the size of the sample should be large, but a small sample 9s considered appropriate in technical survey.
(iv)Type of sampling:
Sampling technique plays an important part in determining the size of the sample. A small random sample is apt to be much superior to a larger but badly selected sample.
(v) Standard of accuracy and acceptable confidence level:
If the standard of accuracy or the level of precision is to be kept high, we shall require relatively larger sample. For doubling the accuracy for a fixed significance level, the sample size has to be increased fourfold.
(vi) Availability of finance:
In practice, size of the sample depends upon the amount of money available for the study purposes. This factor should be kept in view while determining the the size of sample for large samples result in increasing the cost of sampling estimates.
(vii) Other considerations:
Nature of units, size of the population, size of questionnaire, availability of trained investigators, the conditions under which the sample is being conducted, the time available for completion of the study are a few other considerations to which a researcher must pay attention while selecting the size of the sample.
There are two alternative approaches for determining the size of the sample. The first approach is “ to specify the precision of estimation desired and then to determine the sample size necessary to insure it” and the second approach “uses Bayesian statistics to weigh the cost of additional information against the expected value of the additional information”. The first approach is capable of giving a mathematical solution, and as such is a frequently used technique of determining ‘n’. The limitation of this technique is that it does not analyze the sot of gathering information vis-à-vis the expected value of information. The second approach is theoretically optimal, but it is seldom used because of the difficulty involved in measuring the value of information. Hence, we shall mainly concentrate here on the first approach.
Health And Disease
Health
• Health is a state of complete physical, mental, social and spiritual well-being and not merely the absence of disease or infirmity in all matter.
• Spiritual - quality of courage, vigor, liveliness
• Vigor - Mental or physical energy
• Infirmity - Weakness.
• From the definition of health the following dimensions can be inferred:
• Dictionary meaning of Disease is ‘no comfort’; dis means ‘away from’; ease means comfort; therefore, disease means away from comfort, or no comfort. In other words, disease is the general term for deviation from health. Therefore, disease is a condition or state of health where there is a chance that the body and mind may function abnormally. Dr. Badrul Alam (2001) states in his article, ‘Better use of medicine’ that disorder of ease abbreviates itself into the word” disease” and when that uneasiness of self compels the person to behave abnormally he feels he is sick. When the signs and symptoms are manifested and the person seeks the help of the doctors he diagnoses him as a sick person and labels his disease condition. He further adds that medicine and disease should have a close relation. Like disease, medicine can cause disorders in the body economy such as untoward symptoms, side effects, abnormal reactions etc. This is why medicine is to be used to kill disease.
• “Metaphorically speaking, disease is resistance.
• Disease manifested by symptoms, expresses the vital reaction and resistance of the living organism to the inroads of some injurious agent for influence. It is a battle, a struggle, a costly and painfully resistance to an invader
• Health is a state of complete physical, mental, social and spiritual well-being and not merely the absence of disease or infirmity in all matter.
• Spiritual - quality of courage, vigor, liveliness
• Vigor - Mental or physical energy
• Infirmity - Weakness.
• From the definition of health the following dimensions can be inferred:
- Freedom from pain-and a physical sense of well being.
- Freedom from extremes of emotion- and a sense of dynamic calmness.
- Freedom from confusion- and a sense of mental clarity.
- A sense of being part of the whole cosmos; a spiritual sense of purpose in life and a feeling of inner fulfillment.
- Equilibrium and adaptability and ease on all levels (Hence, the word disease) and hence “glowing and flowing”.
- Fully functioning-according to one’s ability
- Living life to the full-according to one’s unique gifts.
- In summary, health is the physiological condition of a person. Any deviation from this physiology may be termed as disease condition or pathology.
• Dictionary meaning of Disease is ‘no comfort’; dis means ‘away from’; ease means comfort; therefore, disease means away from comfort, or no comfort. In other words, disease is the general term for deviation from health. Therefore, disease is a condition or state of health where there is a chance that the body and mind may function abnormally. Dr. Badrul Alam (2001) states in his article, ‘Better use of medicine’ that disorder of ease abbreviates itself into the word” disease” and when that uneasiness of self compels the person to behave abnormally he feels he is sick. When the signs and symptoms are manifested and the person seeks the help of the doctors he diagnoses him as a sick person and labels his disease condition. He further adds that medicine and disease should have a close relation. Like disease, medicine can cause disorders in the body economy such as untoward symptoms, side effects, abnormal reactions etc. This is why medicine is to be used to kill disease.
• “Metaphorically speaking, disease is resistance.
• Disease manifested by symptoms, expresses the vital reaction and resistance of the living organism to the inroads of some injurious agent for influence. It is a battle, a struggle, a costly and painfully resistance to an invader
BURNING ISSUES OF PUBLIC HEALTH IN BANGLADESH
Bangladesh is a densely populated country. Masses of people in Bangladesh face a perilous situation due to hazardous health conditions in the country. The main source of these conditions is the poverty and backwardness maintained and deepened by capitalist rule. As a result serious health problems became a burden to this country. Major health problems, which became concerning issues for the public health management of this country, are given below-
PUBLIC HEALTH HAZARDS IN BANGLADESH-
• COMMUNICABLE DISEASE PROBLEM-
Malaria, Filariasis, TB, Leprosy, Diarrhoel Disease, Cholera, Acute Respiratory Infection (ARI), Acquired Immune Deficiency Syndrome (AIDS)
• NUTRIONAL PROBLEMS-
Protein Energy Malnutrition (PEM), Low Birth Weight, Nutritional Anemia (Iron deficiency), Nutritional Blindness (Xeropthalamia), Iodine Deficiency Disorder (IDD), Neurolathyrism, Endemic Flurosis.
• ENVIRONMENTAL SANITATION PROBLEM-
Lack of safe water supply, Lack of sanitary disposal of refuse, Sewage &
Excreta, Noise & air pollution, Lack of quality good food & consumer
Products.
• MEDICAL CARE PROBLEM-
Inadequate financial resources, health manpower and health infrastructure, uneven distribution of health personnel/doctors, more in urban areas, overcrowding in hospitals due to migration from rural to urban.
• POPULATION PROBLEM-
This is related to all aspects of development especially in Employment,
Education, Environment, Housing, Health care, Sanitation, Family planning.
Population explosion.
• SOCIAL PROBLEMS –
Alcoholism, Drug dependence, Sexually transmitted disease, Prostitution, Dowry system.
PUBLIC HEALTH HAZARDS IN BANGLADESH-
• COMMUNICABLE DISEASE PROBLEM-
Malaria, Filariasis, TB, Leprosy, Diarrhoel Disease, Cholera, Acute Respiratory Infection (ARI), Acquired Immune Deficiency Syndrome (AIDS)
• NUTRIONAL PROBLEMS-
Protein Energy Malnutrition (PEM), Low Birth Weight, Nutritional Anemia (Iron deficiency), Nutritional Blindness (Xeropthalamia), Iodine Deficiency Disorder (IDD), Neurolathyrism, Endemic Flurosis.
• ENVIRONMENTAL SANITATION PROBLEM-
Lack of safe water supply, Lack of sanitary disposal of refuse, Sewage &
Excreta, Noise & air pollution, Lack of quality good food & consumer
Products.
• MEDICAL CARE PROBLEM-
Inadequate financial resources, health manpower and health infrastructure, uneven distribution of health personnel/doctors, more in urban areas, overcrowding in hospitals due to migration from rural to urban.
• POPULATION PROBLEM-
This is related to all aspects of development especially in Employment,
Education, Environment, Housing, Health care, Sanitation, Family planning.
Population explosion.
• SOCIAL PROBLEMS –
Alcoholism, Drug dependence, Sexually transmitted disease, Prostitution, Dowry system.
BIAS AND CONFOUNDING
HYPOTHESIS FORMULATION AND ERRORS IN RESEARCH
All analytic studies must begin with a clearly formulated hypothesis. The hypothesis must be quantitative and specific. It must predict a relationship of a specific size.
For example:
“Babies who are breast-fed have less illness than babies who are bottle-fed.”
Which illnesses? How is feeding type defined? How large a difference in risk?
A better example:
“Babies who are exclusively breast-fed for three months or more will have a reduction in the incidence of hospital admissions for gastroenteritis of at least 30% over the first year of life.”
Only specific prediction allows one to draw legitimate conclusions from a study which tests a hypothesis. But even with the best formulated hypothesis, two types of errors can occur.
• Type 1 - observing a difference when in truth there is none.
• Type 2 - failing to observe a difference when there is one.
These errors are generally produced by one or more of the following:
• RANDOM ERROR
• RANDOM MISCLASSIFICATION
• BIAS
• CONFOUNDING
RANDOM ERROR :
Deviation of results and inferences from the truth, occurring only as a result of the operation of chance. Can produce type 1 or type 2 errors.
RANDOM (OR NON-DIFFERENTIAL) MISCLASSIFICATION :
Random error applied to the measurement of an exposure or outcome. Errors in classification can only produce type 2 errors, except if applied to a confounder or to an exposure gradient.
BIAS:
Systematic, non-random deviation of results and inferences from the truth, or processes leading to such deviation. Any trend in the collection, analysis, interpretation, publication or review of data that can lead to conclusions which are systematically different from the truth.
Note that in bias, the focus is on an artifact of some part of the research process (assembling subjects, collecting data, analyzing data) that produces a spurious result. Bias can produce either a type 1 or a type 2 error, but we usually focus on type 1 errors due to bias.
Bias can be either conscious or unconscious. In epidemiology, the word bias does not imply, as in common usage, prejudice or deliberate deviation from the truth.
CONFOUNDING :
A problem resulting from the fact that one feature of study subjects has not been separated from a second feature, and has thus been confounded with it, producing a spurious result. The spuriousness arises from the effect of the first feature being mistakenly attributed to the second feature. Confounding can produce either a type 1 or a type 2 error, but we usually focus on type 1 errors.
THE DIFFERENCE BETWEEN BIAS AND CONFOUNDING:
Bias creates an association that is not true, but confounding describes an association that is true, but potentially misleading.
EXAMPLES OF RANDOM ERROR, BIAS, MISCLASSIFICATION AND CONFOUNDING IN THE SAME STUDY:
STUDY: In a cohort study, babies of women who bottle feed and women who breast feed are compared, and it is found that the incidence of gastroenteritis, as recorded in medical records, is lower in the babies who are breast-fed.
EXAMPLE OF RANDOM ERROR :
By chance, there are more episodes of gastroenteritis in the bottle-fed group in the study sample, producing a type 1 error. (When in truth breast feeding is not protective against gastroenteritis).
Or, also by chance, no difference in risk was found, producing a type 2 error (When in truth breast feeding is protective against gastroenteritis).
EXAMPLE OF RANDOM MISCLASSIFICATION :
Lack of good information on feeding history results in some breast-feeding mothers being randomly classified as bottle-feeding, and vice-versa. If this happens, the study finding underestimates the true RR, whichever feeding modality is associated with higher disease incidence, producing a type 2 error.
EXAMPLE OF BIAS:
The medical records of bottle-fed babies only are less complete (perhaps bottle fed babies go to the doctor less) than those of breast fed babies, and thus record fewer episodes of gastro-enteritis in them only.
This is called ias because the observation itself is in error.
EXAMPLE OF CONFOUNDING :
The mothers of breast-fed babies are of higher social class, and the babies thus have better hygiene, less crowding and perhaps other factors that protect against gastroenteritis. Crowding and hygiene are truly protective against gastroenteritis, but we mistakenly attribute their effects to breast feeding. This is called confounding. because the observation is correct, but its explanation is wrong.
PROTECTION AGAINST RANDOM ERROR AND RANDOM MISCLASSIFICATION:
Random error can work to falsely produce an association (type 1 error) or falsely not produce an association (type 2 error).
We protect ourselves against random misclassification producing a type 2 error by choosing the most precise and accurate measures of exposure and outcome.
PROTECTION AGAINST TYPE 1 ERRORS:
We protect our study against random type 1 errors by establishing that the result must be unlikely to have occurred by chance (e.g. p < .05). P-values are established entirely to protect against type 1 errors due to chance, and do not guarantee protection against type 1 errors due to bias or confounding. This is the reason we say statistics demonstrate association but not causation. PROTECTION AGAINST TYPE 2 ERRORS: We protect our study against random type 2 errors by providing adequate sample size, and hypothesizing large differences. The larger the sample size, the easier it will be to detect a true difference, and the largest differences will be the easiest to detect. (Imagine how hard it would be to detect a 1% increase in the risk of gastroenteritis with bottle-feeding). TWO WAYS TO INCREASE POWER: The sample size needed to detect a significant difference is called the power of a study. 1.Choosing the most precise and accurate measures of exposure and outcome has the effect of increasing the power of our study, because of variances of the outcome measures, which enter into statistical testing, are decreased. 2.Having an adequate sized sample of study subjects KEY PRINCIPLE IN BIAS AND CONFOUNDING :
The factor that creates the bias, or the confounding variable, must be associated with both the independent and dependent variables (i.e. with the exposure and the disease). Association of the bias or confounder with just one of the two variables is not enough to produce a spurious result.
In the example just given:
The BIAS, namely incomplete chart recording, has to be associated with feeding type (the independent variable) and also with recording of gastroenteritis (the dependent variable) to produce the false result.
The CONFOUNDING VARIABLE (or CONFOUNDER) better hygiene, has to be associated with feeding type and also with gastroenteritis to produce the spurious result.
Were the bias or the confounder associated with just the independent variable or just the dependent variable, they would not produce bias or confounding.
This gives a useful rule:
If you can show that a potential confounder is NOT associated with either one of the two variables under study (exposure or outcome), confounding can be ruled out.
SOME TYPES OF BIAS:
1. SELECTION BIAS
Any aspect of the way subjects are assembled in the study that creates a systematic difference between the compared populations that is not due to the association under study.
2. INFORMATION BIAS
Any aspect of the way information is collected in the study that creates a systematic difference between the compared populations that is not due to the association under study. (some call this measurement bias). The incomplete chart recording in the baby feeding example would be a form of information bias.
Other examples -
Diagnostic suspicion bias
Recall bias
Sometimes biases apply to a population of studies, rather than to one study, as in publication bias (tendency to publish papers which show positive results).
All analytic studies must begin with a clearly formulated hypothesis. The hypothesis must be quantitative and specific. It must predict a relationship of a specific size.
For example:
“Babies who are breast-fed have less illness than babies who are bottle-fed.”
Which illnesses? How is feeding type defined? How large a difference in risk?
A better example:
“Babies who are exclusively breast-fed for three months or more will have a reduction in the incidence of hospital admissions for gastroenteritis of at least 30% over the first year of life.”
Only specific prediction allows one to draw legitimate conclusions from a study which tests a hypothesis. But even with the best formulated hypothesis, two types of errors can occur.
• Type 1 - observing a difference when in truth there is none.
• Type 2 - failing to observe a difference when there is one.
These errors are generally produced by one or more of the following:
• RANDOM ERROR
• RANDOM MISCLASSIFICATION
• BIAS
• CONFOUNDING
RANDOM ERROR :
Deviation of results and inferences from the truth, occurring only as a result of the operation of chance. Can produce type 1 or type 2 errors.
RANDOM (OR NON-DIFFERENTIAL) MISCLASSIFICATION :
Random error applied to the measurement of an exposure or outcome. Errors in classification can only produce type 2 errors, except if applied to a confounder or to an exposure gradient.
BIAS:
Systematic, non-random deviation of results and inferences from the truth, or processes leading to such deviation. Any trend in the collection, analysis, interpretation, publication or review of data that can lead to conclusions which are systematically different from the truth.
Note that in bias, the focus is on an artifact of some part of the research process (assembling subjects, collecting data, analyzing data) that produces a spurious result. Bias can produce either a type 1 or a type 2 error, but we usually focus on type 1 errors due to bias.
Bias can be either conscious or unconscious. In epidemiology, the word bias does not imply, as in common usage, prejudice or deliberate deviation from the truth.
CONFOUNDING :
A problem resulting from the fact that one feature of study subjects has not been separated from a second feature, and has thus been confounded with it, producing a spurious result. The spuriousness arises from the effect of the first feature being mistakenly attributed to the second feature. Confounding can produce either a type 1 or a type 2 error, but we usually focus on type 1 errors.
THE DIFFERENCE BETWEEN BIAS AND CONFOUNDING:
Bias creates an association that is not true, but confounding describes an association that is true, but potentially misleading.
EXAMPLES OF RANDOM ERROR, BIAS, MISCLASSIFICATION AND CONFOUNDING IN THE SAME STUDY:
STUDY: In a cohort study, babies of women who bottle feed and women who breast feed are compared, and it is found that the incidence of gastroenteritis, as recorded in medical records, is lower in the babies who are breast-fed.
EXAMPLE OF RANDOM ERROR :
By chance, there are more episodes of gastroenteritis in the bottle-fed group in the study sample, producing a type 1 error. (When in truth breast feeding is not protective against gastroenteritis).
Or, also by chance, no difference in risk was found, producing a type 2 error (When in truth breast feeding is protective against gastroenteritis).
EXAMPLE OF RANDOM MISCLASSIFICATION :
Lack of good information on feeding history results in some breast-feeding mothers being randomly classified as bottle-feeding, and vice-versa. If this happens, the study finding underestimates the true RR, whichever feeding modality is associated with higher disease incidence, producing a type 2 error.
EXAMPLE OF BIAS:
The medical records of bottle-fed babies only are less complete (perhaps bottle fed babies go to the doctor less) than those of breast fed babies, and thus record fewer episodes of gastro-enteritis in them only.
This is called ias because the observation itself is in error.
EXAMPLE OF CONFOUNDING :
The mothers of breast-fed babies are of higher social class, and the babies thus have better hygiene, less crowding and perhaps other factors that protect against gastroenteritis. Crowding and hygiene are truly protective against gastroenteritis, but we mistakenly attribute their effects to breast feeding. This is called confounding. because the observation is correct, but its explanation is wrong.
PROTECTION AGAINST RANDOM ERROR AND RANDOM MISCLASSIFICATION:
Random error can work to falsely produce an association (type 1 error) or falsely not produce an association (type 2 error).
We protect ourselves against random misclassification producing a type 2 error by choosing the most precise and accurate measures of exposure and outcome.
PROTECTION AGAINST TYPE 1 ERRORS:
We protect our study against random type 1 errors by establishing that the result must be unlikely to have occurred by chance (e.g. p < .05). P-values are established entirely to protect against type 1 errors due to chance, and do not guarantee protection against type 1 errors due to bias or confounding. This is the reason we say statistics demonstrate association but not causation. PROTECTION AGAINST TYPE 2 ERRORS: We protect our study against random type 2 errors by providing adequate sample size, and hypothesizing large differences. The larger the sample size, the easier it will be to detect a true difference, and the largest differences will be the easiest to detect. (Imagine how hard it would be to detect a 1% increase in the risk of gastroenteritis with bottle-feeding). TWO WAYS TO INCREASE POWER: The sample size needed to detect a significant difference is called the power of a study. 1.Choosing the most precise and accurate measures of exposure and outcome has the effect of increasing the power of our study, because of variances of the outcome measures, which enter into statistical testing, are decreased. 2.Having an adequate sized sample of study subjects KEY PRINCIPLE IN BIAS AND CONFOUNDING :
The factor that creates the bias, or the confounding variable, must be associated with both the independent and dependent variables (i.e. with the exposure and the disease). Association of the bias or confounder with just one of the two variables is not enough to produce a spurious result.
In the example just given:
The BIAS, namely incomplete chart recording, has to be associated with feeding type (the independent variable) and also with recording of gastroenteritis (the dependent variable) to produce the false result.
The CONFOUNDING VARIABLE (or CONFOUNDER) better hygiene, has to be associated with feeding type and also with gastroenteritis to produce the spurious result.
Were the bias or the confounder associated with just the independent variable or just the dependent variable, they would not produce bias or confounding.
This gives a useful rule:
If you can show that a potential confounder is NOT associated with either one of the two variables under study (exposure or outcome), confounding can be ruled out.
SOME TYPES OF BIAS:
1. SELECTION BIAS
Any aspect of the way subjects are assembled in the study that creates a systematic difference between the compared populations that is not due to the association under study.
2. INFORMATION BIAS
Any aspect of the way information is collected in the study that creates a systematic difference between the compared populations that is not due to the association under study. (some call this measurement bias). The incomplete chart recording in the baby feeding example would be a form of information bias.
Other examples -
Diagnostic suspicion bias
Recall bias
Sometimes biases apply to a population of studies, rather than to one study, as in publication bias (tendency to publish papers which show positive results).
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