Disaster epidemiology


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Disaster epidemiology

  1. 1. Epidemiology of disasters David Alexander University College London
  2. 2. Botulism Cholera Diphteria Salmonella Typhoid
  3. 3. The risk of increased transmission of disease after a disaster comes from:• the disaster itself (e.g. fecal contamination of potable water) • disruption of normal programmes of disease control and prevention • overcrowding and bad hygiene in survivors' camps.
  4. 4. Theoretical risk of communicable disease Disaster Cold wave Person to person In water In food By vector Low Low Low Low Medium Medium Medium Low Famine High Medium Medium Medium Fire Low Low Low Low Medium High Medium High Heat wave Low Low Low Low Hurricane Medium High Medium High Low Low Low Low Medium Medium Medium Low Earthquake Flood Tornado Volcanic eruption
  5. 5. The main risks come from endemic diseases.
  6. 6. Bad response to disease risks:- • mass vaccination of survivors • indiscriminate burial or cremation • sanitary cordons around the affected area • indiscriminate mass disinfection or disinfestation.
  7. 7. Wenchuan, Sichuan, China, May 2008
  8. 8. Good responses to the problem: • epidemiological surveillance (but this will increase the diagnosis rate) • routine prophyllaxis of health workers.
  9. 9. The values of mortality and morbidity (i.e. dead and injured or infected) are expressed as: ( numerator / denominator ) This means the frequency of a measured or observed state or event, divided by the total number of people who are exposed to that state or event (the population at risk).
  10. 10. A static measure – prevalence rate: the proportion of a given group of people who have a given condition at a single moment in time. Period prevalence rate: when a particular period of time is needed to count or register all the people who have the given condition.
  11. 11. A dynamic measure – incidence rate: the proportion of a group of people who develop a given condition over a specified time period. Non-standardised incidence rate: without reference to population size.
  12. 12. Standardised incidence rate: raw value corrected by • size of the population • (e.g., number of deaths per 10,000 people) • age-group (e.g. 0-4 = infants, 4-15 = children, 16+ = adults). The population is defined as all the people who could possibly catch the disease or have the condition in question.
  13. 13. Outbreak: various cases Epidemic: many cases Pandemic: a large, international epidemic • there are no quantitative definitions of these terms.
  14. 14. Epidemiological surveillance should make use of:• existing standardised statistical protocols • unofficial information from the community (it needs to be verified) • reports from field workers and their organisations.
  15. 15. In normal times, surveillance concentrates on diseases that are:- • locally endemic • capable of being controlled • of public health importance • monitored under WHO disease control programmes.
  16. 16. New, post-disaster surveillance should be more focussed on symptoms and conditions that are:• directly attributable to the disaster • capable of being controlled.
  17. 17. The aim of epidemiological surveillance is:• to collect data on the risks and incidence of particular diseases and medical conditions • to prevent epidemics and restrict the progress of given pathologies.
  18. 18. The specific objectives of epidemiological surveillance • technical: timely identification to facilitate rapid response • social: stop rumours, give the public a sense of security • operative: avoid inefficient measures of disease prevention.
  19. 19. The surveillance should monitor:• diseases that occur during normal times • diseases that may be transmitted as a result of the disaster • rarer diseases that are monitored under WHO protocols.
  20. 20. Methods of post-disaster surveillance • open an epidemiological observatory in the disaster area • receive information and data every day by phone, fax, email, sitrep, etc. • create a system of rapid investigation of any apparent anomalies in disease transmission.
  21. 21. Data to be recorded • bacteriologically confirmed cases of disease • suspected clinical syndrome (i.e. symptoms): - diarrhoea, cough, dermatitis, etc. - diarrhoea with blood, mucus, etc. - fever with diarrhoea, etc.
  22. 22. Disease Baccillary dysentery Blenorrhoea Botulism Brucellosis Cholera Dengue Diphteria Infectious parotitis Leptospirosis Meningococcal meningitis Incubation period (days) 1-7 5-12 0.5-1.5 5-21 0.5-5 8-11 2-5 12-26 4-19 2-10 Period of communicability ≤28 days 10 months --about 7 days -≤28 days ≤9 days -rapid
  23. 23. Disease Period of communicability Poliomielitis Incubation period (days) 3-21 Scarlattina Tetanus Tuberculosis 1-3 4-21 28-84 10-21 days -some weeks Typhoid Varicella Hepatitis A 7-21 14-21 15-50 variable ≤27 days 30-50 days Hepatitis B 45-160 100-160 days 7-21 ≤21 days Pertosse ≤42 days
  24. 24. Cases of typhoid identified two days after a flood (a) are an effect of the flood. (b) are not an effect of the flood. Natural disasters (a) often end with large epidemics of communicable disease. (b) rarely end with large epidemics of communicable disease.
  25. 25. When various cases of a communicable disease are reported in an area that has recently been affected by a disaster: (a) the disease has probably been brought into the area by rescuers. (b) the disease is probably endemic to the area.
  26. 26. The incidence of certain communicable diseases is internationally notifiable: (a) because people who go into the disaster area may be disease carriers. (b) because these diseases are part of international monitoring and control programmes.
  27. 27. After a disaster, mass vaccination: (a) is the only acceptabe response to the increased risk of communicable disease transmission. (b) is a waste of time, money and vaccine. 'Morbidity' refers to: (a) the rate of injury or disease. (b) the tendency of survivors to be clinically depressed, in some cases as a result of injuries received.
  28. 28. Disaster epidemiologists (a) use mass prophyllaxis to try to stop the progress of communicable diseases. (b) try to stop the progress of communicable diseases by investigating the social and environmental conditions that give rise to those diseases.
  29. 29. Epidemiological monitoring after disasters should include: (a) probable clinical syndromes, but not apparent symptoms. (b) probable clinical syndromes and apparent symptoms. After a disaster: (a) children should be vaccinated against selected diseases. (b) children absolutely should not be vaccinated against any diseases.
  30. 30. When vaccines against typhoid and cholera are properly used (a) are perfectly effective. (b) are not perfectly effective. The incidence rate of a disease is (a) a static measure, while the prevalence is a dynamic measure of the progress of the disease. (b) a dynamic measure, while the prevalence rate is a static measure of the progress of the disease.
  31. 31. Disaster epidemiologists: (a) investigate rumours about the progress of diseases. (b) usually ignore rumours about the progress of diseases. In an area affected by a disaster, the rate of diagnosis of diseases and conditions (a) will probably go up during the emergency phase. (b) will probably go down during the emergency phase. [X]