The risk of communicable disease transmission increases after disasters due to contamination of water supplies, disruption of disease prevention programs, and overcrowding in shelters. Diseases like cholera, typhoid, and hepatitis spread easily in these conditions. Surveillance is important to identify outbreaks early and target control measures. Key responses include epidemiological monitoring of endemic and disaster-related illnesses, investigation of anomalies, and routine preventative treatment of health workers. Mass vaccination or treatment should be avoided without cause. The goal is to curb epidemics through timely response based on surveillance data.

1. Epidemiology
of disasters
David Alexander
University College London

2. Botulism
Cholera
Diphteria
Salmonella
Typhoid

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. 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. The main risks come
from endemic diseases.

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. Wenchuan, Sichuan, China, May 2008

8. Good responses to the problem:
• epidemiological surveillance
(but this will increase
the diagnosis rate)
• routine prophyllaxis
of health workers.

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. 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. 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. 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. Outbreak: various cases
Epidemic: many cases
Pandemic: a large, international
epidemic
• there are no quantitative
definitions of these terms.

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. 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. New, post-disaster surveillance
should be more focussed on
symptoms and conditions that are:• directly attributable to the disaster
• capable of being controlled.

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.
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