Download Study Session 42 Epidemic Investigation and Management

42. Epidemic Investigation and
Management
Study Session 42 Epidemic Investigation and Management ...................................... 3
Introduction .............................................................................................................. 3
Learning Outcomes for Study Session 42 ................................................................ 3
42.1 What is an outbreak and an epidemic? ........................................................... 3
Question ............................................................................................................... 3
Answer ................................................................................................................. 4
42.2 Types of epidemics ......................................................................................... 4
Question ............................................................................................................... 4
Answer ................................................................................................................. 4
42.2.1 Common source outbreaks ....................................................................... 4
Question ............................................................................................................... 5
Answer ................................................................................................................. 6
42.2.2 Propagated or progressive epidemics....................................................... 7
Question ............................................................................................................... 7
Answer ................................................................................................................. 7
42.2.3 Mixed epidemics ...................................................................................... 7
Question ............................................................................................................... 7
Answer ................................................................................................................. 7
42.3 Epidemic investigation.................................................................................... 8
Box 42.1 Steps in an epidemic investigation ...................................................... 9
42.4 Management of epidemics .............................................................................. 9
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Summary of Study Session 42 ............................................................................... 11
Self-Assessment Questions (SAQs) for Study Session 42 .................................... 11
SAQ 42.1 (tests Learning Outcomes 42.1 and 42.2) ......................................... 11
Answer ............................................................................................................... 11
SAQ 42.2 (tests Learning Outcome 42.4) .......................................................... 12
Answer ............................................................................................................... 12
SAQ 42.3 (tests Learning Outcomes 42.1 and 42.2) ......................................... 12
Answer ............................................................................................................... 12
SAQS 42.4 (tests Learning Outcomes 42.1, 42.3 and 42.4) .............................. 12
Answer ............................................................................................................... 13
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Study Session 42 Epidemic
Investigation and Management
Introduction
In Study Sessions 40 and 41 you learned that one use of surveillance is to find out
if there is an unusual increase in cases of any communicable diseases in your
community, which could signal the start of an outbreak or epidemic. In this final
study session, you will learn more about the different kinds of epidemics and how
to investigate and manage them. A better understanding of epidemics will help you
to detect an outbreak or epidemic of a communicable disease and report it
immediately to the Health Centre and/or District Health Office. You are also
expected to help the District Health Team in the control of any epidemics in your
catchment area.
Learning Outcomes for Study Session 42
When you have studied this session, you should be able to:
42.1 Define and use correctly all of the key words printed in bold.
(SAQs 42.1, 42.3 and 42.4)
42.2 Describe the different types of epidemics. (SAQs 42.1 and 42.3)
42.3 Describe the purpose of epidemic investigation. (SAQ 42.4)
42.4 Explain in outline the basic principles of epidemic management. (SAQs 42.2
and 42.4)
42.1 What is an outbreak and an epidemic?
If there is an increase in cases of a disease compared with the expected number, but
it lasts for only a short time, or it occurs only in a limited area (e.g. in a few nearby
households), the rise may be referred to as an outbreak. As you will remember
from Study Session 1 of this Module, an epidemic is also an excess of cases
compared with the number expected. However, an epidemic is more general than an
outbreak, the increase in the number of cases continues far longer (possibly months
or even years), and the cases are distributed across a wider area.
For example, it may be that during January to March there are normally fewer than
10 cases of tuberculosis (TB) in your kebele. If you found 30 cases of tuberculosis
in a particular January, followed by 39 cases in February and 45 cases in March,
then you would strongly suspect that there was an epidemic of TB in your
community. You would then need to find out why TB had suddenly increased.
Question
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Which disease often causes epidemics during the months of June, September and
October in Ethiopia? Why are these the months when these epidemics most often
occur?
Answer
Malaria is the major vector-borne disease that causes epidemics in the months of
June, September and October in Ethiopia. This is when the conditions are humid
and warm enough and there are plentiful water collections for the vector
mosquitoes to breed in. You learned about malaria in Study Sessions 5–12 of this
Module.
End of answer
42.2 Types of epidemics
Epidemics are classified into different types according to the source of infection
and modes of transmission.
Question
From Study Session 1 of this Module, briefly describe the two main modes of
transmission of communicable diseases.
Answer
They are: (1) direct modes of transmission, such as from mother to child, or from
faecally contaminated hands into the mouth; and (2) indirect modes of
transmission, such as through vectors, contaminated air, water, food or objects such
as cooking bowls and utensils.
End of answer
Based on criteria such as this, epidemics are classified into three types:



common source outbreaks
propagated or progressive epidemics
mixed epidemics.
We will look at each of them in turn.
42.2.1 Common source outbreaks
Common source outbreaks occur when the rise in cases of an infection occurs
after a group of people all came into contact with the same unsafe source of
infection (the common source), such as contaminated food or water. For example,
imagine a wedding where food was prepared in the morning to serve to wedding
guests in the evening. If the prepared food was left outside on a hot day under the
sun until evening, bacteria might multiply in the food. If this food was served to the
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guests in the evening without reheating it thoroughly, many of the guests might fall
ill from eating the contaminated food (Figure 42.1). This kind of epidemic is called
a common source outbreak because the affected guests all ate the same
contaminated food at the wedding.
Figure 42.1 Guests eating contaminated food during the wedding become ill with
diarrhoea and vomiting; the most severely affected are too ill to get up.
Question
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After the food had been prepared in the morning, explain what should have been
done to make it safe to serve to the wedding guests in the evening.
Answer
Bacteria like moisture and warmth, and they multiply quickly in food left in hot sun
for many hours. After the food had been prepared, it should have been kept covered
in a refrigerator (Figure 42.2) or in a cool place inside the house, away from direct
sun. The food should also have been reheated thoroughly before being served to the
guests.
Figure 42.2 Refrigerating food reduces the risk of a common source outbreak of a
foodborne infection.
End of answer
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A point source outbreak is a common source outbreak where the exposure period
(e.g. the time at which the contaminated food was eaten) is short. This means that
all cases who fall ill after eating the food (the common source) also have the same
incubation period, i.e. the period between infection (eating the contaminated food)
and the appearance of the first symptoms.
42.2.2 Propagated or progressive epidemics
Propagated or progressive epidemics occur when the infection spreads from
person to person. The infectious agents causing the disease pass from one host to
another, either directly from person to person (e.g. via hand shaking or kissing), or
indirectly via vectors (e.g. mosquitoes in the case of malaria), or in water, food or
another medium. The distribution of malaria cases is a good example of a
propagated epidemic, because increased numbers of malaria cases occur again and
again at different times. Propagated epidemics last longer than the common source
outbreaks described above. This is because malaria will continue to spread in the
community, as long as mosquitoes are present in the environment and there are
people who carry the parasite.
Question
Can you think of any epidemic-prone diseases that spread quickly in overcrowded
conditions where there is poor sanitation and personal hygiene?
Answer
You may have thought of typhoid fever, cholera, shigellosis (bacterial dysentery),
louse-borne relapsing fever and typhus. (Think back to Study Sessions 33 and 36.)
End of answer
42.2.3 Mixed epidemics
Mixed epidemics show characteristics of both common source and propagated
epidemics. So a mixed epidemic can start with a common source and be followed
by a propagated spread. Mixed epidemics are often caused by foodborne infectious
agents.
Question
Typhoid fever can easily spread and become a propagated epidemic. Can you
remember from Study Session 33 how the typhoid bacteria are transmitted from
person to person?
Answer
Typhoid bacteria are transmitted from infected people to new susceptible hosts via
contaminated food or water.
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End of answer
The organism that causes typhoid (Salmonella typhi) can survive in sewage for 14
days and in water for up to seven days. Water polluted by faecal matter is therefore
the main source of infection for typhoid. If the whole community drinks water from
the same water source (Figure 42.3), which has been contaminated with Salmonella
typhi, there will be a common source outbreak of typhoid fever. The epidemic may
continue to spread through faecal matter passing from person to person, if the
people in the affected community do not improve their standards of personal
hygiene, or if the water is not treated and made safe to drink. This type of spread of
typhoid is called a propagated epidemic of typhoid.
Figure 42.3 Drinking water collected from the same unsafe source can expose a
whole community to waterborne infection and lead to a common source outbreak,
followed by a propagated spread. (Photo: Basiro Davey)
42.3 Epidemic investigation
Epidemic investigation is a set of procedures used to identify the cause, i.e. the
infectious agent, responsible for the disease. It is also used to identify the people
affected, the circumstances and mode of spread of the disease, and other relevant
factors involved in propagating the epidemic. This is especially important if the
epidemic has unusual features, if it presents a significant threat to public health, and
it is not self-limiting (i.e. it does not end spontaneously without professional
intervention).
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Epidemic investigation is a challenging task for health workers. The main purpose
of epidemic investigation is to control the spread of the disease before it causes
more deaths and illness. As a Health Extension Practitioner, the first action you
should take is to confirm the existence of an epidemic. To do this, you need to
know the average number of cases of that disease during this specific month in your
community in previous years, so you can compare that number with the current
number of cases. Is there an excess number of cases or deaths from this disease
compared to the usual occurrence? If there really are excess cases, you should
report your findings to the District Health Office immediately. The reporting
formats were given in Study Session 41.
The next steps (Box 42.1) will be taken by the District Epidemic Management
Team, which is composed of many different health professionals such as doctors,
nurses, environmental experts and others. These steps include confirming the cause
(the infectious agent involved), the number of people affected (the cases) and the
modes of transmission of the infection from cases to new susceptible hosts.
Box 42.1 Steps in an epidemic investigation
1. Establish the existence of an outbreak
2. Verify the diagnosis or causes
3. Define and identify cases:
1. Use a standard case definition (see Study Session 41)
2. Identify and count cases
4. Perform descriptive epidemiology, i.e. collect data on the age, sex, etc. of the
cases and analyse the data to see if useful patterns emerge
5. Develop hypotheses to explain the occurrence of the epidemic:
1. Evaluate the hypotheses
2. Reconsider/refine the hypotheses
6. Carry out additional studies to confirm or reject the explanations for the
epidemic:
1. Additional epidemiological studies
2. Other types of studies, e.g. laboratory tests, environmental
investigations
7. Implement control and prevention measures
8. Communicate findings to higher levels in the health system, community
leaders and other local stakeholders.
42.4 Management of epidemics
Epidemic management activities include taking appropriate control measures, such
as treating those who are ill to reduce the reservoir of infection, and providing
health education to limit the transmission of the disease to others. Health
professionals at higher levels will require your help in putting into taking any
measures needed to control the spread of the disease, such as giving drugs to people
in the community and providing health education.
As mentioned above, you may be involved in the management of an epidemic once
it is confirmed by the health authorities. The type of control measures you need to
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implement depend on the type of infectious agent, how the disease is transmitted,
and any other factors contributing to the disease. Generally, your control measures
should target the infectious agent, the source of any infection, and the treatment of
those who became ill. Remember, the source of infection could be humans or
animals, or non-living things in the environment.
If you do not implement the correct control measures, the epidemic may continue to
spread in your area. For example, if contaminated food is the source of an outbreak
in your community, you will need to control the outbreak by teaching the
community about food hygiene (Figure 42.4), so they are not exposed to
contaminated food. If it is caused by contaminated water, you should educate them
not to drink the water until it is treated with chlorine. If mosquito breeding sites are
the source of a malaria epidemic, you will need to teach the community to clear the
breeding sites for mosquitoes.
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Figure 42.4 Teaching community members about preparing food safely can
prevent an epidemic of foodborne infection.
This short discussion of epidemic investigation and management brings the
Communicable Diseases Module to a close. We hope that after studying the 42
study sessions and completing your practical training attachments, you will feel
confident to identify, treat, refer, prevent and control communicable diseases
effectively in your community, and report cases accurately and at the proper time.
Summary of Study Session 42
In Study Session 42, you have learned that:
1. An epidemic is the occurrence of more cases of a disease than would be
expected in the population at that period of time. An outbreak is an increase
in cases for a short time in a limited area.
2. A common source outbreak is an epidemic which arises from a single source
of infection, and where most people fall ill after the same incubation period.
3. A propagated epidemic occurs when the infection spreads from one person to
another, e.g. through the air, via a vector, via contaminated food or water, or
during unprotected sexual intercourse.
4. A mixed epidemic can start with a common source and be followed by a
propagated spread.
5. An epidemic investigation is conducted to rapidly identify the cause of an
outbreak or epidemic and to take effective actions to contain and prevent the
spread of the disease.
6. Epidemic investigation and management involves team work. Your role as a
Health Extension Practitioner is to report the occurrence of an epidemic, to
mobilise and educate the community, and to assist the District Health
authorities in carrying out control and prevention measures as required.
Self-Assessment Questions (SAQs) for Study Session
42
Now that you have completed this study session, you can assess how well you have
achieved its Learning Outcomes by answering these questions. Write your answers
in your Study Diary and discuss them with your Tutor at the next Study Support
Meeting. You can check your answers with the Notes on the Self-Assessment
Questions at the end of this Module.
SAQ 42.1 (tests Learning Outcomes 42.1 and 42.2)
Explain the difference between common source and propagated epidemics, and
give one example of each.
Answer
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In a common source epidemic, there is a single source of infection and most people
develop the disease after the same incubation period. Good examples are foodborne
diarrhoeal diseases. In propagated epidemics, the disease is transmitted from person
to person via, for example, a vector, respiratory droplets coughed or sneezed into
the air, sexual contact, or some other direct or indirect method. Good examples are
a malaria epidemic, or louse-borne relapsing fever or typhus.
End of answer
SAQ 42.2 (tests Learning Outcome 42.4)
If an outbreak is spread via a contaminated community water supply in your
catchment area, what action should you take as a Health Extension Practitioner?
Answer
Educate the community to boil the water or add chemicals such as chlorine before
drinking the water.
End of answer
SAQ 42.3 (tests Learning Outcomes 42.1 and 42.2)
What differences would you expect to find if you could measure a. the incubation
period in an epidemic of HIV/AIDS in a village and b. the incubation period in an
epidemic caused by eating contaminated food at a birthday celebration?
Answer
1. HIV/AIDS occurs in propagated epidemics. Therefore, in an HIV/AIDS
epidemic, the people affected will not become sick after the same incubation
period, because they were infected at different times and from different
sources.
2. By contrast, in a common source outbreak of a foodborne infection, most
people will become sick after the same, single incubation period because they
acquired the infection from the same food at the birthday celebration.
End of answer
SAQS 42.4 (tests Learning Outcomes 42.1, 42.3 and 42.4)
Suppose at your Health Post you have seen 11 cases in three days of people who
have acute watery diarrhoea, and recorded them as in Table 42.1. One patient (case
7) died soon after arrival at the Health Post.
1. Describe the distribution of the cases by the sex of the patients.
2. What diagnosis do you suspect from reviewing these 11 cases? Explain your
answer.
3. What action should you take?
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Table 42.1 Number of cases of acute watery diarrhoea recorded at a Health
Post during a period of three days in 2002 (Ethiopian calendar).
Case Age in years Occupation Sex Address/kebele Date illness began
1
25
Teacher
Male 01
Jan 3, 2002
2
29
Housewife Female 01
Jan 4, 2002
3
45
Farmer
Male 01
Jan 5, 2002
4
35
Farmer
Male 01
Jan 4, 2002
5
38
Teacher
Female 01
Jan 5, 2002
6
25
Day worker Female 01
Jan 4, 2002
7
10
Child
Male 01
Jan 4, 2002
8
29
Housewife Female 01
Jan 4, 2002
9
22
Housewife Female 01
Jan 3, 2002
10 39
Farmer
Male 01
Jan 3, 2002
11 21
Farmer
Male 01
Jan 5, 2002
Answer
1. There are 6 males and 5 females with acute watery diarrhoea.
2. The number of cases (11) is high in three days and may indicate the
occurrence of a cholera epidemic. In particular, the death of a person over 5
years old from diarrhoea is an indicator of cholera (think back to Study
Session 33).
3. Immediately report these cases and your suspected diagnosis of cholera to the
District Health Office for further investigation and management. Go into the
community and see if you can find other similar cases. Educate community
members on how they can prevent the spread of the infection.
End of answer
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