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.


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.

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?


Educate the community to boil the water or add chemicals such as chlorine before drinking the water.

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?


  • a.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.
  • b.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.

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.

  • a.Describe the distribution of the cases by the sex of the patients.
  • b.What diagnosis do you suspect from reviewing these 11 cases? Explain your answer.
  • c.What action should you take?

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).

CaseAge in yearsOccupationSexAddress/kebeleDate illness began
125TeacherMale01Jan 3, 2002
229HousewifeFemale01Jan 4, 2002
345FarmerMale01Jan 5, 2002
435FarmerMale01Jan 4, 2002
538TeacherFemale01Jan 5, 2002
625Day workerFemale01Jan 4, 2002
710Child Male01Jan 4, 2002
829HousewifeFemale01Jan 4, 2002
922HousewifeFemale01Jan 3, 2002
1039FarmerMale01Jan 3, 2002
1121FarmerMale01Jan 5, 2002


  • a.There are 6 males and 5 females with acute watery diarrhoea.
  • b.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).
  • c.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.

Summary of Study Session 42