Please read the following case and answer the associated questions. The followin

Question

Please read the following case and answer the associated questions.

The following case study was adapted from the CDC Epidemiology Program Office, Case Studies in Applied Epidemiology, No. 891-903.

It is the early 1990s. The World Health Organization is planning a program for the global eradication of polio by the year 2000. Likura, a fictitious nation south-central Africa, may become one of the countries selected to test the effectiveness of WHOs polio eradication strategies. Unfortunately, little is known about polio in Likura. The Minister of Health therefore assigned the task of assessing the polio situation to a Ministry worker who has recently returned from an epidemiology course in Atlanta, and who is about to become the District Health Officer in the Ababo District. The Ababo District is a relatively poor rural district with a single hospital and several health centers. The Ababo District has attempted to conduct surveillance on polio cases and deaths over the past five years. The hospital, health centers, and all health workers are supposed to report such cases to the District Health Officer.

One measure of the polio situation in a community is the prevalence of lameness in children, since lameness is a common sequel of polio.

Question 1a: What data might you use (or collect) to determine the incidence of polio in the population?

Question 1b: What data might you use (or collect) to determine the prevalence of polio in the population?

Question 2: What is the difference between active and passive surveillance systems? Is the Ababo surveillance system for polio passive or active?

To gather information on polio prevalence, vaccine coverage, and risk factors for polio, the District Health Officer conducted a survey of children in the district. Lameness was used as a surrogate for polio. The prevalence of lameness by vaccination status is shown in Table 4.

Table Lameness by Vaccination Status among Children 12-23 Months of Age, Ababo District, 1991.

Lame

Normal

Polio Vaccine

1 dose

1

242

243

0 doses

9

667

676

10

909

919

Question 3: What is the prevalence of polio (lameness) among vaccinated (1 dose) children?

Question 4: What is the prevalence of polio (lameness) among the unvaccinated children?

Question 5: What is the vaccine coverage (at least one dose) in this population?

Question 6: Interpret these data.

Lame

Normal

Polio Vaccine

1 dose

1

242

243

0 doses

9

667

676

10

909

919

Explanation / Answer

1.a. The data can be collected from hospitals and healthcare centers to get the number of incidence of polio. The cases having symptoms indicating polio should be recorded such as flaccid paralysis.

1.b. The record showing the presence of lameness is to be collected.

2. Active surveillance means continuous survey and collection of reports on regular basis by healthcare authorities. Whereas, passive surveillance rely on the reports obtained from healthcare department based on certain rules.

In case of Ababo district, the cases of polio are reported to the district health officer by hospitals, health workers etc. so this is a passive surveillance system in Ababo.

3. Prevalence of polio among vaccinated children can be calculated as:

Prevalence = (number of polio cases/ total population) X 100

     = (1/243) X 100

    = 0.41 %

4. Prevalence of polio among unvaccinated children will be:

Prevalence = (9/676) X 100

     = 1.33 %

5. Vaccine coverage = (vaccinated population/ total population) X 100

             = (243/ 919) X 100

             = 26.44 %

6. Data interpretation:

In a data having vaccine coverage of 26.44% of total population, the prevalence of polio is found to be less i.e. 0.41 % of population of 243 vaccinated children, compared to prevalence of polio in case of unvaccinated population of 676 children where prevalence is found to be higher i.e. 1.33 %. Prevalence of polio is found to be decreased with vaccination.

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