DHA Public Health & Epidemiology

Question 1

In a city of 200,000 people, 400 new cases of tuberculosis are diagnosed during one year. The total number of active TB cases at year-end is 1,200. What is the annual INCIDENCE rate per 100,000 population?

Accepted Answer

200 per 100,000

Answer

Incidence = new cases / population at risk × 100,000 = 400 / 200,000 × 100,000 = 200 per 100,000. Prevalence would use total active cases (1,200), giving 600 per 100,000.

Question 2

A screening test for hepatitis C has a sensitivity of 95% and a specificity of 90%. In a population where the true prevalence is 1%, which statement is CORRECT?

Accepted Answer

The positive predictive value will be low despite high sensitivity

Answer

When prevalence is low (1%), even a highly sensitive test produces many false positives relative to true positives, resulting in a low positive predictive value (PPV). PPV depends heavily on disease prevalence, not just test characteristics.

Question 3

A national program provides vitamin A supplements to all children under 5 to prevent blindness. This is an example of which level of prevention?

Accepted Answer

Primary prevention

Answer

Primary prevention aims to prevent disease before it occurs. Supplementing healthy children to prevent vitamin A deficiency and its complications (blindness) acts before any disease develops. Secondary prevention involves screening for early disease; tertiary prevents disability from established disease.

Question 4

A cohort study follows 500 smokers and 500 non-smokers for 10 years. Among smokers, 50 develop lung cancer; among non-smokers, 5 develop lung cancer. What is the relative risk (RR) of lung cancer in smokers?

Accepted Answer

10

Answer

RR = (risk in exposed) / (risk in unexposed) = (50/500) / (5/500) = 0.10 / 0.01 = 10. Smokers are 10 times more likely to develop lung cancer than non-smokers in this study.

Question 5

According to WHO and Dubai Health Authority communicable disease protocols, a healthcare provider who diagnoses a case of cholera must report it to public health authorities within:

Accepted Answer

Immediately (within 24 hours)

Answer

Cholera is a Category 1 notifiable disease under international health regulations (IHR 2005), requiring immediate notification (within 24 hours) to allow rapid outbreak response. Delayed reporting significantly hampers containment.

DHA - Dubai Health Authority Practice Test

DHA - Dubai Health Authority Practice Test

DHA Public Health & Epidemiology