SPEX Preventive Medicine 4

Question 1

A new diagnostic test for diabetes has a sensitivity of 90% and specificity of 85%. In a population with 10% prevalence, what is the positive predictive value (PPV)?

Accepted Answer

Approximately 40%

Answer

Using Bayes' theorem: PPV = (0.90×0.10)/[(0.90×0.10)+(0.15×0.90)] = 0.09/0.225 ≈ 40%.

Question 2

Which occupational lung disease is caused by inhalation of free crystalline silica and is associated with increased risk of tuberculosis?

Accepted Answer

Silicosis

Answer

Silicosis from silica dust exposure impairs pulmonary macrophage function, substantially increasing susceptibility to tuberculosis.

Question 3

The 'healthy worker effect' in occupational epidemiology refers to:

Accepted Answer

Employed populations appear healthier than the general population because severely ill individuals are less likely to work

Answer

The healthy worker effect biases occupational studies toward lower observed mortality because the employed tend to be healthier than the general population.

Question 4

Which clinical preventive service is recommended by the USPSTF with a Grade B recommendation for all adults aged 35–70 who are overweight or obese?

Accepted Answer

Screening for prediabetes and type 2 diabetes

Answer

USPSTF gives a Grade B recommendation for prediabetes/type 2 diabetes screening in overweight or obese adults aged 35–70.

Question 5

In communicable disease control, 'herd immunity threshold' is calculated as 1 − (1/R₀). For measles with an R₀ of 15, what percentage of the population must be immune?

Accepted Answer

93%

Answer

1 − (1/15) = 1 − 0.067 ≈ 0.933, meaning approximately 93% of the population must be immune.

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SPEX Exam Practice Test

SPEX Preventive Medicine 4