In public health, how do screening and prevention differ, and when is screening appropriate?

• A. Screening and prevention are the same; screening is always appropriate.
• B. Screening identifies disease in asymptomatic individuals; prevention aims to reduce incidence or progression; screening is appropriate when disease burden is high, test is valid, and early treatment improves outcomes.
• C. Prevention identifies disease in asymptomatic individuals; screening reduces incidence.
• D. Screening only occurs after symptoms appear.

Answer: (B)

Screening is a secondary prevention activity that looks for disease in people who have no symptoms, while prevention includes actions to stop disease from occurring (primary prevention) or to prevent its progression (secondary prevention in some contexts). The best answer captures this distinction and adds when screening should be used: screening is appropriate when the disease burden in the population is high enough to justify testing, the screening test is valid (accurate and reliable), and there is evidence that detecting the disease early and treating it will improve outcomes.

This is why screening isn’t always appropriate—if the disease is rare, the test isn’t accurate, or early detection doesn’t improve outcomes, screening can do more harm than good. For example, a screening test with many false positives can lead to unnecessary anxiety and procedures, while a poor-targeted screen wastes resources.