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A disease shows high prevalence yet low incidence. What best explains this?
ACases are being diagnosed at unusually early ages
BAffected people survive a long time without cure
CThe denominator was measured at mid-interval only
DNew cases arise faster than they can be recorded
Answer & Solution
Correct answer: B. Affected people survive a long time without cure
1. Prevalence is driven by two things: how many new cases arise, and how long each case lasts.
2. Incidence is stated to be low here, so new cases are not what is filling the prevalence pool.
3. That leaves long duration, meaning affected people survive a long time without being cured.
4. Age at diagnosis changes neither the number of cases nor how long they last.
5. The choice of denominator is a technical detail that affects both measures alike, and a high rate of new cases would contradict the low incidence given.
_Source: CDC Principles of Epidemiology in Public Health Practice (3rd ed., US federal, public domain), Lesson 3 "Measures of Risk", section Properties and uses of prevalence_
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