For a highly fatal disease with short duration, which statement is true?

• A. Mortality rates will be much higher than incidence rates
• B. Incidence rates will be much higher than mortality rates
• C. Incidence rates will be unrelated to mortality rates
• D. Incidence rates and mortality rates will be similar

Answer: (D)

When a disease is highly fatal and of short duration, people who become cases move rapidly through the disease course and either die or recover in a very brief time. Because the time window from a new case to its outcome is short, the number of new cases in a given period tends to be similar to the number of deaths from the disease in that same period. In other words, incidence (new cases) and mortality (deaths) run in tandem under these conditions, so their rates in a population are roughly similar. Prevalence remains low because people don’t stay ill for long.

That’s why the statement that incidence rates and mortality rates will be similar is the best choice. The other options imply a mismatch or unrelatedness between the two rates, which doesn’t fit a disease that causes rapid progression to death.