What is the measure describing the frequency and speed of spread of disease in a population at risk?

• A. Attack rate
• B. Prevalence
• C. Incidence rate
• D. Mortality rate

Answer: (A)

The measure describes how often a disease appears and how quickly it spreads through a group that is at risk during a defined time. This is captured by the attack rate, which looks at the number of new cases among people who could get the disease (the at-risk population) over a specific period and expresses it as a proportion or percentage. It’s especially useful in outbreak investigations because it directly shows, in a short window, how many people became ill among those exposed or present.

Prevalence tells you how many people have the disease at a given moment, including existing cases, but it doesn’t reflect new cases or how fast the illness is spreading. Incidence rate (incidence density) measures new cases per person-time and focuses on the risk over time with precise time-at-risk data, which is more about the flow of new cases over time rather than the rapid spread in a defined outbreak. Mortality rate, on the other hand, concerns deaths due to the disease in a population, not the frequency of disease occurrence or its spread.