The statement, 'The attack rate is the proportion of at-risk individuals who develop disease during a defined period,' is:

• A. True
• B. False
• C. Only for chronic diseases
• D. It is the same as prevalence

Answer: (A)

Attack rate is a measure of risk during an outbreak, representing the proportion of people at risk who develop the disease over a defined period. It is calculated as the number of new cases during the outbreak divided by the number of people at risk at the start of observation, often expressed as a percentage. This aligns with the statement that the attack rate is the proportion of at-risk individuals who develop disease during a defined period, so the statement is true. It is particularly used for acute outbreaks where the population at risk and the exposure period are clearly defined, not for chronic diseases which unfold over longer times. It differs from prevalence, which counts all existing cases (both new and old) at a point or over a period rather than focusing only on new cases in a defined time window.