Which statement correctly distinguishes attack rate and case fatality rate?

• A. Attack rate measures deaths among identified cases; case fatality rate measures new cases during an outbreak.
• B. Attack rate measures the frequency of new cases during an outbreak; case fatality rate is the proportion of deaths among identified cases.
• C. Attack rate measures chronic disease prevalence; case fatality rate measures test accuracy
• D. Attack rate measures prevalence of disease; case fatality rate measures duration of illness

Answer: (B)

The key distinction is that attack rate measures the risk of getting the disease in a defined population over a short time during an outbreak, while case fatality rate measures how deadly the disease is among those who have it. Attack rate counts new cases in a population at risk and divides by the at-risk population, often expressed as a percentage or per 1,000 or 100,000 people. Case fatality rate, on the other hand, is the proportion of deaths among identified cases, calculated as deaths divided by the number of identified cases. This reflects severity among those with the disease and depends on how thoroughly cases are detected and how long follow-up lasts. So the statement that attack rate measures the frequency of new cases during an outbreak and case fatality rate is the proportion of deaths among identified cases is the correct distinction.