Calculate attack rates, food- or source-specific attack rates with the attack rate ratio, and secondary attack rates during an outbreak investigation.
About this tool
Attack rates, secondary attack rate and exposure comparison for outbreaks.
How to use Attack Rate Calculator
- Choose overall attack rate, exposed versus unexposed, or secondary attack rate.
- Enter the ill and total counts for each group.
- Read the attack rates, their ratio and confidence intervals.
Worked example
38 of 60 people who ate the chicken salad fell ill against 4 of 90 who did not: an attack rate ratio of 14.25.
What is an attack rate?
The proportion of an exposed population who become ill during an outbreak. It is a cumulative incidence over a short period.
What is a secondary attack rate?
The share of susceptible contacts of a case who become ill, which measures person-to-person spread.
Explore Medical & Clinical Tools · More practical guides