The attack rate is a measure used in epidemiology to describe the proportion of a population that becomes ill with a specific disease or experiences a specific outcome during a defined period. It is particularly useful for studying outbreaks or the impact of specific exposures.
The formula for calculating the attack rate is straightforward:
Attack Rate = (Number of Cases in Exposed Population / Total Exposed Population) * 100
The result is typically expressed as a percentage. A higher attack rate indicates a more potent or easily transmissible agent, or a population that is more susceptible to the disease or outcome.
When to Use It:
Investigating foodborne or waterborne illness outbreaks.
Assessing the risk associated with exposure to an infectious agent.
Comparing the risk between different groups exposed to the same hazard.
Evaluating the effectiveness of preventative measures.
For instance, if 50 people out of a group of 500 who ate a particular dish became ill, the attack rate for that dish would be 10% (50/500 * 100). This suggests that the dish may have been contaminated.