Attack Rate Calculator
Understanding Attack Rate
The attack rate is a fundamental epidemiological measure used to describe the risk of contracting a specific disease within a population during a defined period. It is particularly useful in outbreak investigations to quantify the proportion of individuals who become ill after exposure to a particular infectious agent or a common source of infection.
The formula for attack rate is straightforward:
Attack Rate = (Number of Infected Individuals / Total Number of Exposed Individuals) * 100
The result is typically expressed as a percentage. A higher attack rate indicates a more potent or easily transmissible agent, or a more significant exposure event. Conversely, a lower attack rate suggests less infectivity or lower exposure levels within that specific group.
When is Attack Rate Used?
- Outbreak Investigations: To determine the likelihood of illness following exposure during an outbreak (e.g., foodborne illness, respiratory virus spread).
- Risk Assessment: To compare the risk of infection between different groups or after different exposure scenarios.
- Evaluating Interventions: To assess the effectiveness of control measures by comparing attack rates before and after implementation.
Example Calculation:
Imagine a community event where 500 people attended a picnic. Following the event, 75 individuals developed symptoms consistent with a foodborne illness.
Using the attack rate formula:
Attack Rate = (75 / 500) * 100 = 15%
This means that 15% of the individuals exposed at the picnic became ill. This information can help public health officials understand the severity of the outbreak and identify potential sources of contamination.