Secondary Attack Rate Calculator

Secondary Attack Rate Formula:

\[ \text{Secondary Attack Rate} = \frac{\text{Secondary Cases}}{\text{Contacts}} \times 100 \]

Secondary Attack Rate:

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1. What is Secondary Attack Rate?

Secondary Attack Rate (SAR) is an epidemiological measure that quantifies the frequency of new cases of a disease among contacts of known cases. It helps assess the transmissibility of infectious diseases in a population.

2. How Does the Calculator Work?

The calculator uses the Secondary Attack Rate formula:

\[ \text{Secondary Attack Rate} = \frac{\text{Secondary Cases}}{\text{Contacts}} \times 100 \]

Where:

Secondary Cases — Number of new cases among contacts
Contacts — Total number of exposed individuals at risk

Explanation: The formula calculates the percentage of contacts who develop the disease after exposure to primary cases.

3. Importance of Secondary Attack Rate

Details: SAR is crucial for evaluating infectious disease spread, effectiveness of control measures, and determining quarantine requirements. It helps public health officials make informed decisions about outbreak management.

4. Using the Calculator

Tips: Enter the number of secondary cases and total contacts. Both values must be non-negative integers, and contacts must be greater than zero for valid calculation.

5. Frequently Asked Questions (FAQ)

Q1: What constitutes a "secondary case"?
A: A secondary case is an individual who develops the disease after exposure to a primary (index) case during the infectious period.

Q2: How is SAR different from basic reproduction number (R0)?
A: SAR measures transmission in a specific exposed group, while R0 estimates average number of secondary cases from one infected individual in a fully susceptible population.

Q3: What factors can affect SAR?
A: SAR can be influenced by disease characteristics, contact patterns, preventive measures, population immunity, and environmental factors.

Q4: When is SAR most useful?
A: SAR is particularly valuable for studying household transmission, healthcare settings, and closed populations where contact tracing is feasible.

Q5: What are typical SAR values for common diseases?
A: SAR varies widely by disease. For example, measles has high SAR (75-90%), while SARS typically shows lower rates (10-20%) depending on control measures.