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Woman on PCThe interactive calculator will provide an estimate of the number of invasive group A streptococcal (GAS) disease cases that might be expected in a given month in a county or region with characteristics that you specify. Enter the month of interest, the number of invasive GAS infections in that month and the previous month, the average temperature of your state during the previous month, characteristics of your county/region, including population and area in square miles, and factors related to the risk of invasive GAS infection, such as the prevalence of HIV-infection and injection drug use among GAS cases in your area. The population of the area must be 250,000 persons or larger; smaller counties may be combined.


Calculate Invasive GAS Cases for Your Community

Group A Strep Calculator

Calculator to estimate expected number of invasive group A streptococcus cases in county or region.


This website was developed to help local and state health departments evaluate possible increases of unrelated cases of GAS infection. For others using this website, please contact your local or state health department if you are concerned about a cluster of GAS infections.

How the Calculator was Developed

The calculator is based on a regression model of data from CDC's Active Bacterial Core surveillance (ABCs), an active, population-based surveillance system for invasive group A streptococcal infections. The model used data collected from 1989 through 2002 from diverse populations in 9 states (CA, CO, CT, GA, MD, MN, NY, OR, TN), including over 50 regions ranging in size from 250,000 to 1.3 million persons. The calculator estimates the average number of invasive GAS cases expected during a one month period in a region with given population characteristics.