About Group A Strep Calculator

Group A Streptococcus (GAS) can cause mild illnesses, such as strep throat and impetigo (a skin infection), as well as life-threatening illnesses, such as necrotizing fasciitis (sometimes called the "flesh-eating disease") and streptococcal toxic shock syndrome. When GAS infects internal organs and tissues, such as blood, muscle or lungs, it is referred to as an invasive GAS infection.

Clusters of invasive GAS infections in a community or institution can create anxiety among health care providers and the public. Local or state health agencies may investigate these clusters to determine if the cases are linked to common exposures or if they occur in closed populations such as nursing homes or military facilities. If cases are linked to common exposures or occur among closed populations, urgent public health action may be indicated. See Starting an investigation for more information.

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.

This website includes an interactive calculator designed to answer the question "what number of invasive GAS infections would normally be expected in a given month for a similar county or region?" The calculator uses the characteristics of the county or region and national data on invasive GAS incidence to provide the expected number of cases. Public health officials may compare the expected number of cases to the number in the cluster under investigation. See Using the calculator.

The calculator was not designed to establish links between invasive GAS cases or for use in investigations of clusters in closed populations such as nursing homes or military facilities.