Incidence of invasive group A streptococcal infections and comparison of emm types from invasive infections, pharyngitis, and throat carriage in American Indian communities in the Southwest United States.

BACKGROUND

American Indian/Alaska Native (AI/AN) communities in the US have high rates of group A streptococcal (GAS) infections. We determined the incidence of invasive infections in AI communities in the Southwest and compared emm types from invasive infections, pharyngitis, and throat carriage.

METHODS

Activities conducted in the White Mountain Apache Tribal lands (WMA) and Navajo Nation (NN) included active, laboratory-based surveillance for invasive GAS infections (WMA: 2019─2024; NN: 2023─2024; all ages); surveillance for GAS pharyngitis (2023-2024; children 0─17 years); and culture for GAS from oropharyngeal carriage samples (2019 and 2022─2023; children 0─14 years). Emm types were determined by whole-genome sequencing. Annual incidence rates were calculated using Poisson regression.

RESULTS

In WMA, age-standardized rates of invasive infections ranged from 80-270/100,000 persons between 2019-2024. Predominant emm types varied (n=74 isolates): 91 (59%) and 49 (32%) in 2019-2020, and 43 (40%) and 53 (30%) in 2023. In NN, rates were 40-60/100,000 persons in 2023-2024; common emm types (n=51) were 53 (28%), 101 (18%), and 12 (16%). In WMA and NN, emm types 1, 12, and 53 predominated in pharyngitis (n=190), and 1, 12, and 91 in throat carriage (n=119).

CONCLUSIONS

Rates of invasive GAS infections in these communities were 3-35 times higher than the national US average (12.2/100,000 in 2024). Emm types varied over time with limited overlap in strains from throat carriage or pharyngitis isolates and those from invasive infections. Findings support continuing GAS surveillance and engaging AI/AN communities throughout vaccine development and evaluation.