It is one of the deadliest bacterial infections in the United States, and most Americans have never heard its clinical name. Invasive Group A Streptococcus — or iGAS, caused by Streptococcus pyogenes, the same bacterium responsible for strep throat and scarlet fever — kills approximately 2,000 Americans every year in its systemic, tissue-destroying form. Between 2022 and 2023, it reached a 20-year high in the United States. And a major surveillance study published in the CDC's Emerging Infectious Diseases journal in June 2026 confirms that one of its most dangerous amplification points is a setting that is expanding in every major American city: large congregate homeless shelters.
The study documents a cluster of 41 confirmed iGAS cases at a single large Chicago shelter between October 2023 and January 2024 — an outbreak that resulted in 2 deaths and required coordinated public health emergency response. Whole-genome sequencing confirmed that 38 of the 41 cases were caused by a single dominant strain of Streptococcus pyogenes, meaning the bacterium spread from person to person within the shelter rather than representing coincidental individual exposures. The median age of affected individuals was 51 years. Underlying conditions, including alcohol use disorder, injection drug use, wounds, and skin breakdown, were common in those who developed invasive disease.
