A large surveillance study showed that invasive group A streptococcal infections more than doubled in 10 U.S. states from 2013 to 2022, with certain populations facing substantially higher risk. Researchers documented concerning increases in incidence rates across multiple demographic groups and rising antimicrobial resistance.

In the population-based study, conducted through the Active Bacterial Core surveillance network, researchers identified 21,312 cases of invasive group A streptococcal infections (GAS) across 10 U.S. states during the 10-year surveillance period, including 1,981 deaths. Overall incidence increased from 3.6 per 100,000 persons in 2013 to 8.2 per 100,000 in 2022 (P < .001 for trend).

"The increasing invasive GAS burden, particularly among groups that have been economically and socially marginalized, requires urgent attention," the researchers wrote in JAMA.

The highest infection burden was seen in several specific populations:

• American Indian or Alaskan Native adults had incidence rates of 33.3 per 100,000—more than four times higher than rates among White (7.7 per 100,000) or Black (7.2 per 100,000) adults.
• People experiencing homelessness saw estimated incidence rates increase from 85.0 per 100,000 in 2013 to 806.7 per 100,000 in 2022.
• Long-term care facility residents experienced incidence rates of 101.1 per 100,000 in 2018.
• People who inject drugs had an estimated incidence rate of 97.0 per 100,000 in 2018.

Adults 65 years and older maintained the highest incidence rates throughout the study period, though the relative increase was greatest among adults aged 18 to 64 years, whose incidence nearly tripled from 3.2 to 8.7 per 100,000.

While pediatric cases showed no sustained trend, they notably decreased by 73% during the COVID-19 pandemic, from 2.0 per 100,000 in 2019 to 0.6 per 100,000 in 2021.

Among adults, clinical presentation was dominated by bacteremic cellulitis (44.6%), septic shock (19.2%), and bacteremia without focus (18.0%). The case fatality rate was 9.3% overall, increasing with age from 3.5% in persons aged 18 to 34 years to 21.9% in adults 85 years and older.

A particularly concerning issue noted by the study authors was rising antimicrobial resistance associated with invasive GAS infections. The proportion of isolates nonsusceptible to both macrolides and clindamycin increased from 12.7% in 2013 to 33.1% in 2022, though all isolates remained susceptible to β-lactam antibiotics and vancomycin.

The researchers also documented a changing landscape of invasive GAS strains. Formerly rare serotypes (emm types 43, 49, 60, 81, and 83) expanded significantly, collectively increasing from 0.3% of isolates in 2013 to 26.9% in 2022. During the COVID-19 pandemic, emm types primarily associated with pharyngeal infection declined while skin-associated types expanded.

"The increasing diversity of emm types was isolated from invasive GAS cases over time," the researchers noted. "Formerly rare serotypes, such as 43, 49, 60, 81, and 83, were responsible for approximately 40% of the increase in infections over the past 10 years."

The study authors emphasized that multiple factors likely contributed to rising incidence of invasive GAS infections, including the emergence and expansion of multiple bacterial lineages among at-risk populations rather than large outbreaks or clonal expansion of a single strain.

The study authors concluded: "Ongoing surveillance to monitor disease burden, strain distribution, and antimicrobial resistance is essential. Improved understanding of drivers of GAS transmission and increasing disease incidence could guide prevention and control efforts prior to availability of a licensed vaccine."

Disclosures can be found in the study.