Strep is on the rise in the US. While invasive group A strep infections once remained at a stable rate for 17 years, that’s no longer the case.

According to a study from the Centers for Disease Control and Prevention published in the Journal of the American Medical Association, the number of invasive group A strep infections more than doubled between 2013 and 2022.

Though the bacteria group A streptococcus is what causes strep throat, invasive strep is not your run-of-the-mill illness. Instead, the more serious sickness occurs when bacteria spreads to places like the lungs and bloodstream.

That can cause complications including necrotizing fasciitis and streptococcal toxic shock syndrome. The former is a flesh-eating disease, while the latter can lead to organ failure.

Dr. Victor Nizet, a professor of pediatrics at the University of California, San Diego, told NBC News that patients with invasive strep have a “very, very rapid deterioration” over one to two days. What begins “seeming like a routine flu-like illness” can end with a patient in the ICU “fearing for their recovery,” he said.

The study, which looked at 35 million people across 10 states, found more than 21,000 cases of the infection, including nearly 2,000 deaths. 

Why Invasive Strep Is Becoming More Prevalent

As for why invasive strep is on the rise, the study theorized that rising rates of obesity, diabetes, and types of strains could be to blame. The latter cause also means invasive strep is becoming harder to treat with antibiotics, leading to more serious cases.

The people most feeling the rise of invasive strep are those over 65, American Indian or Alaska Native persons, residents of long-term care facilities, people experiencing homelessness, and people who inject drugs, the study found.

The study warned that accelerated efforts to prevent and control invasive steps are needed, especially among groups at highest risk of infection.