(NewsNation) — Hospitals are seeing an alarming rise in cases of severe and potentially deadly strep throat in kids.

Strep throat is caused by the Group A streptococci bacteria, which can also cause scarlet fever and impetigo. Common in children, these illnesses are usually treated successfully with antibiotics.

In rare cases, however, the infection can move into the bloodstream, causing invasive strep. Once in the bloodstream, the bacteria can cause infections including pneumonia, toxic shock and necrotizing fasciitis, and may be deadly.

The United Kingdom issued a health warning after at least 15 children died from invasive strep. Hospitals in the U.S. are also reporting more cases of invasive strep than usual this year.

In Colorado, two children died from invasive strep. Children’s hospitals in the state are reporting higher numbers of invasive strep this year, as are hospitals in Arizona, Texas and Washington.

People with chronic illnesses and those over 65 are usually most at risk for invasive strep. Health officials are trying to determine why there is an uptick among children this year. One possible reason could be the influx of respiratory viruses, including COVID-19, the flu, and RSV, which are circulating this year. If those viruses weaken the immune system, it could be making it easier for strep A bacteria to pass into the bloodstream.

“Viral infections can predispose to severe bacterial infections,” said Dr. Monica Gandhi, professor of medicine at University of California, San Francisco. COVID-19, the flu and RSV are all viral infections, while strep is a bacterial infection.

The best way to prevent strep throat is to wash hands often, stay away from people who are sick and avoid sharing food and drinks. Symptoms of strep include a sore throat, pain when swallowing, fever, swollen lymph nodes and swollen tonsils.

Symptoms of invasive strep can vary, but may include high fever, muscle aches, nausea and vomiting, diarrhea, difficulty breathing and redness or swelling of the skin.

If you suspect you or your child has strep, make an appointment with a doctor or urgent care center. If you believe you or a loved one is showing symptoms of invasive strep, seek medical help immediately.