The Centers for Disease Control and Prevention is warning of an increase in severe infections involving the Group A streptococcus bacteria, also known as Strep A, among children.

There has been a “recent increase in pediatric invasive group A streptococcal (iGAS) infections,” the CDC said Thursday in a health advisory to clinicians and public health authorities, adding that in some cases the rise has “occurred in the setting of increased circulation of respiratory syncytial virus (RSV), influenza viruses, SARS-CoV-2, and other respiratory viruses.”

While the overall number of cases has remained relatively low and iGAS infections are rare in children, the CDC said it would be investigating reports of increased cases in states including Colorado.

Strep A is highly contagious but not generally life-threatening with the bacteria commonly carried by many people in their nose, throat and skin. Strep A symptoms are often flu-like and mainly include “strep throat” – a mild but painful infection. Most people with Strep A recover without any complications.

However, in rare instances cases can develop into infections known as invasive group A strep (iGAS), which can be fatal, with the risk greatest among children and the elderly.

It occurs when bacteria goes deeper into the body, infecting the lungs, muscles and bloodstream, and potentially causing more severe illnesses such as blood infections, endocarditis (an infection of the heart’s inner lining) and meningitis.

At least two children in Colorado have died of iGAS, as have 21 children in the United Kingdom.

The Streptococcal bacteria is spread through coughing, kissing, sneezing and touching, from someone with an infection or a carrier. Outbreaks are more frequent in facilities like schools and care homes where close contact is common.

Teaching children good hand washing hygiene can help prevent the spread, say health experts, as well as covering their mouths when coughing or sneezing or using alcohol-based hand sanitizer before eating and at other times.

There is no Strep A vaccine available. Most cases are treated with a course of antibiotics.

“Keeping up to date on vaccines for COVID-19, flu, and chickenpox can help protect your child from developing complications from a group A strep infection,” Rachel Herlihy, state epidemiologist at the Colorado Department of Public Health and Environment (CDPHE), said in a statement this month.

“Stay home when you are sick and practice good hand hygiene … call your child’s doctor if they are experiencing new or worsening symptoms of an illness.”

The CDC, in its latest advisory, recommended members of the public learn about the symptoms of serious infections caused by Group A Strep, including necrotizing fasciitis, streptococcal toxic shock syndrome and cellulitis, and seek medical care quickly if they think they are affected.

The Colorado Department of Public Health and Environment reported an uptick of iGAS cases in November, with ages ranging from 10 months to 6 years – although the department stressed that anyone of any age can get group A strep.

In Minnesota, health officials said they had seen 46 cases of invasive strep A in all ages in November, more than double the average 20 cases in previous months. Texas Children’s Hospital said it has seen more than 60 patients with invasive strep A in October and November – a fourfold increase from the same period the previous year.

Cases are also spreading in Europe. France, Ireland, the Netherlands, Sweden and the United Kingdom have all reported cases, according to the World Health Organization, with children under age 10 most impacted.

“Enhanced surveillance activities have been implemented in the countries reporting an increase in iGAS cases,” it said this month. “An alert has been issued to other countries to be vigilant for a similar rise in cases and to report any unexpected increased national or regional incidence of iGAS infections to WHO.”

The disease is responsible for more than 500,000 deaths annually worldwide, according to WHO. However, in general, the public health body said the risk to the general population remains “low.”

England has reported 94 deaths across all age groups, including 21 children, from invasive Strep A, the U.K. Health Security Agency (UKHSA) said this week, reporting a “higher number of cases than seen in a typical year.” In France, at least two people have also died.