“While the overall number of cases has remained relatively low and iGAS infections remain rare in children, CDC is investigating these reports,” the advisory reads. 

Group A strep (streptococcus) is a bacteria that can cause several infections, including strep throat which affects the throat and tonsils and is most common in those ages 5 to 15, although adults can also get infected.

Invasive strep A occurs when the infection spreads to other parts of the body like the bloodstream. It can cause severe problems such as cellulitis, a bacterial skin infection, and toxic shock syndrome, which can cause low blood pressure and organ failure. 

While experts don’t know the specific reason for the increase in invasive strep cases, Dr. Glenn Fennelly, a professor and chair of pediatrics at the Texas Tech Physicians of El Paso, tells Fortune. It may be because new more invasive strains of strep A have been introduced into certain communities, and can spread easily since many pandemic safety measures have been lifted. 

In some cases, the infections have been reported in areas that have an increase in COVID-19, RSV, and influenza cases, the CDC says in their health advisory. 

“Infectious diseases come in waves,” Dr. David Hill, a hospitalist pediatrician for Goldsboro Pediatrics in North Carolina, tells Fortune. “I don’t find it particularly surprising or alarming, but it is certainly something that parents should be aware of.”

What are the symptoms of strep throat and invasive strep A?

Strep throat presents with the following symptoms, according to the CDC: 

• Sore throat that can happen abruptly 
• Pain after swallowing
• Swollen lymph nodes in the front of the neck
• Small red spots on the roof of the mouth
• Fever 
• Red and swollen tonsils 

It is not common to have a runny nose, congestion, or cough when infected with strep throat. If you have a sore throat and a fever, you’re more likely to have strep throat than if you have a sore throat with a cough or congestion. 

These symptoms may indicate an invasive strep A infection: 

• Fever
• Behavior changes
• Feeling weak
• Muscle aches and swelling
• Vomiting 
• Presence of a rash 

How is strep throat treated?

An official test in a doctor’s office or urgent care is the best way to know if treatment for strep is warranted. 

Antibiotics are used to treat strep throat. When prescribed antibiotics, Hill says it’s important to take the full course even if symptoms go away to prevent rheumatic fever, a serious potential outcome of untreated strep throat in children. Oral amoxicillin, the most commonly used antibiotic for strep throat, is facing a shortage that “is anticipated to last several months,” according to the American Academy of Pediatrics. 

“Oral amoxicillin is sort of considered first line medication and most palatable—is absorbed well,” Fennelly says. “In the absence of that availability, doctors have been resorting to using either oral or injectable penicillin, or an antibiotic called cephalexin.” 

Strep throat can be transmitted through saliva, so experts say monitor children’s habits and avoid openly sharing beverages, food or silverware, and encourage handwashing. It can also be spread through respiratory droplets from coughing and sneezing. 

Using anecdotal evidence, many cases of invasive strep A develop after a child is infected with the flu, Fennelly says, so continuing to vaccinate against influenza is an important measure.