Europe is seeing a concerning number of severe Strep A cases and deaths, the World Health Organization said Thursday, warning other countries to be on the lookout for a similar pattern.
The U.S. Centers for Disease Control and Prevention is also looking into a "possible increase" in such cases among children, according to the agency's website.
A higher-than-usual number of invasive Strep A cases—some leading to scarlet fever, and often in children under 10—has already been seen this season in France, Ireland, the Netherlands, Sweden, the U.K., and Northern Ireland, according to a situation report released Thursday by the WHO.
"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" to the international health agency, the report stated.
Strep A season may be off to an early start, the report noted.
RSV and flu are also off to early and severe starts this year, circulating at epidemic levels in the U.S. and abroad. Combined with the COVID pandemic, public health experts are calling the phenomenon a "tripledemic." But there are more than three pathogens are circulating at increased levels this fall. Influenza-like illnesses like rhinovirus and enterovirus, in addition to Strep A, are among those being seen more frequently.
Respiratory viruses can lead to a co-infection with Strep A, according to the WHO. So, an uptick in such viruses like the one we're seeing now could lead to an uptick in Strep A cases.
Group A Streptococcal infections usually lead to mild illness like tonsillitis, pharyngitis, impetigo, and cellulitis. But when Strep A, a bacteria, infects areas of the body that are usually sterile—like blood, deep muscles, fat, and the lungs—it can cause a more severe illness known as invasive Strep A, which can be deadly.
In some countries, the uptick in invasive Strep A infections has occurred since the spring but has become worse this fall, according to the WHO.
In Ireland, 23 cases have been reported since October, compared to 11 cases in 2019, before the pandemic. In the Netherlands, cases began increasing in March, and some patients have also had co-infections with respiratory viruses and varicella zoster, a herpes virus that can cause chickenpox and shingles. And Sweden has seen 93 cases since October, compared to seven cases during the same span in 2018, and 10 cases during the same span in 2019, the agency noted.
England saw higher-than-usual levels of scarlet fever this summer, and is now receiving reports of nearly four times more scarlet fever patients than usual, with 4,622 cases reported in a recent six-week period. Scarlet fever outbreaks are being reported in daycares and schools, according to the UK Health Security Agency. The country had seen 13 related deaths this season as of Dec. 8, compared to four deaths during the same period in 2017 and 2018.
U.S. cases on the rise in some locations
The CDC did not respond to Fortune's request on Thursday for information on the circulation of Strep A cases in the U.S., or to a similar request sent 10 days ago. When questioned on the topic at a Dec. 5 press conference, federal health officials said they had no information about recent U.S. Strep A cases readily available.
Anecdotally, however, cases appear to be on the rise in the U.S.
Johns Hopkins Children's Center in Maryland is seeing group A strep infections this fall, in addition to other invasive bacterial infections stemming from ear infections and sinus infections, pediatric infectious disease specialist Dr. Aaron Milstone told Fortune in a statement.
"Given the very high rates of viral infections this fall, we would expect to see more complications," he said, adding that the hospital isn't yet sure if the percentage of children with invasive bacterial infections this season is greater than usual, or if a higher number of invasive bacterial infections is simply being seen due to the increased circulation of respiratory viruses.
Pediatric hospitals in Arizona, Colorado, Texas, and Washington are seeing higher-than-average numbers of invasive Strep A infections this fall, NBC News reported Wednesday.
This is a developing story and will be updated.