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Streptococcal sore throat — strep throat for short — is one of the nastier maladies of childhood, causing fever, swollen tonsils, and the namesake sore throat. The bacterial infection can linger even after treatment, turning otherwise healthy children into carriers. 

“Around 8 to 10% of kids will stay colonized with strep even after the antibiotics are done,” said 91���� Associate Professor of Biological Sciences Laura Cook. “They no longer have symptoms. They feel healthy.”

Using whole genome sequencing, researchers from 91����’s Department of Biological Sciences, the University of Illinois at Chicago, and the University of Wisconsin School of Medicine and Public Health hope to discover why. Their article, “Streptococcus pyogenes carriage is associated with distinct in vivo transcriptional states but not carrier-specific genotypes,” was recently published in the journal Cell Reports.

Pediatricians at the University of Wisconsin collected samples from children who visited the clinic for strep throat; those who tested positive were enrolled in the study. The children were treated with antibiotics and then retested for the bacterial infection.

Once symptoms resolve, infections eventually clear, although children can carry strains of Group A Streptococcus (GAS) for months to years — and spread them to others. In cases of recurrent infections, children will often have their tonsils removed. Children without symptoms, however, are not typically tested to see if they function as carriers.

The genomes of the bacteria offered no clear indication as to whether those particular strains were more likely to cause an active infection or be carried without symptoms.

“That would point to the kids themselves — something about their immune response, or other bacteria in their throat that predispose them to be carriers,” said Cook, the article’s corresponding author.

The next step in their research: investigating other bacteria in children’s throats to see whether they play a role in strep persistence.

“We can compare the throat microbiota of healthy kids to those who are getting infections to see if we can predict or prevent carriage,” Cook said.