Molecular methods enhance the detection of pyoderma-related Streptococcus pyogenes and emm-type distribution in children

Background

Streptococcus pyogenes–related skin infections are increasingly implicated in the development of rheumatic heart disease (RHD) in lower-resource settings, where they are often associated with scabies. The true prevalence of S pyogenes–related pyoderma may be underestimated by bacterial culture.

Methods

A multiplex quantitative polymerase chain reaction (qPCR) assay for S pyogenes, Staphylococcus aureus, and Sarcoptes scabiei was applied to 250 pyoderma swabs from a cross-sectional study of children aged <5 years in The Gambia. Direct PCR-based emm-typing was used to supplement previous whole genome sequencing (WGS) of cultured isolates.

Results

Pyoderma lesions with S pyogenes increased from 51% (127/250) using culture to 80% (199/250) with qPCR. Compared to qPCR, the sensitivity of culture was 95.4% for S pyogenes (95% confidence interval {CI}, 77.2%–99.9%) in samples with S pyogenes alone (22/250 [9%]), but 59.9% (95% CI, 52.3%–67.2%) for samples with S aureus coinfection (177/250 [71%]). Direct PCR-based emm-typing was successful in 50% (46/92) of cases, identifying 27 emm-types, including 6 not identified by WGS (total 52 emm-types).

Conclusions

Bacterial culture significantly underestimates the burden of S pyogenes in pyoderma, particularly with S aureus coinfection. Molecular methods should be used to enhance the detection of S pyogenes in surveillance studies and clinical trials of preventive measures in RHD-endemic settings.