Management of an outbreak of postpartum Streptococcus pyogenes emm75 infections

Background: Streptococcus pyogenes is a well-known cause of postpartum infections and is causing significant morbidity and mortality. Aim: To describe measures taken to control an outbreak of postpartum infections caused by S. pyogenes emm75 on a maternity ward. Methods: Patients presenting postpartum with signs and symptoms of infection were cultured for β-haemolytic streptococci with cervical swabs and blood cultures, and bacterial isolates were species-determined with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and emm-typed. Pharyngeal swabs were taken from healthcare workers (HCWs) at the ward. Bacterial isolates were subjected to whole-genome sequencing (WGS). The multi-locus sequence type and the number of single nucleotide polymorphisms (SNPs) compared to an index genome were determined. Findings: During a three-month period, six cases of postpartum infection with S. pyogenes emm75 were identified on the maternity ward. By comparing delivery dates with duty rotas, one HCW was identified as a possible source of infection in five cases. After repeated pharyngeal swabs from this individual, an S. pyogenes emm75 was isolated. The five isolates from patients epidemiologically linked to the HCW and the two isolates of the family members had an identical sequence type (ST49) and 0–2 SNPs difference compared to the HCW isolate, whereas the sixth patient had an unrelated isolate. Eradication antibiotic therapy with clindamycin and rifampicin was given to the carrier. All patients received intravenous antibiotic treatment and recovered. Conclusion: A three-month outbreak was stopped when a carrier was identified and treated. Source identification and WGS proved vital for outbreak control