Streptococcus dysgalactiae as a cause of peripartum infections - a population-based cohort study with phylogenetic analysis of hospital clusters.

Purpose: We aimed to investigate the incidence and clinical features of Streptococcus dysgalactiae peripartum infections (SDPI), and to investigate the distribution of emm-types in relation to disease severity and the genetic relatedness of isolates from hospital clusters.

Materials and methods: Patients with growth of S. dysgalactiae in a genital or wound culture, collected between January 2014 and September 2020 at departments for gynecology and obstetrics, were identified. For inclusion, patients had to be pregnant, or given birth, or undergone an abortion within 42 days prior to debut of symptoms. All isolates had previously been emm-typed. A cluster was defined as two or more patients with S. dysgalactiae of the same emm-type admitted to the same hospital within a 30-day period. The cluster isolates were subjected to whole genome sequencing (WGS).

Results: The final study cohort comprised 130 patients. The incidence of S. dysgalactiae postpartum infection was approximately 1 case/1000 births. The patients fulfilled criteria for endometritis (n = 94), postpartum fever (n = 15), wound infection (n = 8) or chorioamnionitis (n = 4). Most patients with endometritis (87%) had onset of symptoms > 48 h post-partum. The most common emm-type was stG62647 (n = 41). Thirteen hospital clusters were identified, of which only three had bacterial isolates that were closely genetically related (0-6 SNP).

Conclusion: Our findings demonstrate that SDPI impact a relatively large number of patients. No patient was critically ill, but the morbidity appeared to be substantial. Hospital outbreaks of SDPI are rare, but when suspected, WGS should be employed to investigate relatedness between isolates.