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<h3>Background</h3> Group B streptococcus (GBS) is the most common cause of sepsis and meningitis in infants <90 days old in the UK. In 2020 increased rates of invasive GBS (iGBS) were noted in infants at a district general hospital in the East of England. A multi-disciplinary review was conducted to try to identify reasons for this increase, and to determine whether systems changes due to the COVID-19 pandemic may have played a role. <h3>Objectives</h3> Investigation of a local increase in invasive GBS cases in infants. <h3>Methods</h3> A retrospective case note review of all cases of iGBS occurring between 2015 and 2020 was conducted. Cases occurring in 2020 were compared to cases in 2015–2019 and to a matched-control population for presence of known risk factors and demographics, Whole genome sequencing was conducted on bacterial isolates from cases in 2020 in order to identify whether the increased incidence represented an outbreak. <h3>Results</h3> In 2020 14 cases of iGBS occurred in infants <90 days of age (Incidence rate (IR) 2.55/1000); 5 Early Onset GBS (EOGBS, 0–6d, IR 0.91/1000)) and 9 Late Onset GBS (LOGBS, 7–89d, (IR 1.64/1000)) at our hospital. These rates were 1.2-fold and 4.5-fold higher, respectively, than the local rates for 2019, and 1.7-fold and 5.5-fold higher than the 2019 national rates. All babies with EOGBS in 2020 had identifiable risk factors; 4/5 had maternal pyrexia >38°C, 1/5 had suspected chorioamnionitis and 3/5 had prolonged rupture of membranes >18 hours. All received appropriate intra-partum antibiotics. GBS colonisation was unknown prior to delivery in any mother, with 60% of mothers in 2020 subsequently testing positive compared to 27% in 2015–2019. There were no significant differences in the demographics of infants with EOGBS in 2020 compared to 2015–2019. All cases of EOGBS in 2020 were identified rapidly following delivery, and treated according to NICE guidelines. Cases of LOGBS in 2020 tended to occur more in low risk, term deliveries compared to previous years. In 2020 43% of infants with LOGBS had no identifiable risk factors for LOGBS at delivery, compared to 23% in the early time-period. Infants with LOGBS in 2020 were demographically comparable to those in 2015–2019. No clear evidence of an impact of the COVID-19 pandemic was found. Mothers of infants with LOGBS disease had slightly fewer antenatal microbiological samples, where GBS may have been identified incidentally, compared to previous years (56% vs. 75%), possibly indicating reduced ad-hoc presentations as a result of the pandemic, although this difference was not significant. No evidence for nosocomial or community clustering of cases was found. Whole genome sequencing identified serotype III ST-17 as the dominant GBS strain. However, isolates were genomically diverse with no evidence of an outbreak of a hyper-virulent strain. All sequenced isolates carried the mreA gene conferring macrolide resistance. <h3>Conclusions</h3> An increase in LOGBS cases in our low-risk term-infant population was noted during 2020, with high rates of iGBS strains showing macrolide resistance. No clear evidence for an outbreak of a virulent strain, or impacts of the COVID-19 pandemic was found.