Streptococcus anginosus group as a cause of serious streptococcal infection in the UK: a retrospective...

Despite emerging evidence indicating an increasing burden of invasive Streptococcus anginosus group (SAG) intracranial infections in children, their wider epidemiology remains inadequately explored. We aimed to describe the epidemiology of SAG infections in adults and children in the UK.

We conducted a retrospective population-based surveillance study of microbiological laboratory samples, including all samples from which Streptococcus spp were identified, at Great Ormond Street Hospital (GOSH; London, UK), which processes local paediatric and national specimens from all ages, from Jan 1, 2000, to Dec 31, 2023, and at University College London Hospitals (UCLH; London, UK; all ages), from Jan 1, 2012, to Dec 31, 2023. Samples with missing data were excluded. We also analysed the nationally reported streptococcal bacteraemia data from Jan 1, 2015, to Dec 31, 2023, and calculated the annual rates of SAG sterile body site (SBS) infections per 1000 emergency admissions at each hospital. Temporal trends were analysed using negative-binomial regression with admission numbers as an offset. Descriptive statistics summarised infection characteristics by organism, species, body site, age, and sex. National bacteraemia trends were analysed relative to population denominators. Analyses included only records with complete routine laboratory data, and samples without sufficient information were excluded from relevant subgroup analyses.

As we only included routinely collected laboratory data, comprehensive demographic and ethnicity data were not available. The median age of patients from whom Streptococcus spp of interest (SOI) were isolated was 44·41 years (IQR 12·327-64·32). 2215 (59·8%) of 3702 patients with SOI SBS infection (defined as an infection of an anatomical area expected to be devoid of microorganisms) were male. At both GOSH and UCLH, incidence of SAG sterile body site infections increased year-on-year from 2·12 per 1000 emergency hospital admissions in 2012 to 11·51 per 1000 emergency hospital admissions in 2023 at GOSH (p<0·0001) and from 0·97 per 1000 emergency hospital admissions in 2012 to 6·04 per 1000 emergency hospital admissions in 2023 at UCLH (p<0·0001). SAG diagnoses in external samples, which were referred to GOSH for molecular diagnostics, also increased markedly over time compared with other Streptococcus spp diagnoses. In all groups, SAG is the current dominant cause of streptococcal sterile body site infection. SAG sterile body site infections most frequently involved the CNS (222 [19·6%] of 1133), especially in children (87 [39·2%] of 222), intrathoracic sites (283 [24·9%] of 1133), and abdominal sites (202 [17·8%] of 1133). At the species level, all three SAG species contributed to the increase in infections. S intermedius was the dominant cause of CNS and intrathoracic infections, whereas S anginosus and S constellatus were the dominant causes of abdominal infections.

SAG infections, predominantly deep pyogenic collections in SBSs, are increasing in both children and adults in the UK and represent a major cause of streptococcal SBS infections. This increase is unlikely to be explained solely by improved diagnostics or increased sampling and suggests a real change in epidemiology. Further work is urgently needed to understand whether this change is because of increasing virulence of SAG organisms, changes in carriage rates or dynamics, or the presence of alternative drivers.

The European Society of Clinical Microbiology and Infectious Diseases (Europäische Gesellschaft für klinische Mikrobiologie und Infektionskrankheiten; ESCMID).