Invasive group A streptococcal infections in North West England: epidemiology, risk factors and fatal infection.

OBJECTIVES: In England, notifications of invasive group A streptococcal (iGAS) infections have increased since 2015. We describe time trends, risk factors, as well as clinical and infection characteristics amongst iGAS cases in North West England, focussing on people who inject drugs (PWIDs), prisoners and homeless populations (referred to as risk groups), and analyse factors for fatal infection. STUDY DESIGN: The study design used was a cross-sectional study. METHODS: Data for all iGAS cases notified to Public Health England North West between January 2016 and May 2019 were used. Analysis consisted of time trend analysis, descriptive statistics, hypothesis testing to investigate differences in clinical and infection characteristics between risk and non-risk groups and binary logistic regression to identify factors associated with fatal infection. RESULTS: There were 1353 cases. Two hundred and two were amongst risk groups, who were predominantly PWIDs in Greater Manchester. Soft tissue risk factors were widespread. There were differences in strain-type between risk and non-risk groups. Female gender, cancer, emm1.0 and emm5.23 were associated with increased odds of death, whilst cellulitis was associated with reduced odds. The relationship between age and death was U-shaped. CONCLUSIONS: iGAS has increased in North West England since 2016, including amongst PWIDs. This may be due to emm-type replacement, barriers to good hygiene and increasing colonisation.