Descriptive analysis of group A Streptococcus in skin swabs and acute rheumatic fever, Auckland, New Zealand, 2010–2016

BACKGROUND: Group A Streptococcus (GAS) can trigger an immune-mediated response resulting in acute rheumatic fever (ARF). Historically, ARF has been considered a consequence of preceding GAS pharyngitis, but increasing evidence suggests that GAS skin infections may be a driver. Data on the primary care burden of GAS skin infection are limited. This paper aims to describe and compare the prevalence and distribution of GAS detection in skin swabs and ARF rates in the Auckland population. METHODS: This cross-sectional study used all laboratory skin swab data from people who had a skin swab taken as a result of a consultation with a health professional in the Auckland region (2010–2016). Initial primary hospitalisations for ARF were identified and all data were linked using unique patient identifiers to patient's age, prioritised ethnicity, sex, and socio-economic status. FINDINGS: 377,410 skin swabs from 239,494 individuals were included. 12·8% of swabs were GAS positive, an annual incidence of 4·8 per 1,000 person-years. Māori and Pacific Peoples under 20 years of age had markedly higher GAS detection in skin swabs (RR 4·0; 95% CI 3·9–4·2: RR 6·8; 95% CI 6·6–7·0) and significantly higher ARF rates (RR 30·3; 95% CI 19·5–46·9: RR 69·7 95% CI 45·8–106·1) compared with European/Other ethnicities. INTERPRETATION: The observation that GAS detection was markedly higher in Māori and Pacific Peoples provides a potential explanation for the marked ethnic differences in ARF. These findings support a greater focus on addressing the burden of skin infection in NZ, including as ARF prevention. FUNDING: The first author received a training stipend from the New Zealand College of Public Health Medicine (NZCPHM) during her Masters of Public Health.