Preceding group A streptococcus skin and throat infections are individually associated with acute rheumatic fever: evidence from New Zealand.

INTRODUCTION: Acute rheumatic fever (ARF) is usually considered a consequence of group A streptococcus (GAS) pharyngitis, with GAS skin infections not considered a major trigger. The aim was to quantify the risk of ARF following a GAS-positive skin or throat swab.

METHODS: This retrospective analysis used pre-existing administrative data. Throat and skin swab data (1 866 981 swabs) from the Auckland region, New Zealand and antibiotic dispensing data were used (2010-2017). Incident ARF cases were identified using hospitalisation data (2010-2018). The risk ratio (RR) of ARF following swab collection was estimated across selected features and timeframes. Antibiotic dispensing data were linked to investigate whether this altered ARF risk following GAS detection.

RESULTS: ARF risk increased following GAS detection in a throat or skin swab. Māori and Pacific Peoples had the highest ARF risk 8-90 days following a GAS-positive throat or skin swab, compared with a GAS-negative swab. During this period, the RR for Māori and Pacific Peoples following a GAS-positive throat swab was 4.8 (95% CI 3.6 to 6.4) and following a GAS-positive skin swab, the RR was 5.1 (95% CI 1.8 to 15.0). Antibiotic dispensing was not associated with a reduction in ARF risk following GAS detection in a throat swab (antibiotics not dispensed (RR: 4.1, 95% CI 2.7 to 6.2), antibiotics dispensed (RR: 4.3, 95% CI 2.5 to 7.4) or in a skin swab (antibiotics not dispensed (RR: 3.5, 95% CI 0.9 to 13.9), antibiotics dispensed (RR: 2.0, 95% CI 0.3 to 12.1).

CONCLUSIONS: A GAS-positive throat or skin swab is strongly associated with subsequent ARF, particularly for Māori and Pacific Peoples. This study provides the first population-level evidence that GAS skin infection can trigger ARF.