It’s not just droplets: a systematic review and meta-analysis of the modes of transmission of Group A Streptococcus

Background The transmission of Group A Streptococcus (Strep A) through respiratory droplets has been considered the dominant mode of transmission to date; however, little is known about the relative contribution of other modes of transmission. This review systematically summarises the contemporary evidence regarding the transmission of Strep A. Methods A comprehensive search strategy was implemented to identify studies on Strep A transmission published in English between 1980 and 2019. Full-text articles were screened and included based on the predefined criteria. Studies were included if molecular techniques were used to identify the same Strep A strain in both clinical and environmental swabs. A random-effects meta-analysis model was used to aggregate attack rate estimates with 95% confidence intervals (CI), incorporating the Freeman–Tukey transformation to account for variability between studies. Results A total of 34 transmission cohorts were included in this study. The overall attack rate of Strep A was 18.4% (95% CI, 13.1–24.2%, I 2 = 95.9%), for direct contact, it was 20.5% (95% CI, 8.3–35.4%), and for indirect contact, it was 19.1% (95% CI, 13.2–25.7%). When pooled by geographical location, the attack rate was 30.38% (95% CI, 20.89–40.75%) in non-urban settings and 7.36% (95% CI, 2.60–14.21%) in urban settings. Conclusion Direct contact is no longer the dominant form of Strep A transmission. Our contemporary findings have implications for the development of evidence-based environmental health strategies aimed at reducing Strep A transmission. Systematic review registration https://www.crd.york.ac.uk/PROSPERO/view/CRD42019138472 , CRD42019138472.