It's not just droplets: A systematic review and meta-analysis of modes of transmission of group A Streptococcus

Dylan D Barth^1*Jessica Daw¹Stephanie L Enkel¹Tracy Mcrae¹Jonathan R Carapetis^1,2Rosemary Wyber^1,3Asha C Bowen^1,2Mark E Engel⁴

• ¹Wesfarmers Centre of Vaccines & Infectious Diseases, Telethon Kids Institute, University of Western Australia, Nedlands, Australia
• ²Department of Infectious Diseases, Perth Children’s Hospital, Perth, Western Australia, Australia, Perth, Australia
• ³The George institute for Global Health, Sydney, Australia
• ⁴SA Cochrane Centre, South African Medical Research Council, Francie van Zijl Dr, Parow Valley 7501, South Africa, Cape Town, South Africa

Transmission of Group A Streptococcus (Strep A) via droplets has been the dominant transmission paradigm to date, but little is known about the relative contribution of other modes of transmission. We aimed to systematically summarise contemporary evidence of Strep A transmission. Using a comprehensive search strategy to identify Strep A transmission studies published in English between 1980 and 2019, full-text articles were identified and included against predefined criteria. Studies were included if molecular techniques were used to identify the same strain of Strep A in both clinical and environmental swabs. We used the random effects meta-analysis model to aggregate attack rate estimates with 95% confidence intervals (CI) and incorporated the Freeman-Tukey transformation to account for between study variability. Thirty four transmission cohorts were included. The overall Strep A attack rate was 18.4% (95% CI, 13.1% to 24.2%, I 2 = 95.9%), for direct contact 20.5% (95% CI 8.3% to 35.4%) and indirect contact 19.1% (95% CI 13.2% to 25.7%). Pooled attack rates by geographical location was 30.38% (95% CI 20.89% to 40.75%) in non-urban settings and 7.36% (95% CI 2.60% to 14.21%) in urban settings. 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 prevention strategies to reduce Strep A transmission.