Effect of a wet market on coronavirus disease (COVID-19) transmission dynamics in China, 2019–2020

•Employing statistical modeling analyses, we elucidated the effects of a ‘wet market’ on coronavirus disease (COVID-19) transmission dynamics in China, by stratifying cases with contact history with the Huanan Seafood Wholesale Market.•For market-to-human transmission, we estimated mean R at 0.24 (95% CrI: 0.01–1.38), with the reporting rate identified as being 2–34-fold higher compared with human-to-human transmission.•The proportion of asymptomatic/mild-symptom patients constitutes a substantial component of the COVID-19 disease burden. The novel coronavirus (SARS-CoV-2) originating from Wuhan spread rapidly throughout China. While its origin remains uncertain, accumulating evidence links a wet market with the early spread of SARS-CoV-2 in Wuhan. Similarly, the influence of the marketplace on the early transmission dynamics is yet to be investigated. Using the daily series of COVID-19 incidence, stratified according to contact history with the market, we have conducted quantitative modeling analyses to estimate the reproduction numbers (R) for market-to-human and human-to-human transmission, the reporting probability, and the early effects of public health interventions. We estimated R at 0.24 (95% CrI: 0.01–1.38) for market-to-human transmission and 2.37 (95% CrI: 2.08–2.71) for human-to-human transmission during the early spread in China (2019–2020). Moreover, we estimated that the reporting rate for cases stemming from market-to-human transmission was 2–34 fold higher than that for cases stemming from human-to-human transmission, suggesting that contact history with the wet market played a key role in identifying COVID-19 cases. Our R estimate tied to market-to-human transmission had substantial uncertainty, but it was significantly lower compared with the reproduction number driving human-to-human transmission. Our results also suggest that asymptomatic and subclinical infections constitute a substantial component of the COVID-19 morbidity burden.