The Food-Trade Associated Spreading of COVID-19 Outbreak from a Contaminated Super Wholesale Food Market in Beijing

Abstract

Background: The re-emerging outbreak of COVID-19 in Beijing China in summer of 2020 was originated from a contaminated super food wholesale market. The transmission mechanism was analyzed. Methods: We hypothesized that the Xinfadi outbreak was associated with activities of food-trade. Therefore, all the confirmed cases were divided into groups of sellers, buyer, seller transmitted and buyer transmitted. Data for each case were georeferenced and aggregated to the 500m-spaced hexagon grids using geodata and base maps, road networks, urban points of interest from OpenStreetMap. The Xinfadi-related trade activity data were derived using Python crawling scripts. The spatial association of the outbreak was studied with Moran’s I statistic method and a Susceptible-Infected-Recovered (SIR) coupled Agent-Based Model (ABM). Findings: Of 335 cases reported, 177 (45·3%) were sellers who worked for the Market, 83 (23·7%) were buyers who visited the Market, and 74 were transmitted by either of the infected buyers or sellers. The Market was the outbreak center, which were spreading along the urban rapid transit lines. The areas with a high incidence were concentrated across neighborhoods in the southwest of Beijing's Fifth Ring Road and the west section of the Fourth Ring of southwestern Beijing, and the west portion of Fuxing Road. The highest number of seller transmission hubs were located in Market neighborhood, however the buyer transmission hubs extended to cover more than three different districts. Our SIR-ABM model analysis suggested that the trade-distancing strategy effectively reduced the R0. The retail shops closure strategy reduced nearly half number of visitors to market. The Buy-local policy option reduced more than 70% infection in total. Interpretation: The Xinfadi outbreak was associated contaminated super food market by people's movements for food-trade, including their interactions in related activities. Therefore, the retails closures and buy-local policy could reduce size of the outbreak and prevent possible outbreak in future.Funding Statement: Ministry of Science and Technology China (Grant number 2018ZX10712001-017 and 2018ZX10712001-018), Chinese Academy of Medical Sciences (2018RU010), Chinese Academy (2020-XZ-37) and the National Natural Science Foundation of China (71603253 and 72074209).Declaration of Interests: All authors declare no competing interests.