Strongly heterogeneous transmission of COVID-19 in mainland China: local and regional variation

Yuke Wang; Peter F.M. Teunis

where t is the number of days after 20 February 2020. The parameters were estimated using the travel history records from the 228 confirmed cases in Beijing. The fitted logistic relation was then used to impute contacts with Wuhan sources for all cases outside Hubei province with unknown travel history. Once infection has been imported from Wuhan, further transmission depends on local contacts: all cases cannot be assumed to be fully connected. Local contacts were imputed by distributing cases within a province or city into clusters. Cases within a cluster were assumed fully connected while cases in different clusters were not connected, thus allowing only transmission within a cluster and not between clusters. Cluster size was assumed random, with average size five people, and a high probability (88·8%) of small clusters (average 1 to 5 people) and a low probability (11·2%) of medium to large clusters (average 10 to 25 people). The transmission probability matrix may be used to estimate reproduction numbers by calculating the row sums