ObjectiveUsing a spatio-temporal clustering analysis of varicella in Shanghai from 2006 to 2015 at a subdistrict level， we aim to provide decision support for formulating a reasonable varicella prevention strategy.

MethodsBased on the data of varicella cases in Shanghai from 2006 to 2015， SaTScan was employed to detect and analyze the spatial pattern of varicella clusters. Moreover， field investigation was combined to infer and explain the risk factors of varicella clusters.

ResultsThe spread of varicella in Shanghai from 2006 to 2015 had an obvious annual change and spatial differentiation at a subdistrict level. The findings of SaTScan showed that with a confidence level of 99.9%， there were totally 7 spatio-temporal clustering events in Shanghai from 2006 to 2015， in which 3 events were regional events and 4 were independent events. Independent events usually lasted for 2-4 years， while regional events in the "Jiading-Chongming district" and "Songjiang-Minhang district" areas had a longer duration and a larger impact.

ConclusionsFrom 2006 to 2015， there is an obvious temporal and spatial clustering pattern of varicella in Shanghai. Majority of abnormal spatio-temporal clusters occur in rural areas rather than urban areas， which may be related to increasing floating population and migration of susceptible population caused by the implementation of large-scale construction projects.