Objectives: The moving epidemic method (MEM) has been implemented well for assessing seasonal influenza epidemics in temperate regions. We used the MEM to establish epidemic threshold for influenza in Guangdong, a subtropical province in China.

Methods: Influenza virology surveillance data from 2011/2012 to 2017/2018 seasons in Guangdong were applied in MEM to calculate the epidemic threshold and timeliness of the detection of epidemic for 2018/2019 influenza season. Weekly positive proportion of influenza A(H1N1)pdm09, A(H3N2), B/Victoria-lineage and B/Yamagata-lineage were separately adapted to calculate the subtype-specific epidemic threshold. The performance of MEM was evaluated using a cross-validation procedure.

Results: For 2018/2019 influenza season, the epidemic threshold of weekly positive proportion was 15.08%. The timeliness of epidemic detection for 2018/2019 season was 1 week. Influenza A(H1N1)pdm09, B/Yamagata-lineage and B/Victoria-lineage prevailed during winter and spring and their epidemic threshold was 5.12%, 4.53% and 4.38% respectively. Influenza A(H3N2) was active in the summer with an epidemic threshold of 11.99%.

Conclusions: The MEM using influenza virology surveillance data stratified by types of influenza virus was implemented effectively in Guangdong, China. This study provided a practical manner for subtropical regions to establish local influenza epidemic threshold.