Application of moving epidemic method in establishing epidemic and intensity thresholds of influenza in winter and summer seasons in Guangzhou, Guangdong

Objective To establish the monitoring threshold of influenza in Guangzhou, Guangdong province, evaluate the incidence intensity of influenza, and provide scientific basis for the prevention and control of influenza at different levels.

Methods The weekly number of reported influenza cases in Guangzhou from 2014 to2022 were obtained from National Disease Prevention and Control Information System. By using moving epidemic method (MEM), the incidence peaks in winter and summer were used in the study. The δ value of the maximum Youden’s index was selected as the optimal δ parameter. MEM was applied to calculate the influenza epidemic and intensity thresholds and its effectiveness was evaluated by cross-validation method. The epidemic level of influenza from 2014 to 2022 was also evaluated.

Results  For winter, the pre-epidemic threshold and post-epidemic threshold were 1178 cases and 1103 cases, and the medium, high and very high intensity thresholds were 3653 cases, 10722 cases and 18959 cases. For summer, the pre-epidemic threshold and post-epidemic threshold were 652 cases and 267 cases, and the medium, high and very high intensity thresholds were 1400 cases, 3076 cases and 4666 cases. Sensitivity and specificity of two models for summer and winter were ≥0.90. The incidence intensity reached very high level in winter in 2019 and summer in 2022, medium level in summer in 2015, summer in 2016 and winter in 2017, low level in summer in 2014, but remained baseline level all the year round in 2021.

Conclusion MEM model used to establish the epidemic and intensity threshold of influenza in summer and winter in Guangzhou has good sensitivity and specificity. It can provide scientific evidence for the surveillance for incidence level of influenza and the prevention and control of influenza.