Epidemiological characteristics of influenza and characteristics of hemagglutinin gene of B-Victoria strains in Hebei Province from 2018 to 2019

Abstract

Objective: To understand the epidemiological characteristics of influenza in Hebei Province from 2018 to 2019, and to analyze the characteristics and variation of hemagglutinin(HA) gene of influenza B-Victoria(BV) strains. Methods: Throat swab specimens of influenza-like cases within 3 days of fever were collected from 28 sentinel hospitals in Hebei province, meanwhile, The surveillance data was collected by the Chinese National Influenza Surveillance Network from April 2018 to March 2019, Throat swab specimens were collected from patients with influenza-like symptoms in sentinel hospitals, and tested by RT-PCR and virus isolation. 14 influenza B-Victoria strains from different regions were selected to sequence HA gene, Phylogenetic tree and the molecular characteristics were analyzed by DNASTAR 7.0 and Mega-X software. Results: From 2018 to 2019, A total of 99 266 cases of influenza-like illness (ILI) were detected from 4 689 103 cases by 28 influenza sentinel hospitals in Hebei Province, the visit percentage of ILI was 2.12%. During the period, 18 730 samples were detected, and 2 752(14.69%) samples were positive tested by RT-PCR, the peak was in the third week of 2019(44.92%), In the early stage of epidemic season, Influenza A(H1N1)pdm09 virus was the main type, while BV virus was the main type in the late stage. HA gene sequence analysis showed that the 14 BV viruses belonged to 162-164 amino acid deletion strains, the amino acid homology between HA sequences was 97.16%-100.00%, and 97.16%-98.95% compared with the vaccine strain B/Colorado/06/2017 recommended by WHO. Compared with the vaccine strains, 14 strains involved 11 amino acid site mutations. Conclusion: Influenza was prevalent in winter and spring in Hebei province from 2018 to 2019, Multiple mutations in antigenic sites of BV viruses might be related to the outbreaks.