Epidemiological and Phylogenetic Characteristics of Influenza B Infection in Severe Acute Respiratory Infection Cases in Beijing, 2014 to 2015

Abstract

Influenza B viral infection is of great importance, but the epidemiological and phylogenetic characteristics of influenza B infection in severe acute respiratory infection (SARI) cases are still unclear.The clinical information of 2816 SARI cases and 467,737 influenza-like illness (ILI) cases in Beijing area from September 2014 to April 2015 were collected and analyzed. Among them, 91 influenza B viruses isolated from SARI cases were sequenced.The overall yield rate of influenza A/B infection was 14.21% and 27.77% in sampled SARI and ILI cases, respectively. Compared with influenza A infection, the frequency of influenza B infection in SARI cases was higher in younger patients. Phylogenetic analysis suggested that most tested hemagglutination genes belonged to Yamagata lineage Clade 3, which were similar with current circulating viruses but different with 2014 to 2015 influenza season vaccine strain (Clade 2). Importantly, HA-Y3/NA-V4 intralineage reassorting was identified in Beijing area for the first time, which can act as a possible risk factor of SARIs.The influenza activity and virus types/subtypes/lineages among SARI patients were well correlated with that of ILI cases. Furthermore, the potential risk of reassorted influenza B virus infection should not be overlooked.

FIGURE 1

Map of Severe Acute Respiratory Infection sentinel sites in Beijing area. The sentinel hospitals are marked as red dots, and the districts which had at least one sentinel hospitals are in grey.

FIGURE 2

The influenza virus activity in SARI and ILI cases in Beijing areas from September 2014 to April 2015. The data were collected from sentinel hospitals and summarized every week. A, The LCI yield rate in SARI and ILI cases from September 2014 to April 2015. B, Week number of LCI by A/H1N1 (09 dpm) subtype, A/H3N2 subtype, B/Victoria, and B/Yamagata lineages in SARI cases. C, Week number of LCI by A/H1N1 (09 dpm) subtype, A/H3N2 subtype, B/Victoria, and B/Yamagata lineages in ILI cases. SARI = severe acute respiratory infection, ILI = Influenza-like illness, LCI = laboratory-confirmed influenza.

FIGURE 3

Phylogentic analysis of HA gene of influenza B-Yamagata lineage virus from severe acute respiratory infection and influenza-like illness cases. The phylogenetic trees were constructed using BEAST program and employing the general-time reversal HKY substitution model/strict clock model with a gamma-distributed rate parameter. The viruses isolated from severe acute respiratory infection cases were shown in red, and the vaccine strains were shown in blue. HA-Y3/NA-V4 reassortants were marked in yellow.

FIGURE 4

Phylogentic analysis of NA gene of influenza B-Yamagata lineage virus from severe acute respiratory infection and influenza-like illness cases. The phylogenetic trees were constructed using BEAST program and employing the general-time reversal HKY substitution model/strict clock model with a gamma-distributed rate parameter. The viruses isolated from severe acute respiratory infection cases were shown in red, and the vaccine strains were shown in blue. HA-Y3/NA-V4 reassortants were marked in yellow.