Abstract
Influenza-like illness (ILI) is one of the most important public health problems globally, causing an enormous disease burden. Influenza infections are the most common cause of ILI. Bacterial and virus co-infection is common yet the data of co-infection with influenza A and B viruses are scarce. To identify the epidemiological patterns of and co-infection of influenza A and B in Anhui province, China, we analyzed the surveillance data of 5 years from 2009 to 2014 collected by the Chinese National influenzas network. The results showed that the weekly ratio of ILI was 3.96 ± 1.9% (95% CI 3.73–4.2%) in outpatients and the highest affected population was children under 5 years old. The epidemic of influenza viruses was highest during 2009–2010. For the other 4 surveillance years, school-aged people (5–14 years) were the most highly affected population. Influenza B and H3N2 viruses were more prevalent than H1N1pdm09 virus after 2010. In addition, a significant co-circulation of influenza A (H1N1pdm09 and H3N2) and influenza B virus was detected with 0.057% PCR positive rate during 2009–2014 in Eastern China, yet isolated only in pediatric patients. Our data reveals school-aged population would be the main vulnerable population and a distinct seasonality for influenza. In addition, the co-infection of influenza A and B were found in Anhui Province, China. Ongoing surveillance is critical to understand the seasonality variation and make evidence-based vaccination recommendations. Information on the epidemiological patterns and co-infections of influenza A and B can help us to implement different strategies for selecting vaccine formulations and monitoring new emerging influenza strains. In addition, the identification of the susceptible population can help us to develop more precise protection measures.
Highlights
Influenza virus, one of the most important respiratory viruses presenting globally annual seasonal epidemics, causes fatal respiratory diseases to humans
Referring physicians at sentinel hospitals were asked to diagnose Influenza-like illness (ILI) according to strict criteria and to record the number of Abbreviations: ILI, influenza-like illness; Haemagglutination Inhibition Assay (HI), haemagglutination inhibition assay; HA, hemagglutinin
The results showed that weekly ILI ratio of outpatients was 3.96 ± 1.9% for the 5 surveillance years and were the highest in surveillance year of 2009–2010 (6.75 ± 3.05%, 95%CI: 5.72–7.43%)
Summary
One of the most important respiratory viruses presenting globally annual seasonal epidemics, causes fatal respiratory diseases to humans. The mortality related to influenza virus infections adhere to a cyclic pattern fluctuating with seasonal changes in temperature and humidity, or occasional pathogenicity changes due to new gene mutations or exchanges (2–5). The epidemiological and virological study of dual influenza infection cases is of major interest for monitoring emerging influenza strains, which could perpetuate epidemic or pandemic events. Co-infections with influenza A subtypes or/and influenza B virus were detected in several surveillance areas regarded as rare events (11). We described the epidemiological pattern of influenza A and B by surveillance network in Anhui province, eastern China from 2009 to 2014. We investigated co-infection of influenza A and B and identified the ssusceptible population
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