Abstract
A novel pandemic influenza A(H1N1)pdm09 virus emerged in 2009 globally, and it continues to circulate in humans. The National Influenza Surveillance Network in Taiwan identified five A(H1N1)pdm09-predominant seasons, representing the 2009/2010, 2010/2011, 2012/2013, 2013/2014, and 2015/2016 outbreaks from 2009 to 2016. Independently, a retrospective cohort study (which enrolled 639 infected patients during the five seasons) was conducted at Chang Gung Memorial Hospital to explore the risk factors associated with influenza A(H1N1)pdm09-related complications. A phylogenetic analysis of hemagglutinin (HA) sequences showed that the circulating A(H1N1)pdm09 virus belonged to clades 1, 2, and 8 in 2009/2010; clades 3, 4, 5, and 7 in 2010/2011; clades 7 and 6C in 2012/2013; clades 6B in 2013/2014; and 6B/6B.1/6B.2 in 2015/2016. Compared to individuals infected in non-6B/6B.1/6B.2 seasons (2009/2010, 2010/2011, and 2012/2013), those infected in 6B/6B.1/6B.2 seasons (2013/2014 and 2015/2016) were at higher risk for influenza-related complications (adjusted odds ratio [aOR]: 1.6, 95% confidence interval [CI]: 1.0–2.8), pneumonia (aOR: 1.78, 95% CI: 1.04–3.04), mechanical ventilation (aOR: 2.6, 95% CI: 1.2–5.6), and acute respiratory distress syndrome (aOR: 5.5, 95% CI: 1.9–15.9). For the increased severity of infection during the influenza A(H1N1)pdm09 clade 6B/6B.1/6B.2 seasons, aspects related to the antigenic change of A(H1N1)pdm09 virus, immune response of the host, and environmental factors required further investigation.
Highlights
The 2013/2014 clade 6B-predominant season in the United States represented the first influenza A(H1N1) pdm[09] season since the emergence of the virus in 2009, and it was characterized by elevated rates of hospitalization among adults aged 50–64 years[3,4]
The long-term National Influenza Surveillance Network described the epidemiologic pattern of circulating viruses, and it has successfully identified the outbreaks of severe acute respiratory syndrome (SARS)-associated coronavirus and adenovirus[8,9]
The present study aimed to describe the A(H1N1)pdm[09] epidemiological and virological data obtained from the National Influenza Surveillance Network that reported laboratory-confirmed influenza cases in intensive care units during a 7-year period extending from the 2009/2010 season to the 2015/2016 season
Summary
The 2013/2014 clade 6B-predominant season in the United States represented the first influenza A(H1N1) pdm[09] season since the emergence of the virus in 2009, and it was characterized by elevated rates of hospitalization among adults aged 50–64 years[3,4]. The long-term National Influenza Surveillance Network described the epidemiologic pattern of circulating viruses, and it has successfully identified the outbreaks of severe acute respiratory syndrome (SARS)-associated coronavirus and adenovirus[8,9]. We conducted a retrospective cohort study at Chang-Gung Memorial Hospital to analyze the clinical characteristics and complications of patients with A(H1N1)pdm[09] virus infection in the five A(H1N1)pdm09-predominant seasons (2009/2010, 2010/2011, 2012/2013, 2013/2014, and 2014/2015) as identified by the National Influenza Surveillance Network. When these are considered, the results of these two approaches provided a better understanding of the impact of the new influenza A(H1N1)pdm[09] variant during predominant seasons on influenza A(H1N1)pdm[09] virus-associated complications
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