Epidemiology of Hospital Admissions with Influenza during the 2013/2014 Northern Hemisphere Influenza Season: Results from the Global Influenza Hospital Surveillance Network

PLoS One. 2016 May 19;11(5):e0154970. doi: 10.1371/journal.pone.0154970. eCollection 2016.


Background: The Global Influenza Hospital Surveillance Network was established in 2012 to obtain valid epidemiologic data on hospital admissions with influenza-like illness. Here we describe the epidemiology of admissions with influenza within the Northern Hemisphere sites during the 2013/2014 influenza season, identify risk factors for severe outcomes and complications, and assess the impact of different influenza viruses on clinically relevant outcomes in at-risk populations.

Methods: Eligible consecutive admissions were screened for inclusion at 19 hospitals in Russia, Turkey, China, and Spain using a prospective, active surveillance approach. Patients that fulfilled a common case definition were enrolled and epidemiological data were collected. Risk factors for hospitalization with laboratory-confirmed influenza were identified by multivariable logistic regression.

Findings: 5303 of 9507 consecutive admissions were included in the analysis. Of these, 1086 were influenza positive (534 A(H3N2), 362 A(H1N1), 130 B/Yamagata lineage, 3 B/Victoria lineage, 40 untyped A, and 18 untyped B). The risk of hospitalization with influenza (adjusted odds ratio [95% confidence interval]) was elevated for patients with cardiovascular disease (1.63 [1.33-2.02]), asthma (2.25 [1.67-3.03]), immunosuppression (2.25 [1.23-4.11]), renal disease (2.11 [1.48-3.01]), liver disease (1.94 [1.18-3.19], autoimmune disease (2.97 [1.58-5.59]), and pregnancy (3.84 [2.48-5.94]). Patients without comorbidities accounted for 60% of admissions with influenza. The need for intensive care or in-hospital death was not significantly different between patients with or without influenza. Influenza vaccination was associated with a lower risk of confirmed influenza (adjusted odds ratio = 0.61 [0.48-0.77]).

Conclusions: Influenza infection was detected among hospital admissions with and without known risk factors. Pregnancy and underlying comorbidity increased the risk of detecting influenza virus in patients hospitalized with influenza-like illness. Our results support influenza vaccination as a measure for reducing the risk of influenza-associated hospital admission.

Publication types

  • Multicenter Study

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Child
  • Child, Preschool
  • China
  • Cluster Analysis
  • Comorbidity
  • Epidemiological Monitoring
  • Female
  • Humans
  • Infant
  • Infant, Newborn
  • Influenza, Human / epidemiology*
  • Male
  • Middle Aged
  • Multivariate Analysis
  • Odds Ratio
  • Orthomyxoviridae
  • Outcome Assessment, Health Care
  • Patient Admission
  • Pregnancy
  • Pregnancy Complications, Infectious
  • Prospective Studies
  • Risk
  • Risk Factors
  • Russia
  • Spain
  • Turkey
  • Young Adult

Grants and funding

The study was funded by a collaboration between CSISP (now FISABIO) in Valencia, Spain; the D.I. Ivanovsky Institute of Virology in Moscow, Russian Federation; the Research Institute of Influenza in St. Petersburg, Russian Federation; the National Influenza Reference Laboratory Capa-Istanbul, Turkey; Division of Infectious Disease, Key Laboratory of Surveillance and Early-Warning on Infectious Disease, Chinese Center for Disease Control and Prevention, Beijing, China; School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China and Sanofi Pasteur. Sanofi Pasteur participated in the design of the study but did not participate in the collection, management, analysis, or interpretation of the data, writing the manuscript, or the decision to submit the manuscript for publication. Sanofi Pasteur provided support in the form of a salary for CES but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of this author are articulated in the 'author contributions' section.