BACKGROUND: Since 2011, the Global Influenza Hospital Surveillance Network (GIHSN) has used active surveillance to prospectively collect epidemiological and virological data on patients hospitalized with influenza virus infection. Here, we describe influenza virus strain circulation in the GIHSN participant countries during 2017-2018 season and examine factors associated with complicated hospitalization among patients admitted with laboratory-confirmed influenza illness. METHODS: The study enrolled patients who were hospitalized in a GIHSN hospital in the previous 48 h with acute respiratory symptoms and who had symptoms consistent with influenza within the 7 days before admission. Enrolled patients were tested by reverse transcription-polymerase chain reaction to confirm influenza virus infection. "Complicated hospitalization" was defined as a need for mechanical ventilation, admission to an intensive care unit, or in-hospital death. In each of four age strata (< 15, 15-< 50, 50-< 65, and ≥ 65 years), factors associated with complicated hospitalization in influenza-positive patients were identified by mixed effects logistic regression and those associated with length of hospital stay using a linear mixed-effects regression model. RESULTS: The study included 12,803 hospitalized patients at 14 coordinating sites in 13 countries, of which 4306 (34%) tested positive for influenza. Influenza viruses B/Yamagata, A/H3N2, and A/H1N1pdm09 strains dominated and cocirculated, although the dominant strains varied between sites. Complicated hospitalization occurred in 10.6% of influenza-positive patients. Factors associated with complicated hospitalization in influenza-positive patients included chronic obstructive pulmonary disease (15-< 50 years and ≥ 65 years), diabetes (15-< 50 years), male sex (50-< 65 years), hospitalization during the last 12 months (50-< 65 years), and current smoking (≥65 years). Chronic obstructive pulmonary disease (50-< 65 years), other chronic conditions (15-< 50 years), influenza A (50-< 65 years), and hospitalization during the last 12 months (< 15 years) were associated with a longer hospital stay. The proportion of patients with complicated influenza did not differ between influenza A and B. CONCLUSIONS: Complicated hospitalizations occurred in over 10% of patients hospitalized with influenza virus infection. Factors commonly associated with complicated or longer hospitalization differed by age group but commonly included chronic obstructive pulmonary disease, diabetes, and hospitalization during the last 12 months.

Canadian Center for Vaccinology IWK Health Centre and Nova Scotia Health Authority Dalhousie University Halifax Canada

Center for Vaccine Development and Global Health University of Maryland School of Medicine Baltimore MD USA

CIRI Lyon University Inserm U 1111 Lyon France

Claude Bernard University Lyon France

Department of Science and Technology National Research Foundation Vaccine Preventable Diseases Unit University of the Witwatersrand Johannesburg South Africa

Division of Infectious Diseases Chinese Center for Disease Control and Prevention Beijing China

Emerging Pathogens Laboratory Epidemiology and International Health Fondation Mérieux Centre International de Recherche en Infectiologie Lyon France

FSBI N F Gamaleya NRCEM Moscow Russian Federation

Groupement Hospitalier Edouard Herriot Unité d'Hygiène Epidémiologie et Prévention Hospices Civils de Lyon Lyon France

Hospices Civils de Lyon Croix Rousse University Hospital Infectious Agents Institute Lyon France

Inserm F CRIN Innovative Clinical Research Network in Vaccinology CIC 1417 Paris France

Institute of Health Metrics and Evaluation Department of Health Metrics Sciences University of Washington Seattle WA USA

Medical Research Council Respiratory and Meningeal Pathogens Research Unit School of Pathology Faculty of Health Sciences University of the Witwatersrand Johannesburg South Africa

National Institute of Public Health Prague Czech Republic

National Institutes of Health Mexico City Mexico

Netherlands Institute for Health Services Research Utrecht The Netherlands

OpenHealth Paris France

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The Global Influenza Hospital Surveillance Network: A Multicountry Public Health Collaboration

Predictors of Severity of Influenza-Related Hospitalizations: Results From the Global Influenza Hospital Surveillance Network (GIHSN)