Age differences in comorbidities, presenting symptoms and outcomes of influenza illness requiring hospitalization: a worldwide perspective from the Global Influenza Hospital Surveillance Network

Background The Global Influenza Hospital Surveillance Network (GIHSN) was established in 2012 to conduct coordinated worldwide influenza surveillance. Here we describe underlying comorbidities, symptoms, and outcomes in hospitalized patients with influenza. Methods Between November/2018 and October/2019, GIHSN included 19 sites in 18 countries using a standardized surveillance protocol. Influenza infection was laboratory-confirmed with RT-PCR. A multivariate logistic regression model was utilized to analyze the extent to which various risk factors predict severe outcomes. Results Of 16,022 enrolled patients, 21,9% had laboratory-confirmed influenza; 49.2% of influenza cases were A/H1N1pdm09. Fever and cough were the most common symptoms, though they decreased with age (p Conclusions Both virus and host factors contributed to influenza burden. We identified age differences in comorbidities, presenting symptoms, and adverse clinical outcomes among those hospitalized with influenza, and benefit from influenza vaccination in protecting against adverse clinical outcomes. The GIHSN provides an ongoing platform for global understanding of hospitalized influenza illness.