Epidemiological and clinical characteristics of hospitalized influenza patients, Beijing, 2016–2018

ObjectiveTo understand the epidemiologic and clinical characteristics of laboratory-confirmed influenza A and B cases in hospitalized patients with severe acute respiratory infection (SARI), and explore the association between illness severity and influenza type.

MethodsDescriptive epidemiologic analysis was conducted on the data of laboratory-confirmed influenza cases detected through SARI sentinel surveillance in Beijing from August 2016 to July 2018. Influenza patients were regarded as severe cases if they needed invasive mechanical ventilation, or received ICU treatment, or died during hospitalization; or else they were regarded as mild cases. Multivariate logistic regression model was used to explore the association between type/subtype of influenza and illness severity.

ResultsAmong 746 hospitalized influenza patients, 42.4%(316/746) were cases ≥60 years old and 33.8%(252/746) were <5 years old. 598 were infected with influenza A virus (80.2%) and 148 were infected with influenza B virus (19.8%). Six patients needed invasive mechanical ventilation (0.8%, 6/746), 17 patients needed intensive care (2.9%, 17/746) and 4 patients died during hospitalization (0.5%, 4/746). Influenza A patients had 1.3 times hider risk to have severe clinical course compared with influenza B patients (OR＝1.3, 95% CI: 0.4–4.7, P＝0.655). Compared with patients with influenza B/Yamagata virus infection, patients infected with influenza A(H1N1) pdm09 virus had 2.1 times higher risk to have severe clinical course (OR＝2.1, 95% CI: 0.5–8.5, P＝0.295).

ConclusionThe hospitalized influenza patients were mostly the elderly and young children. Further studies are needed to confirm whether the clinical severity of influenza A is worse than that of influenza B.