Severity and outcomes of influenza-related pneumonia in type A and B strains in China, 2013-2019

Background Inconsistencies exist regarding the severity of illness caused by different influenza strains. The aim of this study was to compare the clinical outcomes of hospitalized adults and adolescents with influenza-related pneumonia (Flu-p) from type A and type B strains in China. Methods We retrospectively reviewed data from Flu-p patients in five hospitals in China from January 2013 to May 2019. Multivariate logistic and Cox regression models were used to assess the effects of influenza virus subtypes on clinical outcomes, and to explore the risk factors of 30-day mortality for Flu-p patients. Results In total, 963 laboratory-confirmed influenza A-related pneumonia (FluA-p) and 386 influenza B-related pneumonia (FluB-p) patients were included. Upon adjustment for confounders, multivariate logistic regression models showed that FluA-p was associated with an increased risk of invasive ventilation (adjusted odds ratio [aOR]: 3.824, 95% confidence interval [CI]: 2.279-6.414; P < 0.001), admittance to intensive care unit (aOR: 1.630, 95% CI: 1.074-2.473, P = 0.022) and 30-day mortality (aOR: 2.427, 95% CI: 1.568-3.756, P < 0.001) compared to FluB-p. Multivariate Cox regression models confirmed that influenza A virus infection (hazard ratio: 2.637, 95% CI: 1.134-6.131, P = 0.024) was an independent predictor for 30-day mortality in Flu-p patients. Conclusions The severity of illness and clinical outcomes of FluA-p patients are more severe than FluB-p. This highlights the importance of identifying the virus strain during the management of severe influenza.