Abstract
BackgroundInconsistencies 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.MethodsWe 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.ResultsIn 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.ConclusionsThe 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.
Highlights
Inconsistencies exist regarding the severity of illness caused by different influenza strains
Exclusion criteria were as follows: (i) Aged ≤ 14 years; (ii) not classified as community-onset pneumonia, as it was difficult to determine whether nosocomial pneumonia occurred after the onset the influenza; (iii) it has been reported that the clinical characteristics and outcomes of immunocompromised patients with influenza differ to those of immunocompetent hosts
Multivariate Cox regression models confirmed that influenza A virus infection, age (HR: 1.055, 95% Interval confidence (CI): 1.033–1.077, P < 0.001), cardiovascular disease (HR: 7.683, 95% CI: 3.175–18.58, P < 0.001), smoking history (HR: 3.137, 95% CI: 1.417–7.124, P < 0.001), lymphocytes < 0.8 × 109/L (HR: 10.473, 95% CI: 5.033–21.792, P < 0.001), blood urea nitrogen (BUN) > 7 mmol/L (HR: 3.170, 95% CI: 1.449–6.935, P = 0.004) and arterial Hydrogen ion index (pH) < 7.35 (HR: 3.037, 95% CI: 1.552–5.945, P = 0.001) were independent risk factors for 30-day mortality in Influenza-related pneumonia (Flu-p) patients (Table 4)
Summary
Inconsistencies exist regarding the severity of illness caused by different influenza strains. It is estimated that each year, 1 billion cases of symptomatic influenza infection have occurred across the globe, including 3–5 million cases of severe illness and 290 000–650 000 cases of influenzarelated respiratory deaths [3]. Kilbourne suggested that the disease features caused by different influenza virus subtypes are clinically indistinguishable [8]. Several studies have examined the hypothesis that the severity of illness caused by influenza is associated with causal virus types. To understand the differences of the severity and outcomes between specific influenza virus types is of great significance to arrange rational diagnositic testings, carry out prompt antiviral treatment and make other clinical decisions in the management of severe influenza
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