Predictors of fatality in influenza A virus subtype infections among inpatients in the 2015-2016 season.

Background: Infection with the influenza A virus can cause severe disease and mortality. The effect of the different subtypes of influenza on morbidity and mortality is not yet known in Turkey. The aim of this study was to describe the predictors of fatality related to influenza A infection among hospitalized patients in Istanbul during the 2015-2016 influenza season, and to detail the differences between infections caused by H3N2 and H1N1.

Methods: This was a multicenter study performed by the Istanbul Respiratory Infections Study Group of The Turkish Society of Clinical Microbiology and Infectious Diseases (KLİMİK), among patients hospitalized for influenza in Istanbul during the 2015-2016 influenza season.

Results: A total of 222 patients hospitalized with laboratory-confirmed influenza during the 2015-2016 season were included in the study, of whom 25 (11.2%) died. The fatality rate was significantly higher among patients older than 65 years of age and those with chronic heart and kidney diseases (p<0.001), chronic neurological diseases (p=0.009), and malignancies (p=0.021). Thrombocyte counts were lower in those who died than in those who survived (p<0.004). The median alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, creatinine phosphokinase, and C-reactive protein levels were higher among fatal cases. In the multivariate analysis for the prediction of fatality, being >65years old (odds ratio (OR) 6.9, 95% confidence interval (CI) 2.07-23.08, p=0.002), being infected with influenza A(H3N2) (OR 4.2, 95% CI 1.27-14.38, p=0.019), and a 1-day delay in antiviral use (OR 1.28, 95% CI 1.01-1.63, p=0.036) were found to be associated with an increased likelihood of fatality.

Conclusions: The case fatality rate of influenza A(H3N2) was significantly higher than that of influenza A(H1N1). Detection of the infection, allowing the opportunity for the early use of antiviral agents, was found to be important for the prevention of fatality. The vaccination should be prioritized for at-risk groups.