Factors associated with hospitalization for seasonal influenza in a Japanese nonelderly cohort

Abstract

Background: Nonelderly patients may require hospitalization if their symptoms of influenza are severe. However, little evidence is available about the risk factors for hospitalization for influenza. Methods: We used a multicenter outpatient and inpatient database to obtain patients' characteristics and clinical procedures. We identified patients aged <65 years with a confirmed diagnosis of influenza between October 2013 and December 2014. We used a Cox regression model to identify the risk factors for hospitalization, using a comparison group of individuals with a confirmed diagnosis of influenza but who were not hospitalized. Results: Of 88,054 patients diagnosed with influenza, 276 (0.3 %) patients were hospitalized. With reference to patients aged 18-64 years, the hazard ratio (95 % confidence interval) for hospitalization in patients aged <2, 2-4, and 5-17 years was 12.25 (8.37-17.93), 4.56 (3.10-6.72) and 1.45 (1.03-2.05), respectively. Anemia, chronic obstructive pulmonary disease, neurologic disease, and regular steroid use were significantly associated with hospitalization. Hazard ratios were adjusted for age, sex, comorbidities, respiratory co-infection, virus type, and influenza season. Conclusions: Our findings suggest that younger age and several comorbidities are associated with higher probability of hospitalization for influenza.