title: Factors associated with hospitalization for seasonal influenza in a Japanese nonelderly cohort.
abstract: 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.
  
  
  
  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.
  
  
  
  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.
  
  
  
  Our findings suggest that younger age and several comorbidities are associated with higher probability of hospitalization for influenza.
authors: Department of Clinical Epidemiology and Health Economics, School of Public Health, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 1130033, Japan. sachikoono-tky@umin.ac.jp.
authors: Sachiko
authors: S
authors: Ono
authors: Department of General Medicine, National Defense Medical College, 3-2 Namiki, Tokorozawa, Saitama, 3598513, Japan.
authors: Yosuke
authors: Y
authors: Ono
authors: Department of Clinical Epidemiology and Health Economics, School of Public Health, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 1130033, Japan.
authors: Hiroki
authors: H
authors: Matsui
authors: Department of Clinical Epidemiology and Health Economics, School of Public Health, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 1130033, Japan.
authors: Hideo
authors: H
authors: Yasunaga
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D015897:Comorbidity; D016208:Databases, Factual; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007251:Influenza, Human / Q000453:epidemiology* / Q000209:etiology; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D012307:Risk Factors; D012621:Seasons; D012720:Severity of Illness Index; D055815:Young Adult
keywords: Hospitalization; Nonelderly patient; Risk factor; Seasonal influenza