title: High Body Mass Index as a Risk Factor for Hospitalization Due to Influenza: A Case-Control Study.
abstract: BACKGROUND
  Obesity has emerged as a significant independent predictor of severity in pandemic influenzaA (H1N1)pdm09. The aim of this study was to investigate the association between body mass index (BMI) and the risk of hospitalization due to influenza.
  
  
  METHODS
  Hospitalized patients (n=755) with laboratory-confirmed influenza were individually matched by age, admission/visit date, and province with an outpatient (n=783) with laboratory-confirmed influenza and an outpatient control (n=950). We compared the BMI using conditional logistic regression adjusted for potential confounding factors (aOR). The population attributable fraction (PAF) was calculated.
  
  
  RESULTS
  A higher BMI was associated with an increased risk of hospitalization compared to both outpatient cases (aOR=1.11; 95%CI: 1.07-1.16) and outpatient controls (aOR=1.04; 95%CI: 1.01-1.07). Compared with normal weight, obesity type I, obesity type II and obesity type III was associated with a greater likelihood of hospitalization compared with outpatient cases (aOR=1.85, 95%CI: 1.05-3.26; aOR=5.24, 95%CI: 1.94-14.15 and aOR=44.38, 95%CI: 4.47-440.5). Compared with normal weight, obesity type II and obesity type III was associated with a greater likelihood of hospitalization compared with outpatient controls (aOR=4.37, 95%CI: 1.79-10.69 and aOR=4.95, 95%CI: 1.45-16.87). In persons without influenza vaccination, all categories of BMI≥30kg/m(2) were associated with a greater likelihood of hospitalization compared with normal weight in both outpatient cases and outpatient controls. The PAF of hospitalization by influenza due to BMI ranged from 21.9% to 8.5%; in the case of unvaccinated against influenza between 20.5% to 16.9%.
  
  
  CONCLUSIONS
  A high BMI is associated with an increased risk of hospitalization due to influenza. High percentage of hospital admissions are attributable to their BMI, especially in non vaccinated.
authors.affiliation: Grupo de Investigación interacciones gen-ambiente y salud, Universidad de León, León, España; CIBER Epidemiología y Salud Pública, Madrid, España. Electronic address: vicente.martin@unileon.es.
authors.forename: Vicente
authors.initials: V
authors.lastname: Martín
authors.affiliation: CIBER Epidemiología y Salud Pública, Madrid, España; Instituto de Salud Pública de Navarra, Pamplona, España.
authors.forename: Jesús
authors.initials: J
authors.lastname: Castilla
authors.affiliation: CIBER Epidemiología y Salud Pública, Madrid, España; Departament de Salut, Generalitat de Catalunya, Barcelona, España.
authors.forename: Pere
authors.initials: P
authors.lastname: Godoy
authors.affiliation: CIBER Epidemiología y Salud Pública, Madrid, España; División de Medicina Preventiva y Salud Pública, Universidad de Jaén, Jaén, España.
authors.forename: Miguel
authors.initials: M
authors.lastname: Delgado-Rodríguez
authors.affiliation: CIBER Epidemiología y Salud Pública, Madrid, España.
authors.forename: Nuria
authors.initials: N
authors.lastname: Soldevila
authors.affiliation: Grupo de Investigación interacciones gen-ambiente y salud, Universidad de León, León, España.
authors.forename: Tania
authors.initials: T
authors.lastname: Fernández-Villa
authors.affiliation: Grupo de Investigación interacciones gen-ambiente y salud, Universidad de León, León, España.
authors.forename: Antonio J
authors.initials: AJ
authors.lastname: Molina
authors.affiliation: Subdirección de Vigilancia, Comunidad de Madrid, Madrid, España.
authors.forename: Jenaro
authors.initials: J
authors.lastname: Astray
authors.affiliation: CIBER Enfermedades Respiratorias, Madrid, España.
authors.forename: Ady
authors.initials: A
authors.lastname: Castro
authors.affiliation: CIBER Epidemiología y Salud Pública, Madrid, España; Unidad Mixta Genómica y Salud CSISP (FISABIO), Universitat de València, Valencia, España.
authors.forename: Fernando
authors.initials: F
authors.lastname: González-Candelas
authors.affiliation: Servicio de Vigilancia de Andalucía, Sevilla, España.
authors.forename: José María
authors.initials: JM
authors.lastname: Mayoral
authors.affiliation: CIBER Epidemiología y Salud Pública, Madrid, España; Fundación Vasca de Innovación e Investigación Sanitarias, Sondika, Vizcaya, España.
authors.forename: José María
authors.initials: JM
authors.lastname: Quintana
authors.affiliation: CIBER Epidemiología y Salud Pública, Madrid, España; Departament de Salut Pública, Universitat de Barcelona, Barcelona, España.
authors.forename: Ángela
authors.initials: Á
authors.lastname: Domínguez
mesh_terms: D000368:Aged; D000437:Alcoholism / Q000453:epidemiology; D015992:Body Mass Index; D016022:Case-Control Studies; D015897:Comorbidity; D004522:Educational Status; D005260:Female; D006760:Hospitalization; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000453:epidemiology* / Q000628:therapy; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology*; D058873:Pandemics; D011014:Pneumonia / Q000453:epidemiology; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology; D013030:Spain / Q000453:epidemiology; D014611:Vaccination / Q000706:statistics & numerical data
chemical_list: D007252:Influenza Vaccines
keywords: Body mass index; Case control study; Estudio de casos y controles; Fracción atribuible poblacional; Gripe; Hospitalization risk; Influenza; Obesidad; Obesity; Population attributable fraction; Riesgo de hospitalización; Índice de masa corporal