title: Smoking may increase the risk of hospitalization due to influenza.
abstract: Smoking may facilitate influenza virus infections and their severity. The objective was to investigate the risk of hospitalization due to influenza in Spanish smokers and ex-smokers.
  
  
  
  We carried out a multicentre, case-control study in 2011. Cases [patients ≥ 18 years hospitalized > 24 h with real time polymerase chain reaction (RT-PCR)-confirmed influenza] were selected from 29 Spanish hospitals. For each case, we selected an outpatient aged ≥ 18 years with RT-PCR-confirmed influenza matched by age (±5 years), date of hospitalization of the case (±10 days) and province of residence. We collected epidemiological variables, comorbidities and the smoking history. The risk of hospitalization due to smoking was determined by the adjusted odds ratio (aOR) using logistic regression.
  
  
  
  We studied 471 hospitalized cases and 476 outpatient cases. Hospitalized cases had a higher frequency of influenza risk factors compared with outpatient cases. Hospitalized cases had a higher frequency of smoking (30.9% vs. 17.1%) and being ex-smokers (29.3% vs. 25.3%). Current smoking (aOR = 2.18, 95% CI: 1.23-3.87) and being an ex-smoker (aOR = 1.73, 95% CI: 1.07-2.82) were associated with the risk of hospitalization.
  
  
  
  Smoking may increase the risk of hospitalization in smokers and ex-smokers when infected by the influenza virus. Smoking prevention could reduce hospitalizations. Influenza vaccination is recommended for smokers.
authors.affiliation: Department of Health, Generalitat of Catalonia, Lleida, Spain pere.godoy@gencat.cat.|CIBER Epidemiology and Public Health, Madrid, Spain.|IRBLleida. University of Lleida, Lleida, Spain.
authors.forename: Pere
authors.initials: P
authors.lastname: Godoy
authors.affiliation: CIBER Epidemiology and Public Health, Madrid, Spain.|Public Health Institute, Navarra Institute for Health Research (IdiSNA), Pamplona, Spain.
authors.forename: Jesús
authors.initials: J
authors.lastname: Castilla
authors.affiliation: Epidemiological Surveillance Service. Andalusian Government, Sevilla, Spain.
authors.forename: José María
authors.initials: JM
authors.lastname: Mayoral
authors.affiliation: CIBER Epidemiology and Public Health, Madrid, Spain.|University of Jaen, Jaén, Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: Delgado-Rodríguez
authors.affiliation: CIBER Epidemiology and Public Health, Madrid, Spain.|Grupo de Investigación en Interacciones gen-ambiente-salud. Universidad de León, León, Spain.
authors.forename: Vicente
authors.initials: V
authors.lastname: Martín
authors.affiliation: Area of Epidemiology, Community of Madrid, Spain.
authors.forename: Jenaro
authors.initials: J
authors.lastname: Astray
authors.affiliation: CIBER Epidemiology and Public Health, Madrid, Spain.
authors.forename: Núria
authors.initials: N
authors.lastname: Soldevila
authors.affiliation: CIBER Epidemiology and Public Health, Madrid, Spain.|FISABIO-CSISP, University of Valencia, Valencia, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: González-Candelas
authors.affiliation: CIBER Respiratory Diseases, Madrid, Spain.
authors.forename: Ady
authors.initials: A
authors.lastname: Castro
authors.affiliation: CIBER Epidemiology and Public Health, Madrid, Spain.
authors.forename: Maretva
authors.initials: M
authors.lastname: Baricot
authors.affiliation: Ministry of Health, Government of Castile and Leon, Valladolid, Spain.
authors.forename: Sonia
authors.initials: S
authors.lastname: Tamames
authors.affiliation: CIBER Epidemiology and Public Health, Madrid, Spain.|IMIM - Hospital del Mar Medical Research Institute, Barcelona, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Alonso
authors.affiliation: CIBER Epidemiology and Public Health, Madrid, Spain.|University Hospital Ramón y Cajal, Madrid, Spain.
authors.forename: Juan C
authors.initials: JC
authors.lastname: Galán
authors.affiliation: CIBER Epidemiology and Public Health, Madrid, Spain.|Research Unit, Galdakao-Usansolo hospital, San Sebastian, Spain.
authors.forename: José María
authors.initials: JM
authors.lastname: Quintana
authors.affiliation: Spanish Network for Research in Infectious Diseases, Madrid, Spain.
authors.forename: Tomás
authors.initials: T
authors.lastname: Pumarola
authors.affiliation: CIBER Epidemiology and Public Health, Madrid, Spain.|Department of Public Health. University of Barcelona, Barcelona, Spain.
authors.forename: Angela
authors.initials: A
authors.lastname: Domínguez
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology / Q000209:etiology* / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D015995:Prevalence; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D013030:Spain / Q000453:epidemiology; D055815:Young Adult