title: Population-based Analysis of Bronchiolitis Epidemiology in Valencia, Spain.
abstract: BACKGROUND
  There is a lack of European epidemiologic population-based studies on bronchiolitis and respiratory syncytial virus (RSV) bronchiolitis including both hospitalizations and primary care attendance.
  
  
  METHODS
  A retrospective cohort of all children born between 2009 and 2012 was followed from birth to 2 years of age using population and health databases. We searched for global bronchiolitis (International Classification of Diseases, 9th revision, Clinical Modification codes 466.1, 466.11 and 466.19) and RSV bronchiolitis (code 466.11 and code 466.19 with positive RSV test) in the first appearance either in primary care or in hospitalization databases. A preterm subcohort (International Classification of Diseases, 9th revision, Clinical Modification codes 765) was also analyzed.
  
  
  RESULTS
  The cohort consisted of 198,223 children of whom 41,479 were diagnosed of bronchiolitis (incidence rate 16.4/100 children <2 years per year). Of those, 5390 were hospitalized with the majority of hospitalizations occurring at <6 months of age (incidence rate of 5.2/100 children <6 months per year) and 3106 of the hospitalizations were RSV positive (incidence rate 3.2/100 children <6 months per year). RSV hospitalizations were 26% longer than non-RSV. In preterm infants, hospitalization incidence was more than double, and the mean length of hospitalization was 29% longer.
  
  
  CONCLUSIONS
  Most (87%) bronchiolitis cases are managed in primary care offices. Approximately 2 out of every 10 children <2 are diagnosed of bronchiolitis, 3 out of every 100 are hospitalized and 1.6 out of every 100 are hospitalized with RSV bronchiolitis in our cohort. Infants between 2 and 10 weeks constitute a risk group for severe bronchiolitis.
authors.affiliation: From the *Vaccine Research, Fundación para el Fomento de la Investigación Sanitaria y Biomédica de la Comunitat Valenciana, FISABIO-Public Health; and †Centro de Salud La Eliana, Valencia, Spain.
authors.forename: Cintia
authors.initials: C
authors.lastname: Muñoz-Quiles
authors.forename: Mónica
authors.initials: M
authors.lastname: López-Lacort
authors.forename: Isabel
authors.initials: I
authors.lastname: Úbeda-Sansano
authors.forename: Sara
authors.initials: S
authors.lastname: Alemán-Sánchez
authors.forename: Silvia
authors.initials: S
authors.lastname: Pérez-Vilar
authors.forename: Joan
authors.initials: J
authors.lastname: Puig-Barberà
authors.forename: Javier
authors.initials: J
authors.lastname: Díez-Domingo
mesh_terms: D001988:Bronchiolitis / Q000175:diagnosis / Q000453:epidemiology* / Q000209:etiology / Q000401:mortality; D015331:Cohort Studies; D005260:Female; D006760:Hospitalization; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011159:Population Surveillance; D012189:Retrospective Studies; D012959:Socioeconomic Factors; D013030:Spain / Q000453:epidemiology