title: Caesarean section and hospitalization for respiratory syncytial virus infection: a population-based study.
abstract: OBJECTIVE
  Hospitalization for respiratory syncytial virus (RSV) infection and asthma share common determinants, and meta-analyses indicate that children delivered by caesarean section (CS) are at increased risk of asthma. We aimed to investigate whether birth by CS is associated with an increased risk of hospitalization for RSV illness.
  
  
  METHODS
  This was a population-based national register-based cohort study, conducted between January, 1997 and June, 2003, which included all children born in Denmark and all hospitalizations for RSV disease in them from 0 to 23 months of age. We used Cox regression with adjustment for prematurity, asphyxia, birthweight, multiple births, single parenthood, maternal smoking during pregnancy, older siblings and asthma diagnoses up to 2 weeks before hospitalization for RSV infection, to compare the effects of acute or elective CS versus vaginal delivery, on subsequent hospitalization for RSV disease. A test for homogeneity was used to assess for effect over time.
  
  
  RESULTS
  399,175 children with 10,758 hospitalizations for RSV illness were included; 31,715 were born by acute CS and 30,965 by elective CS. Adjusted hazard ratios for hospitalization for RSV infection in children born by acute CS and by elective CS were 1.09 (1.01-1.17) and 1.27 (1.19-1.36), respectively. The effect of elective CS remained unchanged throughout the first 2 years of life (P = 0.53), whereas the effect of acute CS was only present in the second year of life (P = 0.001).
  
  
  CONCLUSIONS
  Delivery by caesarian section is associated with an increased risk of hospitalization for RSV infection. This effect continues at least throughout the first 2 years of life.
authors.affiliation: From the *Pediatric Department, University Hospital Naestved; †Pediatric Department, University Hospital Hillerød, Hillerød; ‡Pediatric Department, H.C. Andersen Children's Hospital, University Hospital Odense, Odense; §Department for Research in Women and Children, University Hospital Rigshospitalet, Copenhagen Ø; ¶Coraxo Consulting, Virum, Denmark; ‖Department of Pediatrics, Section of Infectious Diseases, University of Colorado Denver, School of Medicine; **Center for Global Health and Department of Epidemiology, Colorado School of Public Health and Children's Hospital Colorado, Aurora, CO; and ††Pediatric Department, University Hospital Rigshospitalet, 2100 København Ø, Denmark.
authors.forename: Kim
authors.initials: K
authors.lastname: Kristensen
authors.forename: Niels
authors.initials: N
authors.lastname: Fisker
authors.forename: Ann
authors.initials: A
authors.lastname: Haerskjold
authors.forename: Henrik
authors.initials: H
authors.lastname: Ravn
authors.forename: Eric A F
authors.initials: EA
authors.lastname: Simões
authors.forename: Lone
authors.initials: L
authors.lastname: Stensballe
mesh_terms: D001249:Asthma / Q000453:epidemiology* / Q000473:pathology*; D002585:Cesarean Section; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006760:Hospitalization; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011247:Pregnancy; D018357:Respiratory Syncytial Virus Infections / Q000453:epidemiology* / Q000473:pathology*; D018570:Risk Assessment