title: Changes in atopy prevalence and sibship effect in rural population at all ages.
abstract: BACKGROUND
  We examined the associations of family size and birth order with atopy prevalence in rural Poland at two time periods.
  
  
  METHODS
  Two cross-sectional surveys were conducted in the same villages and a small town of lower Silesia at an interval of 9 years. In 2003, 1700 (88% of eligible individuals), and in 2012, 1730 (86%) inhabitants aged 5 years or more completed a questionnaire and had a skin prick test for atopy.
  
  
  RESULTS
  There was an inverse association between family size and atopy in the village population in 2003; the prevalence of atopy was the highest for those with no siblings (15.2%) and decreased to 5.4% for those with three and more siblings (OR = 0.22; 0.07-0.66). In contrast, there was little or no such protective effect in the town population where the prevalence of atopy was much higher (7.3% in the villages, 20.0% in the town). Nine years later, the prevalence of atopy had increased in the village to be similar to that in the town (19.6% and 19.9% respectively), and the protective effects of family size and birth order in the villages were much weaker (OR = 0.64; 95% CI 0.33-1.27 for three or more siblings). Both protective effects were strongest among children.
  
  
  CONCLUSIONS
  The protective effects of family size and birth order on atopy were much stronger in children than in adults and among those living in a village. They largely disappeared with the steep increase in atopy prevalence at all ages; this followed environmental changes on the village farms.
authors.affiliation: 1st Department of Pediatrics, Allergology and Cardiology, Wroclaw Medical University, Wroclaw, Poland.
authors.forename: B
authors.initials: B
authors.lastname: Sozańska
authors.affiliation: London School of Hygiene and Tropical Medicine, London, UK.|Centre for Public Health Research, Massey University, Wellington, New Zealand.
authors.forename: N
authors.initials: N
authors.lastname: Pearce
authors.affiliation: Faculty of Sociology, University of Wrocław, Wrocław, Poland.
authors.forename: M
authors.initials: M
authors.lastname: Błaszczyk
authors.affiliation: 1st Department of Pediatrics, Allergology and Cardiology, Wroclaw Medical University, Wroclaw, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Boznański
authors.affiliation: Imperial College (NHLI) and Royal Brompton Hospital, London, UK.
authors.forename: P
authors.initials: P
authors.lastname: Cullinan
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000383:Agriculture; D001722:Birth Order; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005191:Family Characteristics; D005260:Female; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D011044:Poland / Q000453:epidemiology; D015995:Prevalence; D065840:Protective Factors; D012424:Rural Population; D035781:Siblings; D012882:Skin Tests; D055815:Young Adult
keywords: atopy; birth order; farming; siblings