title: Increase in pollen sensitization in Swedish adults and protective effect of keeping animals in childhood.
abstract: To date, most studies of the 'allergy epidemic' have been based on self-reported data. There is still limited knowledge on time trends in allergic sensitization, especially among adults.
  
  
  
  To study allergic sensitization, its risk factors and time trends in prevalence.
  
  
  
  Within West Sweden Asthma Study (WSAS), a population-based sample of 788 adults (17-60 years) underwent skin prick tests (SPTs) for 11 aeroallergens 2009-2012. Specific IgE was analysed in 750 of the participants. Those aged 20-46 years (n = 379) were compared with the European Community Respiratory Health Survey sample aged 20-46 year from the same area (n = 591) in 1991-1992.
  
  
  
  Among those aged 20-46 years, the prevalence of positive SPT to pollen increased, timothy from 17.1% to 29.0% (P < 0.001) and birch from 15.6% to 23.7% (P = 0.002) between 1991-1992 and 2009-2012. Measurements of specific IgE confirmed these increases. Prevalence of sensitization to all other tested allergens was unchanged. In the full WSAS sample aged 17-60 years, any positive SPT was seen in 41.9%, and the dominating sensitizers were pollen (34.3%), animals (22.8%) and mites (12.6%). Pollen sensitization was strongly associated with rhinitis, whereas indoor allergens were more associated with asthma. Growing up with livestock or furred pets decreased the risk of sensitization, adjusted odds ratio 0.53 (0.28-0.995) and 0.68 (0.47-0.98), respectively.
  
  
  
  Pollen sensitization has increased in Swedish adults since the early 1990s, while the prevalence of sensitization to other allergens has remained unchanged. This is one plausible explanation for the increase in rhinitis 1990-2008 in Swedish adults, during which time the prevalence of asthma, which is more associated with perennial allergens, was stable. Contact with animals in childhood seems to reduce the risk of sensitization well into adulthood. One major factor contributing to the rise in pollen allergy is a significant increase in levels of birch and grass pollen over the past three decades.
authors.affiliation: Krefting Research Centre, Department of Internal Medicine and Clinical Nutrition, Gothenburg University, Göteborg, Sweden. anders.bjerg-backlund@karolinska.se.|Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden. anders.bjerg-backlund@karolinska.se.
authors.forename: A
authors.initials: A
authors.lastname: Bjerg
authors.affiliation: Krefting Research Centre, Department of Internal Medicine and Clinical Nutrition, Gothenburg University, Göteborg, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Ekerljung
authors.affiliation: Krefting Research Centre, Department of Internal Medicine and Clinical Nutrition, Gothenburg University, Göteborg, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Eriksson
authors.affiliation: Krefting Research Centre, Department of Internal Medicine and Clinical Nutrition, Gothenburg University, Göteborg, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Näslund
authors.affiliation: ImmunoDiagnostics, ThermoFisher Scientific, Uppsala, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Sjölander
authors.affiliation: Krefting Research Centre, Department of Internal Medicine and Clinical Nutrition, Gothenburg University, Göteborg, Sweden.|Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine, the OLIN Unit, Umeå, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: Rönmark
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Göteborg, Sweden.
authors.forename: Å
authors.initials: Å
authors.lastname: Dahl
authors.affiliation: Department of Otorhinolaryngology, Sahlgrenska University Hospital, Göteborg, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Holmberg
authors.affiliation: Krefting Research Centre, Department of Internal Medicine and Clinical Nutrition, Gothenburg University, Göteborg, Sweden.|Department of Pediatrics, Gothenburg University, Gothenburg, Sweden.
authors.forename: G
authors.initials: G
authors.lastname: Wennergren
authors.affiliation: Department of Public Health and Community Medicine, Sahlgrenska Academy, Gothenburg University, Gothenburg, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Torén
authors.affiliation: Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden.|Department of Women's and Children's Health, Uppsala University, Uppsala, Sweden.
authors.forename: M P
authors.initials: MP
authors.lastname: Borres
authors.affiliation: Krefting Research Centre, Department of Internal Medicine and Clinical Nutrition, Gothenburg University, Göteborg, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Lötvall
authors.affiliation: Krefting Research Centre, Department of Internal Medicine and Clinical Nutrition, Gothenburg University, Göteborg, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Lundbäck
mesh_terms: D000293:Adolescent; D000328:Adult; D000485:Allergens / Q000276:immunology*; D000818:Animals; D002648:Child; D002675:Child, Preschool; D015897:Comorbidity; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D007114:Immunization; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D057805:Pets / Q000276:immunology*; D011058:Pollen / Q000276:immunology*; D015995:Prevalence; D006255:Rhinitis, Allergic, Seasonal / Q000175:diagnosis / Q000453:epidemiology* / Q000276:immunology*; D012306:Risk; D012882:Skin Tests; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
chemical_list: D000485:Allergens
keywords: adults; allergic sensitization; asthma; epidemiology; farm; skin prick test; specific IgE