Background: The prevalence of allergic sensitization and allergic diseases has increased for decades in Northern Europe, but recent studies are lacking.

Objective: We sought to study the prevalence trends of allergic sensitization, associated risk factors, and the association with asthma and allergic rhinitis (AR) among children in Northern Sweden.

Methods: Three cohorts of children aged 7 to 8 years participated in a skin prick test (SPT) with 10 airborne allergens in 1996, 2006, and 2017, with 2148, 1693, and 1762 participants tested, respectively, representing 87% to 90% of schoolchildren in the catchment communities. Adjusted Poisson regression was used to identify risk factors for allergic sensitization and the association with asthma and AR.

Results: The prevalence of any positive SPT response increased from 21% in 1996 to 30% in 2006 and remained at 30% in 2017 (P <.001). Sensitization to cat was the most common for all the years. The risk factor pattern for a positive SPT response was similar in all examinations, with positive and significant associations with a family history of allergy (risk ratio, 1.4-1.5) and negative and significant associations with having a cat at home (risk ratio, 0.7-0.8). The prevalence of physician-diagnosed asthma increased, but the association with allergic sensitization weakened. The opposite trends were found for AR—decreasing prevalence and strengthened association with allergic sensitization.

Conclusions: The prevalence of allergic sensitization increased from 1996 to 2006 but plateaued in the next decade, whereas the risk factor pattern remained stable. The diverging trends of associations between allergic sensitization and asthma and AR suggest secular trends in the clinical management of allergic diseases.

BACKGROUND: Time trends of incidence of allergic sensitization are unknown and recent trends of prevalence and risk factors are lacking.

OBJECTIVE: To estimate the incidence, prevalence, remission, risk factors, and time trends for allergic sensitization among schoolchildren followed from age 7 to 8 years to age 11 to 12 years.

METHODS: In 2006, all children in grades 1 and 2 aged 7 to 8 years in 2 municipalities in northern Sweden were invited to a questionnaire survey and to skin prick testing to 10 common airborne allergens. The cohort was reexamined in 2010, with additional blood sampling for specific IgE. Participation rates were 90% (n = 1700) at age 7 to 8 years and 85% (n = 1657) at age 11 to 12 years. The results were compared with a cohort examined by identical methods 10 years earlier.

RESULTS: The prevalence of positive skin prick test result to any allergen increased from 30% at age 7 to 8 years to 41% at age 11 to 12 years (P < .001). The cumulative 4-year incidence was 18%, while remission was low. Sensitization to pollen and furred animals was most common. A family history of allergy was significantly associated with incident sensitization, whereas the presence of furred animals at home was negatively associated. The prevalence at age 7 to 8 years and at age 11 to 12 years and the 4-year incidence were all significantly higher compared with the cohort examined 10 years earlier.

CONCLUSIONS: The prevalence of allergic sensitization increased by age as a consequence of a high incidence and a low remission. The trends of increasing incidence and prevalence among schoolchildren imply future increases in the prevalence of allergic diseases.

Background: Allergic sensitization increases the risk of asthma and allergic rhinitis, but the impact of age at onset of sensitization is less studied.

Objective: To examine the cumulative incidence of asthma and rhinitis up to age 19 years in relation to age at onset of sensitization to airborne allergens.

Method: All children in grade 1 and 2 (median age, 8 years) in 2 municipalities in Northern Sweden were invited to undergo skin prick tests and answer a questionnaire about allergic diseases, and 88% participated. At ages 12 and 19 years, the protocol was repeated, and 1510 individuals participated in all 3 examinations. Specific IgE data were collected in a random sample at age 19 years (n = 770). Onset of sensitization was defined: 8 years or less, 8 to 12 years, 12 to 19 years, and never sensitized. Adjusted Poisson regression was used to calculate risk ratios (RRs).

Results: At 19 years, those sensitized at 8 years of age or earlier had the highest risk of asthma (RR, 4.68; 95% CI, 3.15-6.97) and rhinitis (RR, 22.3; 95% CI, 13.3-37.6), and 84% had developed either asthma or rhinitis. The combination of sensitization at age 8 years or earlier and family history of allergic diseases rendered high risks for asthma (RR, 10.6; 95% CI, 6.71-16.7) and rhinitis (RR, 36.3; 95% CI, 18.9-69.7). Individuals sensitized at age 8 years or earlier showed significantly highest level of sensitization, as judged by number of positive skin test results and titers of specific IgE.

Conclusions: Most individuals with sensitization at age 8 years or earlier developed asthma or rhinitis before young adulthood. The high level of sensitization in those sensitized early contributes to the high incidence of allergic airway conditions.