Inverse association between rural environment in infancy and sensitization to rodents in adulthood

Background: It is not known whether early childhood exposure to hygiene hypothesis factors modifies the risk of sensitization to aeroallergens among adults. Studying adults exposed to allergens in the workplace may help determine whether childhood exposures confer lasting protection against sensitization. Objective: To determine whether early life exposures influence the prevalence of sensitization to allergens in adulthood. Methods: Sensitization to rodents was determined by skin testing in a cross-sectional study among university employees with and without occupational exposure to laboratory animals. Demographic information was obtained by questionnaire. Results: Of 137 employees, 8% of workers without occupational exposure to laboratory animals and 24% of those with such exposure were sensitized to rodents (P = .007). None of 32 study participants who lived in a rural environment during their first year of life were rodent sensitized vs 18% of those who lived in other settings (P < .01). Rural setting in infancy was also associated with a decreased prevalence of sensitization to outdoor allergens (odds ratio [OR], 0.36; 95% confidence interval [CI], 0.14-0.95). After adjusting for multiple confounders, sensitization to rodents remained rare among individuals who lived in a rural setting during infancy (OR, <0.15). Rodent sensitization was more prevalent among those with higher educational attainment (OR, 9.50; 95% CI, 1.10-82.02) and those sensitized to indoor allergens (OR, 6.22; 95% CI, 1.42-27.24). Sensitization to rodents was not significantly associated with having older siblings or sensitization to outdoor allergens. Conclusions: Living in a rural setting during the first year of life is associated with protection from sensitization to rodent allergens in the workplace decades later.