Lifetime dog and cat exposure and dog- and cat-specific sensitization at age 18 years

Background Prior research about whether keeping a dog or cat at home causes allergies to that pet has been limited to outcomes in early childhood. Objective Evaluate the association between lifetime dog and cat exposure and allergic sensitization to the specific animal at 18 years of age. Methods Participants enrolled in the Detroit Childhood Allergy Study birth cohort during 1987-1989 were contacted at the age 18 years. Sensitization to dog or cat was defined as animal-specific IgE >= 0.35 kU/L. Annual interview data from childhood and follow-up interviews at age 18 years were used to determine lifetime indoor dog and cat exposure (indoor was defined when the animal spent >50% of their time inside the house). Exposure was considered in various ways: first year, age groups and cumulative lifetime. Analyses were conducted separately for dogs and cats. Results Among males, those with an indoor dog during the first year of life had half the risk [relative risk (RR) = 0.50, 95% confidence interval (CI) 0.27, 0.92] of being sensitized to dogs at age 18 compared with those who did not have an indoor dog in the first year. This was also true for males and females born via c-section (RR = 0.33, 95% CI 0.07, 0.97). Overall, teens with an indoor cat in the first year of life had a decreased risk (RR = 0.52, 95% CI 0.31, 0.90) of being sensitized to cats. Neither cumulative exposure nor exposure at any other particular age was associated with either outcome. Conclusions and Clinical Relevance The first year of life is the critical period during childhood when indoor exposure to dogs or cats influences sensitization to these animals.