Ownby DR, Johnson CC, Peterson EL. JAMA. 2002;288:963–972
Purpose of the Study.
To determine if there is an association between pet exposure in the first year of life and allergy sensitization at age 6 to 7 years.
A prospective birth cohort enrolled from a health maintenance origination in suburban Detroit. Enrolled infants were born between 1987–1989, and followed yearly through age 7 years. Of the 835 enrolled infants, 474 completed the protocol.
After enrollment, families were interviewed for allergic histories. At age 1, the parents were contacted, and the number and type of pet(s) in the home in the first year was determined. That number of cats and dogs was used as the reference for the study. At ages 2 and 4 a home visit for dust mite and cat dust samples was performed. Phone visits were done at ages 3, 5, and 6. At 6 to 7 years skin tests for allergens, serum immunoglobulin E (IgE), radioallergosorbent testing (RAST), asthma histories and medication use, pulmonary function, and methacholine challenges were done. The results were tested to determine if any of three levels of pet exposure affected any allergic and/or asthmatic condition: 0 pets, 1 dog or cats, 2 or more dogs or cats.
Using either skin test or RAST as a measure of atopy, there was a protective effect for developing atopy at age 6 to 7 years as the level of exposure of dogs increased (≥2 dogs more protective than 1 dog). Asthma development was not attenuated by dog exposure. As the number of dogs and cats increased, the development of atopy to indoor and/or outdoor allergens decreased; however, asthma did not decrease. The exposure to pets at age 6 or 7 had no influence on the findings.
Few studies have raised as many questions from both patients and physicians as has this one. In large part, patients (and parents) are looking for any conceivable excuse to keep their pets. In practical terms, if a child is already allergic to pet and nonpet allergens, there is no benefit in keeping their pets. If a child is allergic to nonpet allergens but not pets, there is no help in acquiring a pet, but it’s not necessary to eliminate an existing pet. If a child has asthma and is pet-allergic, the pet should be removed from the home. If a newborn is joining a household with a pet(s), then and only then will dog or multiple pet exposure provide potential benefit. If a child does develop pet allergies or nonpet allergies before age 7, the above recommendations then prevail.