Heredity, pet ownership, and confounding control in a population-based birth cohort.
BACKGROUND
The association between pet ownership in childhood and subsequent allergic disease is controversial. Bias related to selection of pet exposure has been suggested as a reason for contradictory study results.


OBJECTIVE
The purpose of this investigation was to elucidate how pet exposure depends on family history of allergic disease, smoking, and socioeconomic factors in a prospective birth cohort.


METHODS
Parents of 4089 two-month-old children answered a questionnaire that included detailed questions about family history of asthma (maternal, paternal, and sibling), rhinoconjunctivitis, atopic eczema/dermatitis syndrome, pollen and pet allergy, smoking habits, parental occupation, and family pet ownership (cat and dog). Dust samples collected from the mothers' beds were analyzed for Fel d 1 and Can f 1 in a subgroup of the cohort.


RESULTS
Cats were less frequently kept in families with parental asthma, rhinoconjunctivitis, or pet or pollen allergy (3.5% to 5.8%) than in families without parental allergic disease (10.8% to 11.8%). Dogs were less common in families with (3.3%) than in families without (5.9%) parental atopic eczema/dermatitis syndrome. Families with smoking mothers and those with low socioeconomic index kept cats and dogs more frequently. Cat allergen levels were lower in homes with than in homes without maternal pet allergy, and this tended to hold true even for homes without a cat. Cat ownership decreased from birth to 2 years of age, especially in families with parental history of allergic diseases.


CONCLUSIONS
There seems to be a selection of pet exposure based on parental history of allergy, maternal smoking, and socioeconomic factors. This has to be taken into consideration in evaluations of risk associations between pet exposure and allergic disease in childhood.
Almqvist
Catarina
C
Department of Occupational and Environmental Health, Karolinska Hospital, Stockholm, Sweden.
Egmar
Ann-Charlotte
AC
van Hage-Hamsten
Marianne
M
Berglind
Niklas
N
Pershagen
Göran
G
Nordvall
S Lennart
SL
Svartengren
Magnus
M
Hedlin
Gunilla
G
Wickman
Magnus
M
D000818:Animals; D000829:Animals, Domestic / Q000276:immunology*; D015331:Cohort Studies; D006801:Humans; D006967:Hypersensitivity / Q000209:etiology* / Q000235:genetics; D007223:Infant; D015999:Multivariate Analysis; D011446:Prospective Studies; D012907:Smoking / Q000009:adverse effects; D012959:Socioeconomic Factors