HealthDay News — Very young children who are exposed to dogs are generally healthier and have fewer respiratory infections than those who are not, researchers found, suggesting the pets may help boost immune system development.

During the first year of life, children who lived with dogs were less likely to have frequent ear infections (OR=0.56, 95% CI: 0.38-0.81, P=0.002) and were treated with fewer courses of antibiotics for otitis (OR=0.71, 95% CI: 0.52-0.96, P=0.03) compared with those who did not, Eija Bergoth, MD, of the Kuopio University Hospital in Finland and colleagues found.

“Our results suggest that dog contacts protect children from respiratory tract infections during the first year of life,” the researchers reported in Pediatrics.

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Results from previous studies exploring the effect of pets in the home on children with respiratory infections have been mixed, with some findings indicating a protective effect and others suggesting an increased risk for illness.

To better understand this relationship, Bergroth and colleagues conducted a prospective cohort study involving 397 Finnish newborns. Parents were asked to fill out weekly diaries to record their child’s symptoms, infections and pet exposures starting at week 9 and continuing through the first year of life, as well as a retrospective questionnaire at the study’s conclusion.

The study period included a total 17,124 weeks of follow-up, during which 71.8% of children experienced fever, 39.5% had otitis, 96.7% had rhinitis, 84.4% had cough and 32.2% had wheezing. Among the cohort, 47.6% were prescribed systemic antibiotics.

On the retrospective questionnaire, 65.2% of parents reported that there was no dog at home, whereas 75.5% reported no cat exposure.

Children who had either a dog or cat had better overall health (P<0.001), results of a univariate analysis revealed, with those who had pets in the home experiencing fewer total weeks with respiratory infection symptoms than those without pets.

However, after adjusting for confounders including sex, rural living, maternal smoking, number of siblings, parental allergies and season of birth, the health benefits of pet exposure remained significant only for households with dogs, but not cats. The association for overall health with cat ownership was not significant (OR=1.06, 95% CI: 0.88-1.29, P=0.53).

The researchers also analyzed the effects of length of exposure to dogs on respiratory health for three different time periods — less than six hours per day, six to 16 hours or more than 16 hours — and found the best outcomes among children who lived with dogs that were inside the house for less than six hours per day.

These children had better overall health (OR=1.25, 95% CI: 1.04-1.50, P=0.02), had fewer episodes of fever (OR=0.63, 95% CI: 0.41 to 0.97, P=0.04), took fewer antibiotics (OR=0.54, 95% CI: 0.34-0.87, P=0.01) and had less otitis (OR=0.38, 95% CI: 0.18-0.82, P=0.01) than those exposed to dogs longer than six hours.

Although researchers are not sure what accounts for these differences, they noted that dogs who are outside for longer periods of time may track more dirt into the home, which “is likely to correlate with bacterial diversity in the living environment.” Greater bacterial diversity likely plays a role in immune maturation and infection risk, they added.

Bergroth E et al. Pediatrics. 2012; doi:10.1542/peds.2011-2825.