Pets and Respiratory Disease in Infancy

William T. Basco, Jr., MD, MS


October 23, 2012

Respiratory Tract Illnesses During the First Year of Life: Effect of Dog and Cat Contacts

Bergroth E, Remes S, Pekkanen J, Kauppila T, Bϋchele G, Keski-Nisula L
Pediatrics. 2012;130:211-220

Animal Exposure and Human Respiratory Disease

Risk factors associated with respiratory tract illnesses during childhood include parental history of asthma or current smoke exposure. Conversely, some studies have suggested that exposure to animals -- dogs, but not cats -- may reduce the risk for asthma or atopic disease.

This study used a prospective birth cohort from Finland to evaluate the effect of domestic animal contact on the frequency of respiratory tract infection during the first year of life. This birth cohort included 208 children whose mothers lived in rural areas, classified as either a farming or a nonfarming environment. An additional 218 children who lived in either rural or suburban environments also provided data for the study.

The children were born between 2002 and 2005. Health and illness data, as well as exposure data, were obtained from diaries completed by the parents through the first year of the child's life. Each week, parents recorded the frequency of cough, wheezing, rhinitis, elevated temperature, presence of middle ear infection, diarrhea, or other illness-associated symptoms during the previous 7 days. The parents of 397 children provided adequate data for analysis.

Reported dog and cat indoor contacts in the home were classified as follows:

  • No contact;

  • Contact for up to 6 hours per day;

  • Contact for 6-16 hours per day; or

  • Contact for > 16 hours per day.

The analyses also accounted for breastfeeding, birth month, birthweight, number of siblings, and history of parental atopic disease.

Significant group differences were found among children and parents living in rural, nonfarming, and suburban environments. For example, the average number of siblings of suburban children was 0.8, compared with 1.4 in children who lived on a farm. Among parents of suburban children, 69% had atopic disease compared with only 46.5% of the parents who lived in rural settings. Educational levels were higher among suburban parents, but so was the frequency of maternal smoking during infancy. Suburban children were more likely to attend daycare.

With respect to pets, 24.6% of suburban families had a dog inside the home, compared with 35% of farm families. Similar differences were reported for the presence of a cat inside the home. Overall, 62% of the children had some contact with a dog, and 34% with a cat.

In multivariate analyses, children who had experienced dog contact in the home were more likely to be healthy during the previous week, with an adjusted odds ratio of 1.31 (95% confidence interval, 1.13-1.52). These children were also significantly less likely to have a fever or to have received antibiotics. By comparison, in the adjusted analysis, cat exposure was not associated with being healthy or with any of the disease states. Bergroth and colleagues concluded that dog and cat contact during early infancy may reduce overall morbidity, specifically by leading to fewer respiratory tract symptoms.


This study raises some interesting issues, and it echoes data I reviewed in 2011. In one of the top 5 viewpoints for that year, I reviewed a reanalysis of 2 European cohort studies[1] that looked at the extent of microbial exposure in children who lived on farms; it showed that as the number of microbes in the child's household environment increased, the child was less likely to develop asthma or evidence of atopy (allergic antibodies).

That dose/response affect was shown in a cohort of children living in farm settings. Bergroth and colleagues included children from suburban settings, and it is clear that the parents of those children are very different, especially in their propensity toward having atopic disease. Therefore, I am still a little concerned that Bergroth and colleagues' study did not eliminate the biases inherent in a design that doesn't randomly assign children and parents to farm or other habitations. For example, parents who cannot withstand frequent animal exposure might choose to live in suburban rather than a farm environment. Such parents are also less likely to have indoor pets, and their children are more likely to be atopic.

This multiple-level confounding could have been managed with propensity scores for where the children live. That said, the data are also broadly consistent with other studies that have raised the issue of the "hygiene hypothesis," which suggests that overly sterile living environments during young childhood have in part contributed to the worldwide rise in atopic disease. It's an interesting and evolving area in the literature, and this study certainly adds to the evidence.

On a practical level, these data suggest that if pediatric providers are advising families about whether to have indoor pets, families might consider dogs over cats, but many other factors go into the decision of whether to have a household pet.