Maternal history influences risk of asthma in children exposed to cats

While beneficial for many, cat exposure may triple the risk of asthma in some children

Thursday, September 5, 2002

Researchers at Brigham and Women’s Hospital (BWH) have found that among children with a maternal history of asthma, exposure to cat allergens may increase the risk of developing asthma. After years of advising families with allergies to avoid pets, this research provides a new outlook on which children may be at the greatest risk, and helps identify those whose health may actually benefit from having a cat at home. These findings will be published in the September 7, 2002 issue of the Lancet.

"Parental history has been known to influence pet allergies in children, and for many years it was thought that cat exposure actually increased a child’s asthma risk," said the principal investigator of the Home Allergens and Asthma study, Diane Gold, MD, MPH, of BWH. "In our research we found that the relationship between exposure to cat allergen in early life and wheezing in the first five years of life is modified by whether the child’s mother has asthma or not."

Recent studies have gathered evidence that cat exposure during infancy can be protective against asthma. The BWH research confirms these findings in all but one situation: when the child's mother has asthma.

In this study, researchers found that in the group of children with non-asthmatic mothers, those exposed to a cat were 40 percent less likely to experience persistent wheezing as compared to those with no cat exposure. This risk reduction remained consistent from the ages of 1 to 5 years. Among children with a maternal history of asthma, the risk of wheezing associated with exposure to a cat increased with age. By the age of three years, children with exposure to a cat in early life were twice as likely to suffer from wheezing and by the age of five, more than three times as likely. The findings suggest that children of asthmatic mothers become more readily sensitized to cat allergen and wheeze when exposed to it.

"This research reinforces our knowledge that for the vast majority of children, having a cat in the home during their developmental years can be beneficial by protecting against asthma and allergies," said Juan Celedon, M.D., DrPH, of BWH and lead author of the study. "It is only among a high-risk group - children with a maternal history of asthma and perhaps, those whose mothers are allergic to cats - that exposure to a cat can negatively impact respiratory health."

Allergies affect two of every 10 Americans. Asthma, a common allergic reaction, is the most prevalent chronic childhood disease in America and the number one reason for hospitalization.

The study followed 448 children with a family history of allergic diseases from birth to age five. Through periodic telephone interviews with caretakers, the researchers gathered information on the children’s exposure to pets and on how often the children experienced episodes of wheezing. In addition, the researchers tested dust samples from each child’s home for levels of cat allergen. The researchers then analyzed the data they collected, adjusting for factors such as sex, household income, and day-care attendance.

The study was supported by grants from the National Institutes of Health.

BWH is a 716-bed nonprofit teaching affiliate of Harvard Medical School and a founding member of Partners HealthCare System, an integrated health care delivery network. Internationally recognized as a leading academic health care institution, BWH is committed to excellence in patient care, medical research, and the training and education of health care professionals. The hospital's preeminence in all aspects of clinical care is coupled with its strength in medical research. A leading recipient of research grants from the National Institutes of Health, BWH conducts internationally acclaimed clinical, basic and epidemiological studies.

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