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Cat Allergy Depends on When You Get the Cat
  By Michael Smith, North American Correspondent, MedPage Today
Published: December 27, 2011

Action Points

· Acquiring a cat as an adult can lead to allergies to cat dander; the risk is lower if one had a cat as a child but higher if allergies were already present.

· Note that adults who get a cat but don't let it in the bedroom appear to be unlikely to become sensitized to the animal.

Thinking of getting a cat? European researchers found that acquiring kitty as an adult can lead to allergies to cat dander.

The risk is lower if you had a cat as a child but higher if you already have some other allergies, according to Giuseppe Verlato, PhD, of the University of Verona in Verona, Italy, and colleagues.

On the other hand, adults who get a cat but don't let it in the bedroom appear to be unlikely to become sensitized to the animal, Verlato and colleagues reported online in the Journal of Allergy and Clinical Immunology.

The bottom line, the researchers concluded, is that "acquiring a cat increases the risk of cat sensitization in adulthood, particularly when the cat is allowed in the bedroom."

The findings come from the European Community Respiratory Health Survey (ECRHS), a large cohort study of asthma conducted from 1991 through 1993. Cat-specific immunoglobulin E was measured in 14,138 of the 18,536 participants.

In the follow-up ECRHS II study, conducted from 1999 through 2002, cat-specific IgE was measured in 7,318 participants, but 828 were already sensitized to cat at baseline. Another 198 were left out because information on cat ownership was missing, leaving 6,292 participants, with an average follow-up of 8.6 years, for the current study.

The aim of the analysis was to determine the risk of new-onset cat sensitization as a function of changes in cat ownership, where sensitization was defined as a serum IgE level of 0.35 kU/L or greater.

Overall, the researchers reported, 4,468 volunteers did not have a cat at either study point, 473 had a cat only at baseline, 651 acquired a cat during the follow-up, and 700 had a cat at both evaluations.

The cat was allowed in the bedroom by 94.3% of the people who had a cat at both surveys and by 92.5% of those who got a cat during the follow-up. Two-thirds of those who got rid of their cat between the surveys (64.1%) had allowed the cat in the bedroom.

Over the follow-up period, 231 people (3.7%) developed sensitivity to cat dander.

Multivariable analysis showed:

· People who got a cat during the follow-up had nearly double the risk of new-onset cat sensitization as did those without a cat at both surveys (1.85, 95% CI 1.23 to 2.78, P=0.017).

· Preexisting allergies to other substances also increased the risk, compared with people who did not have other allergies (RR 2.31, 95% CI 1.74 to 3.07, P<0.001).

· A history of asthma, nasal allergies, and eczema also increased the risk, with relative risks of 1.49, 1.66, and 1.34, respectively.

· Cat ownership in childhood was a protective factor (RR 0.59, 95% CI 0.47 to 0.75, P=0.001).

Interestingly, none of the adults who got a cat but kept the animal out of the bedroom became sensitive to cat dander during follow-up, the researchers reported, compared with 61 of the 1,262 (4.8%) who did let the new cat into the bedroom. The difference was significant at P=0.030, but the study had insufficient power to evaluate the issue in multivariable analysis.

The researchers cautioned that changes over time both in cat ownership and sensitization were assessed at only two points. Also, they noted, the data on pet keeping in childhood were based on retrospective reporting by adults, which could have been affected by recall bias.

Primary source: Journal of Allergy and Clinical Immunology

Source reference:

Olivieri M, et al "Risk factors for new-onset cat sensitization among adults: A population-based international cohort study" J Allergy Clin Immunol 2011; DOI: 10.1016/j.jaci.2011.10.044

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