Patients With Any Allergy May be Dogged by Cats

LONDON, July 2 -- Cats may trigger an asthmatic airway response even in patients not specifically allergic to cat dander, researchers found.

In a population-based study, cat dander in the home caused the same bronchial responsiveness in adults sensitized to house dust mite, timothy grass, or Cladosporium mold as in those sensitized to cat (response slope -0.29 versus -0.31), reported Susan Chinn, D.Sc., of Imperial College London, and colleagues.

The results were unexpected but have implications for a large population, they said in the first July issue of the American Journal of Respiratory and Critical Care Medicine.

"Cat allergen exposure at moderate levels may be harmful to all atopic adults," they wrote.

"The clinical implication is that it is insufficient to test patients with asthma for cat sensitization," they said, adding, "advice should be against cat ownership in those showing sensitization to any allergen."

The researchers analyzed data from 1,884 participants in 20 centers across Europe in the larger European Community Respiratory Health Survey.

The participants (ages 27 to 56) completed a survey, had blood drawn for immunoglobulin E (IgE) sensitization testing, and had their mattress tested for house dust mite Der 1 and cat Fel d 1 allergen. Their bronchial responsiveness to methacholine, "the objective measure of choice in epidemiological studies on asthma," was also measured.

Overall, 31.6% of men and 24.6% of women were sensitized to any of the four allergens.

The largest proportion of men and women were sensitized to house dust mite (18.5% and 13.4%, respectively) and to timothy grass (16.7% and 14.0%, respectively) though a few showed sensitization to Cladosporium (1.3 and 0.8% respectively).

About 9% of men and 8.3% of women were sensitized to cat allergen. The prevalence of cat ownership varied from less than 10% among participants in Spain to more than 35% in the United Kingdom.

Cat allergen, though, was ubiquitous, the researchers said. Exposure to cat allergen, as measured in mattresses, was detectable for 76.7% of men and 82.3% of women. And, 17.4% of men and 22.3% of women were exposed to the highest Fel d 1 levels above 8 g/g.

House dust mite exposure was not associated with asthmatic bronchial response (P=0.870), even with increasing exposure (P=0.562 for trend).

In the overall group, cat allergen exposure was not significantly linked to bronchial response (P=0.298), though there was a significant trend for greater response with increasing exposure (P=0.033 for trend).

The difference between the highest and lowest cat allergen exposure groups corresponded to approximately -0.62 the methacholine doubling dose required to produce a 20% fall in lung function as measured by forced expiratory volume in one second (FEV₁).

Participants without cats in the home showed only a weak association of bronchial response with cat allergen level. Overall, those who were exposed but not sensitized to cat showed only a marginally significant trend in bronchial response with exposure level (P=0.040).

However, bronchial response trends were similar for atopic patients in general as for those sensitized to cat. The bronchial response slopes were:

• -0.31 for those sensitized to cat (95% confidence interval -0.56 to -0.05, P=0.017).
• -0.30 for those sensitized to any one of the four allergens tested for -- cat, house dust mite, timothy grass, or Cladosporium (95% CI 0.45 to -0.16, P

The researchers cautioned that not all the subgroup analyses and interaction tests done in the analysis were preplanned. Furthermore, cat allergen exposure or cat ownership may be a proxy for increased endotoxin exposure leading to increased bronchial responsiveness, they said.

"We cannot rule out this explanation in the current data," they wrote.

Although the findings fit with prior research reporting a strong link between asthma and indoor allergens, the interaction between sensitization of any kind and current exposure to a specific allergen was unexpected, they said.

Studies had only suggested that patients with specific sensitizations exhibit greater bronchial response to the allergens to which they are sensitized.

"Our results suggest that avoidance of exposure to cat allergen and cats may be beneficial in terms of bronchial responsiveness for a wider group of individuals than previously anticipated," Dr. Chinn and colleagues wrote.

Although many studies attempting to reduce allergen exposure for in adults with asthma have targeted mite allergens, "our results suggest that this may be less important for adults than reduction of cat allergen exposure, even for individuals not sensitized to cat," they added.