Is cat-keeping the main determinant of new-onset adulthood cat sensitization? Reply

We thank Liccardi et al for their comments on our article dealing with new-onset cat sensitization in adults.We maintain that cat-keeping and allowing a cat in the bedroom are the main determinants of indoor cat allergen levels in the general European population, as shown by a previous European Community Respiratory Health Survey (ECRHS) study (reference 10 of our article). Cat allergen levels in the mattress were 200 times higher in cat-keeping homes (geometric mean, 61.4 mg/g; 95% CI, 48.4-77.9) with respect to nevercat-keeping homes (geometric mean, 0.29 mg/g; 95% CI, 0.27-0.31). Moreover, log-transformed geometric mean of Fel d 1 was 10 times lower when the cat was not allowed inside the house and 4 to 5 times lower when the cat was not allowed inside the bedroom. Liccardi et al reported similar conclusions in a review.The modalities of cat exposure proposed by Liccardi et al could be useful to detail the level of cat allergen exposure. However, the category ‘‘direct contact elsewhere’’ could lead to the same level of cat exposure as ‘‘direct domestic contact,’’ as in domestic cleaners in houses with cats, or could stand for occasional contact with cats in friends’ or relatives’ houses. This classification would need careful validation.We acknowledge that cat sensitization can also occur without direct cat exposure. However, we maintain that cat ownership is one of the main determinants of cat sensitization in adulthood. After examining Table I in a publication by Liccardi et al, we found that it shows strong support for our conclusions; in 1665 patients evaluated in an Allergy Service, direct exposure to cat was present in 52.4% of the people sensitized to cat but only in 2.1% of the people not sensitized—(148-118)/(1665-225)=2.1%(P<.001). Anyway, to cope with indirect exposure to cat allergen, in multivariable analysis we adjusted for community prevalence of cat ownership.In conclusion, cat ownership is the main determinant of cat allergen levels in dwellings. Acquiring a cat is a risk factor for new-onset cat sensitization in adults, even after controlling for 12 other factors, although we cannot exclude other known or unknown risk factors.