Etiologic role of unapparent exposure in cat allergy

To determine the importance of unnoticed exposure to cat, we studied 20 patients with a history of respiratory allergy. All the patients had a positive prick test to cat dander extract, and none of them kept cats as pets. The prick test was carried out with a dander extract from cat at a concentration of 100 BU/ml. The specific IgE was determined by the commercially available Pharmacia CAP System. We carried out a conjunctival challenge test. The concentration of Fel d 1 was quantified in dust samples from the patients' homes by a commercially available method. The patients were reassessed in order to establish a relation between exposure and symptoms, and concealed allergen sources. Sixteen patients showed significant levels of Fel d 1 in their homes (mean of 3.35 micrograms/g of dust). The conjunctival challenge test was positive in 15 patients. These patients showed an exposure mean of 0.4 microgram/g of dust. The mean levels of specific serum IgE were higher in those patients with a positive challenge than in those with a negative challenge (P = 0.0145). In nine reassessed patients, a relation was established between natural exposure and the onset of the symptoms. A possible hidden allergen source was established in 11 patients.(ABSTRACT TRUNCATED AT 250 WORDS)