AIRBORNE CONCENTRATIONS AND PARTICLE-SIZE DISTRIBUTION OF ALLERGEN DERIVED FROM DOMESTIC CATS (FELIS-DOMESTICUS) - MEASUREMENTS USING CASCADE IMPACTOR, LIQUID IMPINGER, AND A 2-SITE MONOCLONAL-ANTIBODY ASSAY FOR FEL-D-I

The recent development of a sensitive two-site monoclonal antibody immunoassay for the major cat allergen (Fel d I) had made it possible to make accurate measurements of airborne cat allergen using low volume samplers that do not disturb the room. Houses with cats had from 2 to 20 ng Fel d I/m3 air compared with < 0.2 ng/m3 in houses without cats. Using a cascade impactor and a multistage liquid impinger, the particle size distribution of airborne Fel d I in nine houses was 75% on particles ≥ 5 μm in diameter and 25% (range, 10 to 62%) on particles ≤ 2.5 μm. In a cat vivarium with 12 cats, the air contained 40 ng Fel d I/m3, but < 2% was detected on particles ≤ 2.5 μm. The air exchange rate in the vivarium (~ 15 changes/h) appears to be the major difference from domestic houses (< 0.5 changes/h). Repeated studies in one house confirmed a very high proportion (~ 60%) of Fel d I on small particles. During domestic cleaning, the levels of small particle allergen in this house approached those produced by a nebulizer for bronchial provocation, i.e., 40 ng/m3. These results show unequivocally that significant airborne Fel d I is associated with small particles, which remain airborne for long periods. These findings are strikingly different from previous results obtained with airborne dust mite allergen. The results provide an explanation for the distinctive rapid onset of asthma or rhinitis in patients allergic to cats and a basis for designing a policy to reduce airborne allergen in houses with cats.