Distribution, aerodynamic characteristics, and removal of the major cat allergen Fel d 1 in British homes

Background - Sensitisation to cat allergen (Fel d 1) is an important risk factor for asthma in the UK. A study was undertaken to investigate the distribution of cat allergen in British homes, the aerodynamic characteristics and particle size distribution of airborne Fel d 1, and the method of removing it. Methods - Dust was collected from 50 homes with a cat and from 50 homes without a cat, and airborne levels of Fel d 1 were measured in 50 homes with a cat and 75 homes without a cat. Particle size distribution was determined using an Andersen sampler (8 hours/day) in 10 homes with cats. This was repeated on five separate days in a house with four cats, and then one, two, four, seven, and 14 days after the cats were removed from the living room area. The effect of high efficiency particulate air (HEPA) cleaner on airborne levels of Fel d 1 was investigated in seven homes with cats. Samples were collected on two separate days from two rooms of each house concurrently, one of which contained the cat, one day with the HEPA cleaner on and the other day as a control. Three one hourly samples were collected over a nine hour period (baseline, 4-5 hours, 8-9 hours) using a high volume dust sampler (air flow rate 60 l/min) and the air sample was collected onto a microglass fibre filter (pore size 0.3 μm). Results - Fel d 1 concentrations were much lower in houses without a cat than in those with a cat (260-fold difference (95% CI 167 to 590) in living room carpets: geometric mean (GM) 0.9 μg/g (range 0.06-33.93) versus 237 μg/g (range 2.8- 3000); 314-fold difference (95% CI 167 to 590) in upholstered furniture: 1.21 μg/g (range 0.06-61.9) versus 380 μg/g (range 7.1-6000); 228-fold difference (95% CI 109 to 478) in bedroom carpets: 0.24 μg/g (range 0.06- 2.24) versus 55 μg/g (range 0.06-2304); and 215-fold difference (95% CI 101 to 456) in mattresses: 0.2 μg/g (range 0.06-2.3) versus 55 μg/g (range 0.06-3400)). Airborne levels of Fel d 1 were detected in all houses with cats, and the levels varied greatly between the homes (range 0.7-38 ng/m3). Low concentrations of airborne Fel d 1 (range 0.24-1.78 ng/m3) were found in 22 of 75 homes without a cat. Although airborne Fel d 1 was mostly associated with large particles (>9 μm, approximately 49% of the allergen recovered), small particles (4.8 μm) which fell to 13% of their baseline level. Fel d 1 levels associated with small particles (