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 r isk factor for asthma in the UK. A study was undertaken to investigate the distribution of cat allergen in British homes, the aerodynamic ch aracteristics 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 col lected 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 ov er a nine hour period (baseline, 4-5 hours, 8-9 hours) using a high vo lume dust sampler (air flow rate 60 l/min) and the air sample was coll ected onto a microglass fibre filter (pore size 0.3 mu m). Results - F el 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 ro om carpets: geometric mean (GM) 0.9 mu g/g (range 0.06-33.93) versus 2 37 mu g/g (range 2.8-3000); 314-fold difference (95% CI 167 to 590) in upholstered furniture: 1.21 mu g/g (range 0.06-61.9) versus 380 mu g/ g (range 7.1-6000); 228-fold difference (95% CI 109 to 478) in bedroom carpets: 0.24 mu g/g (range 0.06-2.24) versus 55 mu g/g (range 0.06-2 304); and 215-fold difference (95% CI 101 to 456) in mattresses: 0.2 m u g/g (range 0.06-2.3) versus 55 mu g/g (range 0.06-3400)). Airborne l evels of Fel d 1 were detected in all houses with cats, and the levels varied greatly between the homes (range 0.7-38 ng/m(3)). Low concentr ations of airborne Fel d 1 (range 0.24-1.78 ng/m(3)) were found in 22 of 75 homes without a cat. Although airborne Fel d 1 was mostly associ ated with large particles (>9 mu m, approximately 49% of the allergen recovered), small particles (<4.7 mu m) comprised approximately 23% of the total airborne allergen. total airborne Fel d 1 was reduced by 61 .7% two days after removal of the cat but this was due predominantly t o the decrease in larger particles (>4.8 mu m) which fell to 13% of th eir baseline level. Fel d 1 levels associated with small particles (<4 .8 pm) remained largely unchanged on days 1, 2 and 4 and then slowly d ecreased to 33% of the baseline levels at day 14. With HEPA cleaner a significant reduction in airborne Fel d 1 was observed compared with t he control sampling (GM. 5.04-0.88 ng/m(3) versus 3.79-1.56 ng/m(3) at baseline and 8 hours, active versus control group; p=0.008). Conclusi ons - Airborne Fel d 1 was detectable in undisturbed conditions in all homes with cats and in almost a third of homes without cats. in house s with cats a significant proportion (23%) of airborne Fel d 1 was ass ociated with small particles (<4.7 mu m diameter). Removal of the cat from the living room and bedroom areas of the home and the use of HEPA air cleaner reduced airborne levels of cat allergen in homes with cat s, but the reduction following cat removal was not evenly spread acros s the particle size range.