Clinical aspects of allergic disease Cat antigen in homes with and without cats may induce allergic symptoms

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1 Clinical aspects f allergic disease Cat antigen in hmes with and withut cats may induce allergic symptms Mary Elizabeth Bllinger, D, Peytn A. Egglestn, MD, Elizabeth Flanagan, BS, and Rbert A. Wd, MD Baltimre, Md. Althugh Fel d 1, the majr cat allergen, has been fund in settled dust samples frm hmes bth with and withut cats, the clinical relevance f this allergen has never been studied. In this study we measured airbrne cncentratins f Fel d I in hmes bth with and withut cats and then attempted t relate these levels t thse btained in ur experimental cat challenge mdel t assess their clinical significance. In baseline samples we fund measurable levels f airbrne Fel d 1 in all 37 hmes with cats (range, 1.8 t 578 ng/m3, 9 median, 45.9 ng/m 3) and in 1 f the 4 hmes withut cats (fr detectable samples: range, 2.8 t 88.5 ng/m3, 9 median, 17 ng/m3). Fel d I was present in the settled dust f 38 f 4 hmes withut cats (range, 39 t 375 ng/gm; median, 258 ng/gm), althugh these levels were nly weakly predictive f airbrne levels. Repeat samples btained weekly frm 12 hmes withut cats yielded measurable airbrne Fel d I in at least ne f the fur samples frm all hmes. When cmpared with challenges perfrmed in ur cat rm facility at lw levels f airbrne Fel d 1 (<5 ng/m3), these hme levels are within the range capable f causing upper and lwer respiratry symptms in subjects allergic t cats. We therefre cnclude that the lw level cat expsure that ccurs in many hmes withut cats is capable f inducing symptms in sme patients wh are sensitive t cats. The assessment f cat expsure shuld nt be based slely n the presence r absence f a cat in the hme. (J ALLERGY CLIN IMMUNL 1996;97:97-14.) Key wrds: Cat allergen, envirnmental allergens, animal allergens, antigen challenge Allergic reactins t furred pets are extremely cmmn. Three t ten percent f the general ppulatin and 15% t 4% f atpic individuals are allergic t cats r dgs, with allergy t cats being abut twice as cmmn as allergy t dgs. 1"3 ver half f all hmes in the United States cntain at least ne cat r dg, and cats are nw slightly mre cmmn than dgs. 4 Further, up t ne third f individuals allergic t cats live in a hme with ne r mre cats. 5 Frm the Department f Pediatrics, Divisin f Allergy and Immunlgy, The Jhns Hpkins University Schl f Medicine. Supprted by Natinal Institutes f Health grants AI-77 and AI-3773, the Eudwd Fundatin fr Cnsumptives f Maryland, and GCRC grant n. 5M1 RR52. Received fr publicatin Feb. 8, 1995; revised Apr. 25, 1995; accepted fr publicatin June 2, Reprint requests: Rbert A. Wd, MD, CMSC 112, The Jhns Hpkins Hspital, 6 Nrth Wlfe St., Baltimre, MD Cpyright by Msby-Year Bk, Inc /96 $5. + 1/1/67512 Althugh the envirnmental distributin f cat allergen has been extensively studied, there is very little infrmatin abut the clinical relevance f specific allergen levels In hmes with cats, levels f Fel d 1 (Felis dmesticus allergen 1), the majr cat allergen, are typically very high and it has been assumed that these levels are capable f inducing symptms in mst patients wh are allergic t cats. In additin, cat allergen has been fund in settled dust samples frm hmes withut cats, as well as in every ther building where it has been sught, including newly built hmes, shpping malls, dctrs' ffices, and even hspitals. 9"14 Allergen levels in these sites are typically 1 t 1 times lwer than thse fund in hmes with cats, and the clinical significance f this lw-level expsure is cmpletely unknwn. Hwever, it has been shwn that many persns wh have never lived arund cats becme sensitized, implying that lw-level expsure may at least be capable f inducing sensitizatin. 15 In this study we measured airbrne Fel d 1, a ptentially mre useful marker f cat expsure than settled dust, in hmes bth with and withut 97

2 98 Bllinger et al. J ALLERGY CLIN IMMUNL APRIL 1996 cats. We then sught t relate these levels t thse seen during challenges in ur cat expsure facility and thereby assess the clinical relevance f envirnmental cat expsure, including the lw-level expsure encuntered in hmes withut cats. METHDS Hme sampling methds Hmes fr sampling were recruited by advertisement and wrd f muth. Settled dust samples were cllected by vacuuming a 1 m 2 area f carpeting r uphlstered furniture with a hand-held vacuum cleaner (Duglas Rx 365 Hand Vac, mdel N. 6735; Duglas Prducts, Walnut Ridge, Ariz.) fr 2 minutes. Filters were remved frm the vacuums and stred at -4 ~ C until prcessing. Air samples were btained with a small prtable pump (Gilian Instrument Crpratin, Wayne, N.J.) with flw rates f 3 t 4 L/min and a 25 mm rund glass fiber filter (Millipre Crp., Bedfrd, Mass.) cntained in a plastic cassette, which was attached t the subject's lapel. All pumps were calibrated befre each use with a Buck calibratr (A.P. Buck, rland, Fla.), and the flw rate and sampling time were recrded t calculate the vlume f air sampled. Subjects wre the pumps fr 1 hur during nrmal husehld activity, but they were asked t refrain frm vacuuming during the airbrne sample cllectin. In hmes with cats, subjects were als asked t refrain frm directly handling their cats during the sample cllectin. Filters were left in the cassettes and frzen at -4 ~ C until extractin. Baseline air samples were btained frm 37 hmes with cats and 4 hmes withut cats. Fr the hmes withut cats, 26 f the 4 had been ccupied by the same nn-cat wner fr at least 3 years, and nne f the hmes were knwn t have hused a cat within the previus year. Weekly air samples were als btained ver an 8-week perid in 12 cat-cntaining hmes, and weekly paired air and dust samples were cllected ver a 4-week perid in 12 hmes withut cats. Nine f the hmes withut cats, frm which weekly samples were btained, were selected because they had detectable airbrne Fel d 1 in their baseline samples, whereas the ther three were chsen at randm frm the baseline grup. Nne f the hmes sampled were ccupied by subjects studied in the cat challenge rm. Sample extractin and Fel d 1 assay The settled dust samples were remved frm the vacuum and weighed. They were then sieved thrugh a.3 mm brass mesh t prduce fine dust. The fine dust was weighed, and a 1 mg aliqut was extracted in 2 ml f brate-buffered saline, ph 8., by rtatin vernight. The extracts weie then centrifuged, and the supernatants were remved and stred at -2 ~ C. Samples yielding less than 1 mg f fine dust were extracted in a prprtinately smaller vlume f buffer. Filters fr airbrne samples were left in the cassettes and frzen at -4~ until extractin. Extractin was perfrmed by remving the supprt pads frm the cassettes (leaving the filter in place), adding 1.5 ml f piperazine-n, N'-bis [2-ethanesulfnic acid]-tween-8 t the cassette, and rtating the cassette vernight at 4 ~ C. Extracts were cllected by suctining the visible fluid frm the cassette and then cmpressing the filter in a 3 ml syringe t express any residual fluid. Return vlumes averaged 1.2 ml (range, 1. t 1.3 ml). Extracts were frzen at -2 ~ C until they were assayed. Fel d 1 was measured with a tw-site mnclnal ELISA, as previusly described. 16 The assay has a lwer limit f detectin f.4 ng/ml fr air samples, r 2 ng/m 3 fr typical sampling cnditins at a rate f 3 t 4 L/min fr 1 hur. Fr dust samples, the lwer limit f detectin is 5 ng f Fel d 1 per gram f dust. Cat challenge In an effrt t determine the clinical significance f airbrne Fel d 1 levels in hmes, cat challenges were perfrmed as part f anther study, at varying airbrne antigen cncentratins in ur cat rm facility. These challenges were perfrmed in a 13.7 m 3 rm cntaining tw cats, as described previusly, a7 The rm is furnished with a bed cvered with a sheet, an uphlstered chair, and a small carpet. The rm's ventilatin is fully adjustable. The cats are free t mve abut the rm except during challenges, when they are placed in a wire cage. The rm has been extensively characterized with regard t its ventilatin, air turnver, airbrne Fel d 1 levels, and airbrne Fel d 1 particle size distributin. 17 The rm has als been studied fr ther pertinent allergens, including dust mite and cckrach, and thse levels were undetectable. Vlunteer subjects wh were allergic t cats as determined by histry were recruited by advertisement and characterized by skin testing, end-pint titratin t cat allergen, RAST t cat allergen, and methachline challenge. Thse vlunteers with dcumented cat sensitivity were invited t underg a cat challenge, which invlved a 1-hur expsure in the cat rm. Medicatins were restricted befre challenge as fllws: antihistamines (72 hurs), inhaled [3-adrenergic agnists (4 hurs), ral [3-adrenergic agnists (shrt-acting, 6 hurs; lng-acting, 12 hurs), thephylline (12 hurs), nasal r inhaled crmlyn sdium (48 hurs), and nasal r inhaled Crticsterids (72 hurs). Immediately befre challenge, the cats were put in the cage, the rm ventilatin was turned ff, and the bedding was shaken t disturb allergen. Baseline spirmetry (mdel DECpc, spirmeter; Warren Cllins Inc., Braintree, Mass.) and peak flw recrdings (Mini-Wright peak flw meter; Clement Clarke Internatinal Ltd., Clumbus, hi) were perfrmed in an adjining rm befre subjects entered the cat rm. During the challenge, upper (cngestin, rhinrrhea, and pruritis) and lwer (chest tightness, wheezing) respiratry symptms were graded every 2 minutes n an arbitrary scale frm t 3, and all cughs

3 J ALLERGY CLIN IMMUNL Bllinger et al. 99 VLUME 97, NUMBER I e c s_,q s_ in 1- < 1 8 Hmes Hmes (n,,3) With Cats Withut Cats FIG. 1. Levels f airbrne Fel d 1 in 37 hmes with cats and 4 hmes withut cats. Dtted line dentes the lwer limit f detectin f the assay. The median level fr hmes with cats was 45.9 ng/m 3. Fr hmes withut cats with measurable Fel d 1, the median was 17 ng/m 3. and sneezes were cunted. Every 15 minutes, the subject exited t the adjining rm where spirmetry was repeated. At that time, the bedding was nce again shaken t maintain high airbrne allergen levels. After the challenge, peak expiratry flw rates and symptm scres were mnitred by the subject every 1 t 2 hurs fr 12 hurs. Challenges were stpped befre the 1-hur limit if the subject became t uncmfrtable r if FEVI fell by mre than 5%. Airbrne Fei d 1 levels were measured during challenges with the same persnal samplers used in hme sampling as described abve. Pump flw rates were calibrated befre each challenge, and the extractin and Fel d 1 assay prcedures were identical t thse used fr the hme samples. The prtcl was apprved by the institutinal review bard f the Jhns Hpkins University Schl f Medicine, and all subjects gave infrmed cnsent. Statistical analysis Spearman's crrelatin cefficient was used t cmpare paired air and dust samples. Nasal and pulmnary respnses in the high- and lw-level cat challenges were cmpared by using the Mann-Whitney U test. The variability f weekly hme samples was estimated by calculating the cefficient f variatin fr each hme after lg transfrmatin f the airbrne Fel d 1 data. RESULTS Baseline air samples were btained frm 37 hmes with cats and 4 hmes withut cats. As seen in Fig. 1, airbrne Fel d 1 levels were higher in hmes with cats than in hmes withut cats. Airbrne Fel d 1 was detectable in all 37 hmes with cats, ranging frm 1.8 t 578 ng/m 3, with a median f 45.9 ng/m 3. It was detectable in 1 f the 4 hmes withut cats, ranging frm 2.8 t 88.5 ng/m 3, with a median f 17 ng/m 3 (in the hmes with detectable allergen). T determine whether higher airbrne Fel d 1 levels in hmes withut cats culd be predicted by Fel d 1 levels in settled dust, dust samples were als btained frm the 4 hmes withut cats (Fig. 2). Settled dust Fel d 1 in these 4 hmes ranged frm belw detectin in tw hmes t 375 ng/gm f dust, with a median level f 258 ng/gm. Hmes with detectable airbrne Fel d 1 tended t have higher settled dust levels, althugh this crrelatin was nt statistically significant (r s =.19,p =.15). Further, there were tw hmes with very lw settled dust Fel d 1 levels (belw 1 ng/gm), which had detectable airbrne Fel d 1. T determine the variability f airbrne Fel d 1 cncentratins in hmes, weekly samples were btained ver an 8-week perid in 12 cat-cntaining hmes and ver a 4-week perid in 12 hmes withut cats (Fig. 3). Mst Fel d 1 levels in these hmes with cats fell within the range f 5 t 5 ng/m 3. The number f cats in each hme ranged frm 1 t 15, with a median f 2. Median levels f airbrne Fel d 1 crrelated significantly with the number f cats in the hme (rs =.77, p <.1). There was substantial week-t-week variability in airbrne Fel d 1 in all 12 hmes, althugh the variability in sme hmes was far greater than

4 91 Bllinger et al. J ALLERGY CLIN IMMUNL APRIL 1996 A 1" E ~1' c ~b I== =m < D (3]zzmm~ I I I l I Dust (ng/g) FIG. 2. Levels f Fel d 1 in paired air and dust samples cllected frm 4 hmes withut cats (r s =.17, p =.15). Dtted line dentes the lwer limit f detectin f the assay fr airbrne samples. A1 c, 1 L..Q k.. wm,< 1" e 8 ~ ~ g w g U 8 ~ 8 el...m.wmjq...r.w.wm..h.aml.n...w~...nn..mqn... i ()1'1 1'2 Hmes With Cats FIG. 3. Week-t-week variability f airbrne Fel d 1 in 12 hmes with cats sampled weekly ver an 8-week perid. Dtted line dentes the lwer limit f detectin f the assay. that in thers. Fr example, levels in hme n. 2 ranged frm belw detectin t 88 ng/m 3, whereas hmes n. 4 and n. 11 had generally high antigen levels and hme n. 8 had cnsistently lw antigen levels. Cefficients f variatin, calculated after lg-cnversin f these data, ranged frm 15% t 73%. Week-t-week variability f airbrne Fel d 1 was als determined in 12 hmes withut cats ver a 4-week sampling perid (Fig. 4). As nted, nine f these hmes were selected because they had measurable airbrne Fel d 1 in their baseline sample. Airbrne Fel d 1 levels in these hmes ranged frm belw detectin t 13 ng/m 3, r abut 1 times lwer than cat-cntaining hmes. All hmes had measurable Fel d 1 in at least ne f their weekly air samples. Five f the 12 hmes had detectable airbrne allergen in three f fur samples, and ne

5 J ALLERGY CLIN IMMUNL Bllinger et al. gll VLUME 97, NUMBER 4 ~ 1' C,Q 1' < 1 g 8 g 8...~ ~ ~ ~ Duet (.g/g) Hme== Withut Cats FIG. 4. Week-t-week variability f airbrne Fel d 1 in 12 hmes withut cats sampled weekly fr 4 weeks. Dtted/ine dentes the lwer limit f detectin f the assay. had detectable allergen in all fur samples. Cefficients f variatin f lg-cnverted values ranged frm 5% t 321%, which was substantially greater than thse bserved in the cat-cntaining hmes because f the smaller number f samples per hme and the larger number f nndetectable values. Weekly dust samples were als btained frm these hmes withut cats. Fel d 1 was detected in 47 f 48 samples, with cncentratins ranging frm 24 t 32,336 ng/gm. Median levels fr individual hmes ranged frm 4 t 1,4 ng/gm (Fig. 4). The ne hme with exceptinally high settled dust Fel d 1 levels was ccupied by an individual with extensive cat cntact utside the hme. It shuld be nted, hwever, that althugh this hme did have ne f the highest airbrne Fel d 1 levels (96 ng/m3), tw f its fur air samples had n detectable antigen. Cnversely, the hme with fur f fur psitive air samples (and the highest individual level) had very mdest settled dust levels, ranging frm 65 t 373 ng/gm. T assess the clinical relevance f hme airbrne Fel d 1 levels, we cmpared these levels t thse capable f causing symptms in ur cat challenge mdel. A ttal f 63 challenges were perfrmed and categrized as either high-level r lw-level, defined as an airbrne Fei d 1 level f greater than r less than 5 ng/m 3. The cutff f 5 ng/m 3 was chsen because levels belw that are mst cnsistent with thse encuntered in hme envirnments. There were 23 lw-level and 4 high-level challenges. Airbrne Fel d 1 levels in lw-level challenges ranged frm 13.1 t 448 ng/ m 3, with a median f 156 ng/m 3, whereas levels in high-level challenges ranged frm 622 t 31,381 ng/m 3, with a median f 1729 ng/m 3. Seven challenges were perfrmed at Fel d 1 levels less than 1 ng/m3; these have been identified in the figures because f their particular relevance t hmes withut cats. Upper respiratry symptm scres were averaged ver the 1-hur challenge t calculate a mean scre fr each subject. Median symptm scres were.8 fr the lw-level challenge grup and 1.2 fr the high-level grup (Fig. 5). Althugh there was a trend tward increased symptms at higher Fel d 1 levels, these differences were nt statistically significant (p =.1). In the seven challenges perfrmed at levels less than 1 ng/m 3, mean symptm scres ranged frm.1 t 1.2, with a median symptm scre equal t that f the entire lw-level grup (.8). Percent fall in FEV 1 was als cmpared between lw-level and high-level challenges (Fig. 6). The median percent decrease in FEV~ was 1% and 2.5% fr the lw-level and high-level challenges, respectively. These differences were significant, with a p value f.1. Ntably, in the seven challenges with a Fel d 1 level less 1 ng/m 3, the median FEV1 change was 15%, and three subjects had a fall in FEV~ f greater than 25%. The FEV]

6 912 Bllinger et al. J ALLERGY CLIN IMMUNL APRIL E # 1.5 & Q ee- c) c.5 g8 Z & Lw Level (N=23) ~:) High Level (N-4) FIG. 5. Mean upper respiratry symptms fr challenges perfrmed at lw levels f Fel d 1 (<5 ng/m 3) and high levels f Fel d 1 (>5 ng/m3). Slid circles represent challenges perfrmed at Fel d 1 levels less than 1 ng/m 3. changes in these subjects were 26%, 36%, and 39% at Fel d 1 levels f 72.3, 82.1, and 54.1 ng/m 3, respectively. DISCUSSIN Althugh a great deal is knwn abut the envirnmental distributin f cat allergen, remarkably little is knwn abut its clinical significance. Levels f Fel d 1 in settled dust, which may be capable f inducing sensitizatin r disease, have been prpsed but never substantiated. 18 ne area f particular cnfusin has been the lw level f allergen that is cmmnly fund in hmes and ther buildings that have never hused cats. In this study we have shwn that Fel d 1 can als be detected in the air f many hmes withut cats and that similar airbrne allergen levels are capable f causing significant symptms in sme patients allergic t cats. Several prir studies have dcumented the presence f cat allergen in hmes and buildings withut cats This allergen is presumed t be present because f passive transprt by individuals wh have been in cntact with cats. In sme hmes it may als be the result f prir cat habitatin, althugh in ur sample 7% f the hmes had been inhabited by the same persn (a nn-cat wner) fr at least 3 years. We have nw expanded n these previus studies, which fcused n allergen levels in settled dust, by bth measuring airbrne cat allergen and attempting t assess the clinical relevance f this lw-level cat allergen expsure. Similar t previus studies, we detected cat allergen in the settled dust f 38 f 4 hmes withut cats. Mre imprtantly, we were als able t measure Fel d 1 in baseline air samples in 1 f the 4 hmes and in at least ne sample frm all hmes in which repeat samples were btained. These levels were verall abut 1 times lwer than thse fund in hmes with cats, in which airbrne Fel d 1 was detectable in all 37 hmes. ther grups have been unsuccessful in finding measurable Fel d 1 in airbrne samples frm hmes withut cats. 11,14 This may be due t the sample size, because Sakaguchi et al. 11 nly studied seven hmes withut cats, and the number f nn-cat-cntaining hmes studied by Luczynska et al. 14 was nt specified. Settled dust samples were als btained frm the hmes withut cats t determine whether these samples, which are much easier t cllect and analyze, might help t identify hmes with higher airbrne allergen levels. Fel d 1 was present in the dust f all 4 hmes, and althugh airbrne Fel d 1 was mre likely t be detected in the hmes with higher settled dust levels, this relatinship was far frm cnsistent. In fact, tw hmes with settled dust levels belw 1 ng/gm had detectable airbrne allergen. When repeat samples were analyzed, we again fund that settled dust levels were nly rughly predictive f airbrne levels. It is

7 J ALLERGY CLIN IMMUNL Bllinger et al. 913 VLUME 97, NUMBER 4 therefre pssible t have significant airbrne Fel d 1 levels in the absence f a readily identifiable reservir, suggesting that settled dust samples must be interpreted with cautin in the assessment f actual cat expsure. The lack f crrelatin between air and dust Fel d 1 levels was als fund by Swansn et al. 13 This pr crrelatin again emphasizes the pr predictive value f dust samples. This variability culd be due t differences in ventilatin in the hmes r variability in the activities f the human beings r animals, leading t differences in antigen disturbance. We used ur cat challenge mdel t assess the ptential clinical significance f these hme airbrne allergen levels. Althugh this may nt be a perfect mdel f natural expsure, it has been shwn t clsely mimic hme envirnments in mst respects, including Fel d 1 particle size distributin. 17 We fund that bth upper and lwer respiratry reactins were mre likely t ccur at higher allergen levels, althugh these differences were less dramatic than ne might have expected. In fact, with regard t nasal symptms, we were unable t demnstrate a significant difference between high-level and lw-level challenges. Althugh a significant difference was fund fr FEV~ changes, several subjects in the lw-level challenge grup experienced substantial decreases in FEV 1, even at very lw airbrne antigen cncentratins. These results indicate that even the airbrne Fel d 1 fund in many hmes withut cats might induce symptms in certain highly sensitive individuals. Platts-Mills ~8 has suggested that Fel d 1 levels f 8 txg/gm f dust r greater in settled dust shuld be cnsidered a threshld level fr inducing bth sensitizatin and asthma and that settled dust levels less than 1 ~g/gm are nt clinically significant. In ur baseline samples nly three f the 4 hmes withut cats had a Fel d 1 level greater than 1 Ixg/gm, and nne had a level abve 8 Ixg/gm, and yet 1 f these hmes had detectable airbrne Fel d 1. In the 12 hmes withut cats, in which weekly samples were cllected, six f the 48 settled dust samples had a Fel d 1 level greater than 1 I~g/gm, and nly tw f 48 had a level abve 8 I~g/gm. f these, 29 f 48 air samples cntained detectable Fel d 1. Given the fact that many hmes had airbrne Fel d 1 levels capable f causing symptms, despite settled dust levels f less than 1 I~g/gm, these prpsed threshld levels need t be recnsidered. These findings are cnsistent with the fact that it is cmmn t find patients sensitive t cats wh m u. =: uj u cli Lw Level High Level (N=23) (N=4) FIG. 6. Percent fall in FEV1 fr challenges perfrmed at lw levels f Fel d 1 (<5 ng/m 3) and high levels f Fel d 1 (>5 ng/m3). Slid circles represent challenges perfrmed at Fel d 1 levels less than 1 ng/m 3. have never lived with a cat. In fact, ne study fund that skin test reactivity t cat allergen ccurred with equal frequency in children whether r nt they had ever lived with a cat. ~2 It is clear that the assessment f cat expsure, with regard t bth sensitizatin and disease, shuld nt be based slely n the presence r absence f a cat in the hme. Week-t-week variability f airbrne Fel d 1 was substantial in hmes bth with and withut cats. These results are similar t thse f Sakaguchi et al., H wh fund cefficients f variatin f 15.8% t 55.8% in cat-cntaining hmes, even thugh they used much lnger sampling times. It is likely that these fluctuatins are the result f varying degrees f disturbance n the part f bth the human beings and the cats in the hme. Such data are certainly cnsistent with anecdtal reprts frm patients, wh ften nte marked variability in symptms at different pints in time. Week-t-week variability was even mre prfund in the hmes withut cats. It was cmmn fr Fel d 1 t be undetectable during ne week and easily detectable during anther. This suggests that mre active disturbance may be required fr cat allergen t becme airbrne when the reservir is mre limited r that activity f the cats themselves is imprtant t the creatin f airbrne allergen. Cat activity was clearly shwn t be a cause f higher airbrne allergen levels in ur cat challenge rm. 17

8 914 Bllinger et al. J ALLERGY CLIN IMMUNL APRIL 1996 In cnclusin, we have shwn that Fel d 1 is measurable in air samples nt nly in hmes with cats, but als in hmes withut cats. In cat challenges acute upper and lwer respiratry reactins were induced in sensitized individuals with a brief expsure t cncentratins f airbrne antigen that were cmparable t thse fund in hmes, including hmes that d nt cntain cats. Any measurable airbrne Fel d 1 might therefre be clinically significant, and the ptential fr cat expsure shuld be cnsidered in all hmes. Thus althugh cat avidance shuld still be recmmended as the first line f treatment fr the patient allergic t cats, cmplete avidance is clearly nt pssible, and the need fr medicatins r immuntherapy must be carefully cnsidered. REFERENCES 1. Murray AB, Fergusn AC, Mrrisn BJ. The frequency and severity f cat allergy vs dg allergy in atpic children. J ALLERGY CLIN IMMUNL 1983;72: Gergen P J, Turkeltaub PC, Kvar MG. The prevalence f allergic skin test reactivity t eight cmmn aerallergens in the U,S. ppulatin: results frm the secnd Natinal Health and Nutritin Examinatin Survey. J ALLERGY CLIN IMMUNL 1987;8: Pllart SM, Chapman MD, Ficc GP, Rse G, Platts-Mills TAE. Epidemilgy f acute asthma: IgE antibdies t cmmn inhalant allergens as a risk factr fr emergency rm visits. J ALLERGY CLIN IMMUNL 1989;83: United States Bureau f the Census Statistical Abstract f the U.S. 114th ed. Lanham, Maryland: Bernan Press, 1994: De Blay F, Chapman MD, Platts-Mills TAE. Airbrne cat allergen (Fel d I). Am Rev Respir Dis 1991;143: Wd RA, Egglestn PA, Lind P, et al. Antigenic analysis f husehld dust samples. Am Rev Respir Dis 1988;137: Wd RA, Chapman MD, Adkinsn NF Jr, Egglestn PA, The effect f cat remval n allergen cntent in husehld dust samples. J ALLERGY CL1N IMMUNL 1989;83: Van der Brempt X, Charpin D, Haddi E, da Mata P, Vervlet D. Cat remval and Fel d I levels in mattresses. J ALLERGY CLIN IMMUNL 1991;87: Enberg RN, Shamie SM, McCullugh J, wnby DR. Ubiquitus presence f cat allergen in cat-flee buildings: a prbable dispersal frm human clthing. Ann Allergy 1993; 7: Munir AK, Einarssn R, Shu C, Drebrg SK. Allergens in schl dust. I. The amunt f the majr cat (Fel d I) and dg (Can f I) allergens in dust frm Swedish schls is high enugh t prbably cause perennial symptms in mst children with asthma wh are sensitized t cat and dg. J ALLERGY CLIN IMMUNL 1993;91: Sakaguchi M, Inuye S, Irie T, et al. Airbrne cat (Fel d I), dg (CanfI), and mite (Der I and Der II) allergen levels in the hmes f Japan. J ALLERGY CL[N IMMUNL 1993;92: Munir AKM, Einarssn R, Kjellman N-IM, Bjrksten B. Mite (Der p I, Der f I) and cat (Fel d I) allergens in the hmes f babies with a family histry f allergy. Allergy 1993;48: Swansn MC, Campbell AR, Klauck MJ, Reed CE. Crrelatins between levels f mite and cat allergens in settled and airbrne dust. J ALLERGY CLIN IMMUNL 1989;83: Luczynska CM, Yin L, Chapman MD, Platts-Mills TAE. Airbrne cncentratins and particle size distributin f allergen derived frm dmestic cats (Felis dmesticus). Am Rev Respir Dis 199;141: Linna. Envirnmental and scial influences n skin test results in children. Allergy 1983;38: Chapman MD, Alberse RC, Brwn MJ, Platts-Mills TAE. Mnclnal antibdies t the majr feline allergen Fel d I. II. Single step affinity purificatin f Fel d I, N terminal sequence analysis and develpment f a sensitive tw-site immunassay t assess Fel d I expsure. J Immunl 1988; 14: Wd RA, Laheri AN, Egglestn PA. The aerdynamic characteristics f cat allergen. Clin Exp Allergy 1993;23: Platts-Mills TAE, Allergens and asthma. Allergy Prc 199;11: