Clinical effects of air ®lters in homes of asthmatic adults sensitized and exposed to pet allergens H.Francis,G.Fletcher,C.Anthony,C.Pickering,L.Oldham,E.Hadley,A.CustovicandR.Niven North West Lung Research Centre, Wythenshawe Hospital, Manchester, UK Summary Background Despitemedicaladvice,manypet-allergicasthmasufferersrefusetoremovethepetto whichtheyaresensitizedfromtheirhome. Objective We aimed to assess the clinical effects of air cleaners in the homes of adult asthma patientssensitizedandexposedtocatsand/ordogs. Methods We performed a randomized, parallel-group study of 30 asthmatic adults sensitized to and sharing a home with cats or dogs. The effects of placing air cleaners in the living room and bedroomfor12monthsandusinghighefficiencyparticulateairfiltervacuumcleaners(activegroup) were compared with using these vacuum cleaners alone (control group). Measures of airway responsiveness, treatment requirement, lung function, peak flow, reservoir and airborne allergen were recorded before, during and after the interventions. A beneficial clinical response was as- sessed in terms of a `combined asthma outcome'. This was defined as a two or more doubling dose improvement in bronchial hyper-reactivity to histamine and/or a reduction in treatment requirement of at least one step change on the British Thoracic Society guidelines for asthma treatment. Results Abeneficialclinicalresponsewasobservedin10/15subjectsintheactivegroupcompared with 3/15 in the control group after 12months intervention (P  0.01). No significant differences between the active and control groups were detected for changes in measures of lung function, reservoirpetallergenandairbornepetallergenduringthestudy. Conclusion Whilst the study design has not allowed complete exclusion of a placebo effect, we believethatthispragmaticstudyofadultasthmaticpatientssensitizedandexposedtopetsresultedin asmall,butsignificantimprovementincombinedasthmaoutcome. Keywords adults, air cleaner, allergen avoidance, allergens, asthma, bronchial hyper- responsiveness,HEPA,lungfunction,pets Submitted 29 April 2002; revised 21 September 2002; accepted 7 October 2002 Introduction Catsanddogsarethemostpopularpetsinthewesternworld anduptoathirdofasthmasuffererssharetheirhomewithapet [1]. Sensitization to cat allergen has been shown to be a risk factor for patients seeking treatment in emergency rooms [2]. Despitecontinuedsymptomsmanycat-ordog-allergicpatients considerremovaloftheanimaltobeanunacceptableoption[3]. Airbornecatanddogallergencanbedetectedinundisturbed conditionsforprolongedperiods[4±7],whereashousedustmite allergenonlybecomesairborneaftervigorousdisturbanceand settles rapidly [7±9]. Pet allergens are carried on smaller par- ticlesthanhousedustmiteallergen[7].Thisislikelytounderlie therapidonsetofsymptomsexperiencedbycat-ordog-allergic patientsenteringahousewithapet[4,6]. High-ef®ciency particulate air (HEPA) cleaners have been shown to effectively remove pet allergen from the air [5,10,11];however,thesedeviceswereshowntobeineffective in improving asthma control in dust mite-sensitized individ- uals [10,12]. HEPA vacuum cleaners have been shown to reduce reservoirs of pet allergen [13,14], without leaking allergen[15]. Where removal of the pet is not an option, alternative methods of reducing allergen loads are necessary. Very few studieshaveassessedtheclinicaleffectsofavoidancemeasures inpet-allergicpatients.Arecentstudyinvestigatingtheuseof aircleanersinthehomesofchildrensensitizedandexposedto pet allergen demonstrated improvements in bronchial hyper- reactivity[16].However,asimilarstudyofadultswithasthma and/orallergicrhinitisdidnotdetectanysigni®canteffectofair cleanersonclinicalmeasures[17].Theaimofthisstudywasto assess the effect of using air cleaners in addition to HEPA Correspondence: Helen Francis, North West Lung Research Centre, Wythenshawe Hospital, Southmoor Road, Manchester M23 9LT, UK. E-mail:hfrancis@fs1.with.man.ac.uk ClinExpAllergy2003; 33:101±105 ß 2003 Blackwell Publishing Ltd 101