Purpose of the Study
Air cleaners and air filtration devices have enjoyed considerable popularity as a form of environmental control to remedy allergic problems. There are, however, many unanswered questions in regard to their efficacy. This study attempts to address the question of efficacy of the high-efficiency particulate arrestor (HEPA) cleaners in reducing allergen levels and disease activity in the homes of cat-allergic patients who continue to live with the triggering allergen (cat).
This study involved adults who had asthma and/or allergic rhinitis. They all had a history of allergic symptoms with cat exposure to the extent they required daily medications. They also had at least one cat in the home.
A 1-month baseline period helped to determine the minimum amount of medication needed to control asthma and/or allergic rhinitis symptoms. Daily diaries were kept regarding medication use, peak flow, nasal and chest symptom scores, and sleep difficulty. At a home visit, the number of cats and the presence of carpeting was noted. Baseline air and dust samples were collected in the patient's bedroom. Pillows and mattresses were then covered and bedding was washed weekly. Patients were instructed to keep the cat(s) out of the bedroom. A second home visit was conducted to ensure compliance with the environmental control measures. For the next 3 months, a Honeywell Environcare HEPA filter was placed in the bedroom. This unit provided 15 air changes/hour in a 12- × 15-foot room. In the control group the filter was removed. Home visits occurred every month to sample the air and dust. A timer on the air filter units monitored compliance. Cat antigen, Fel d 1, was measured by enzyme-linked immunosorbent assay (ELISA). Other variables that were evaluated included spirometry, methacholine sensitivity, and radioallergosorbent test (RAST).
There were 35 patients in the study; 17 served as the control group. All study patients had cat-induced rhinitis and 28 had cat-induced asthma. Thirteen study patients had one cat and 18 had two. All but 1 patient had carpeting in the bedroom. There were no significant differences between the treatment and control groups in medication use or demographics. There was no change in the level of airborne Fel d 1 in either group during the baseline period when the cat was kept out of the bedroom and covers were in place. When the HEPA filter was added, there was a modest decrease over 3 months in the level of airborne Fel d 1 in the group with the active air filter. The geometric mean level decreased from 3.0 ng/m3 at baseline to 1.7 ng/m3 at 3 months. There was no difference in cat allergen levels in settled dust samples at any point during the study. There was a trend toward decreased nighttime nasal symptoms in the treatment group; however, this did not reach statistical significance. No significant differences were observed in chest symptoms, peak flow measures, sleep, medication use, spirometry, methacholine challenges, or RAST results.
The HEPA filter did provide for a significant decrease in Fel d 1 levels in the air. However, those using a HEPA filter did not experience any significant difference in any measure of disease activity for both rhinitis and asthma.
It must be noted that this paper does not deal with children at all; however, it does deal with a common problem that affects children. Parents see these forms of allergy treatment advertised and may ask their pediatricians about their efficacy. There are numerous options available for environmental control, many of which have not been studied in any rigorous way. This article points out a number of key concepts using this form of environmental control measure. Airborne levels do decrease, but the new level achieved was not associated with significant differences in disease control. The study emphasizes the importance of avoidance and the lack of efficacy of the HEPA units in this model of allergy.