REYKJAVIK, ICELAND—Persons with cat allergy who are unwilling to remove the cat from the household can reduce their nasal symptoms by following environmental control (EC) measures aimed at reducing levels of Fel d 1.[1] However, stringent compliance with strict EC measures is required for symptom relief, the new study has found.

Unnur S. Björnsdottir, MD, one of the study investigators, said that these findings are “proof of principle” that a decrease in cat allergen—even with the cat in situ—produces a clinical effect on allergy symptoms. Dr. Björnsdottir acknowledged that compliance concerns make strict EC measures impractical for many patients because “only minute quantities of cat allergen are needed to cause significant symptoms once patients are sensitized.” Yet the protocol will still certainly benefit some.

Dr. Björnsdottir and colleagues from the National University Hospital in Reykjavik randomly assigned cat owners with confirmed cat allergy either to receive instruction in EC or to remain in an unchanged environment (UE). The 15 people in the EC group performed extensive allergen control measures beginning on the first day after randomization; interventions included washing all floors and furniture each week, washing the cat every two weeks, keeping the cat out of the bedroom, and sleeping with the bedroom windows open. No special form of ventilation (eg, HEPA filter) was used in any home. The 16 people in the UE group received no such instructions, though the cats were given a placebo “EC pill” once a week to suggest to the owners that an intervention was being made. In both groups, dust samples were obtained at defined times and then tested for Fel d 1 by enzyme-linked immunosorbent assay.

The EC measures functioned as intended. At each Fel d 1 reading after baseline, levels of the allergen were lower in the EC homes than in the UE homes; significant between-group differences were seen after two, three, and eight months. For example, among those using EC, Fel d 1 concentrations steadily declined from a baseline high of 39,440 ng/g to a low of 2,707 ng/g by eight months. In the UE, mean Fel d 1 levels remained constant, changing insubstantially from baseline (29,561 ng/g).

Dr. Björnsdottir said the initially higher baseline concentrations of Fel d 1 in the EC group, as well as their substantially worse allergy symptoms, could certainly have left more room for improvement in these subjects. However, after eight months, statistically significant improvements were seen in the EC group but not in the UE group. For example, nasal flow increased by 62 points in the EC group but decreased by 9 points in the UE group. Mean scores for congestion, rhinorrhea, and itching also markedly improved in the EC group only.

Compliance with the EC measures was, in the researchers’ words, “surprisingly” good. Major laxity was with cat washing every two weeks and keeping the cat out of the bedroom. (A post hoc assessment showed that compliance with both measures eventually ceased completely.)

The researchers noted that the observed benefits may in part be explained by the unintentional selection of a group of participants “hardy” enough to be able to comply with their challenging protocol. Only about 5% of the original volunteer cohort refused to participate after being informed of the study’s extensive requirements.

—Verna L. Schwartz, MS