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Are you aware of any literature/data to support a patient who is cat allergic and purchasing a home that currently has two cats in it needing to replace duct work in the home? We discussed that it will likely take four months of vigorous cleaning (removing carpet, painting, drapery) to rid the home of the cat dander, but she specifically asked about the duct work before purchasing this home.


I am not aware of any data related to duct cleaning and indoor allergen exposure. Part of the problem is the type of duct work varies and the possibility of retaining allergen would also vary. Domestic exposure within the building is much more likely to be important than the potential allergen on the heating and ventilation duct work. The cat allergen in particular is a very small particle and would not likely impact on the duct work material with residual time sufficient for adherence. If I were to make any recommendations, and in this case I do not think I would make any additional environmental control measures, you may wish to consider having a high efficiency particle filter installed. This could possibly mitigate cat sources within the entire home and not just the duct work. However, there is precious little data supporting such filtration devices (see Ask the Expert question below).

In summary, I would not recommend duct work cleaning or other heating/ventilation mitigation but focus on domestic cleaning, particularly carpet.

5/9/2015: Air filtration choices
I am a physician medical writer now called upon to create content in multiple allergy-related topics for a lay audience. One topic focuses on choosing the best allergen filtration method. I have two rated questions (without asking for specific product endorsements):

- Does AAAI recommend any method of in-room filtration? HEPA or non-HEPA based?
- Any recommendations for filters in window ac units?

There is no definite evidence of filtration clinically benefiting patients with allergic disease, but this may be the result of the studies being of insufficient durations to prove benefit. The best review of the topic is by Sublett et al in 2010, a report of the Indoor Allergen Committee of the American Academy of Allergy Asthma and Immunology. This paper is well referenced and I do not think anything has changed since publication. One of the challenges is that the size of various allergens found inside vary, making the optimal filter possibly differing among allergens. HEPA filtration, devices that capture particles 0.3 micron and greater, are considered necessary for animal allergens and mold spores. Pollen is much more easily captured, although the possibility of pollen fragments could provide a source of pollen allergens in smaller particles.

In summary, the AAAAI does not recommend any specific method of in-room filtration for in-room or window air conditioners. The choice will depend on the type of allergy and a variety of features of the living space, which would make designating a specific device or filter type challenging. The following quote from the reference summarizes the state of the art:

“As far as optimal choice of cleaning devices, initial cost and ease of regular maintenance should be considered. Portable room air cleaners with HEPA filters, especially those that filter the breathing zone during sleep, appear to be beneficial. For the millions of households with forced air HVAC systems, regular maintenance schedules and the use of high-efficiency disposable filters appear to be the best choices. However, further studies and research in this area are desirable to make more definitive recommendations in the role of air filtration on improving disease outcomes.”

Sublett JL et al. Air filters and air cleaners: rostrum by the American academy of Allergy, Asthma & Immunology Indoor Allergen Committee. J Allergy Clin Immunol 2010;125:32-38.

I hope this information is of some assistance.

All my best.
Dennis K. Ledford, MD, FAAAAI

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