2002 Air Filter Study Raises More Questions Than It Answers about Benefits for Asthma

Vol. 16 •Issue 5 • Page 21
Asthma Care

2002 Air Filter Study Raises More Questions Than It Answers about Benefits for Asthma

Air filters cut asthma symptoms; more study needed.” Variations of that headline could be found in most of the major newspapers in December 2002. New services spread the article across the world. But before buying into the concept, it is important to look at what the study behind the story is really saying and how the data from that study have been received.

First, a look at the study itself. Canadian researchers from McMaster University, Hamilton, Ontario, published a review of 10 previously published randomized clinical trials that evaluated the effectiveness of air filtration systems on asthma symptoms.

Specifically, they tried to determine whether high-efficiency particulate air (HEPA) filters played a role in reducing allergy and asthma symptoms. The combined studies reviewed included some 216 adults and children with asthma. Participants were given either real or imitation air filtration systems for use in their homes and asked to keep a diary of their symptoms.

Based on the collective data from these diaries, the McMaster researchers concluded air filtration systems did “slightly” reduce reported allergy and asthma symptoms like wheezing and shortness of breath. The data did not show a correlation between the utilization of air filtration systems and an alteration (specifically a decrease) in medication usage.

The McMaster data perhaps raise more questions than they answer in clinical minds. Why, for example, did the individuals with the filter systems subjectively assess that their symptoms were better even though the clinical evidence failed to support this? Is it a psychosomatic response?


Study co-author and researcher Ellen Mc.Donald, RN, told a Reuters health reporter that by using air filters, “parents and children feel they have some control over their environment and their disease without medication.”

Is this the case? If so, the next logical question to ask is how much does the perception of “control” of one’s environment impact asthma sufferers’ symptoms overall? Is it the patient’s perception of control or the actual activity of the filter?

We do know that preventive measures such as adding mattress/pillow covers and removing dust collecting curtains and carpets have been shown to reduce symptoms. It is hypothesized these measures reduce the individual’s exposure to triggers by reducing the receptacle of them. Is there perhaps a degree of patient perception in these measures’ effectiveness as well?

Asthma guidelines have recommended the use of dust covers and the removal of carpets and the like for some time now, and some insurance companies have reimbursed for such measures.

Acceptance and possible payment of these measures by the insurance industry makes the air filtration data even more sticky. The researchers noted the majority of the studies they reviewed were supported by companies that manufacture air filtration systems. While drug companies have long been accepted as sponsors of clinical trials by professionals, the general public and certainly the managed care organizations are raising eyebrows at air filtration studies funded by air filter firms. In some respects, who can blame them.

Within hours of this study being published there were advertisements citing air filters as justification for an asthma therapy and going as far as claiming the filter systems are “the responsible way to protect your family against anthrax.” It appears possible the companies are trying to play on public fears in an uncertain world, but the conclusions do not seem to be built around valid peer-reviewed data.


It would be a financial windfall for the manufacturers and the distributors of air filtration systems if insurance companies did authorize and provide payment for air filter devices for the 14 million Americans diagnosed with asthma. Such marketing tactics make it less likely they will do so.

Researchers noted the filters reviewed in the study cost between $150 and $250 each. These are not unreasonable costs when compared to an emergency room visit or an inpatient hospitalization. But again questions arise. If a $250 system can reduce hospitalization usage by hypothetically speaking 15 percent, would a $3,500 system reduce them by perhaps 50 to 60 percent or more?

To date, there are no quantifying data to say yea or nay. From a patient’s perspective, however, more would seem to be better.

Managed care organizations are not going to agree to fund such devices without definitive data. And there are several points to consider on this track. Is it the particle size filtered that is important, for example? Or are the number of total room air filtrations per hour more important?

And if the insurance companies do authorize such filtration systems, do they treat the entire house? The patients’ primary rooms?

Do they make available permanent systems or portable ones? Or both? To their credit, the McMaster researchers recognized that more research and certainly more definitive studies need to be done. Specifically, the exact effects of air filtration’s systems on both subjective and objective symptoms will have to be defined.

Complex air filtration technology is not rocket science. It uses basic technology that any RCPs worth their salt can understand. So what is the final conclusion? That’s fairly easy to answer. Air filtration systems is a field of study that is wide open and easily within our reach as breathing specialists.

As the December headlines revealed, air filtration and its impact on asthma is a topic that will get good media attention. This looks like a prime opportunity for respiratory care as a profession to shine.


McDonald E, Cook D, Newman T, Griffith L, Cox G, Guyatt G. Effect of air filtration systems on asthma: a systematic review of randomized trials. Chest (2002 Nov; 122(5): 1535-42).

Margaret Clark is a Georgia practitioner.