New data enter ring in fit-testing debate
April 1, 2002 5 minutes read
New data enter ring in fit-testing debate
Makes less difference with better-fitting masks
When TB control experts and industrial hygiene whizzes debate whether to add annual fit-testing to the new health care worker infection-control guidelines, new data about N95 respirators’ inherent fitting qualities — or lack thereof — will likely play a role in the decision. The gist of the latest findings is that although fit-testing makes a big difference with respirators with inherently good fitting qualities, it doesn’t accomplish nearly as much with poorly fitting masks.
That’s hardly surprising when you think about it, says Greg Wagner, PhD, director of the Division of Respiratory Disease Studies at the Centers for Disease Control and Prevention’s National Institute of Occupational Safety and Health (NIOSH). "It’s almost self-evident that with the masks that fit fewer people, there will be more benefit from fit-testing," he says.
Still, Wagner cautions that it’s too soon to speculate how those new findings will play into the new guidelines. "We’re still at the point where we’re validating the data and trying to understand its implications," he says. "We definitely feel it’s important research."
One suggestion that’s reportedly come up at meetings where the new guidelines are being hashed out has been to let hospitals off the hook, provided they invest in respirators with better fitting qualities (and after at least an initial fit-test, aimed at weeding out the small percentage of workers who don’t fit even a highly "fittable" mask).
Reinforcing good donning procedures
The solution may not be that straightforward, though, say Wagner and others. For one thing, it can be argued that annual fit-testing has the effect of reinforcing proper donning procedures; that is, if a wearer isn’t going through the motions correctly every day, it doesn’t matter how good a mask she’s using.
The good news for mask-shoppers, at least, is that results are in from a new NIOSH study of respirators now on the market. The top three performers in the study were the 3M 8110-s and the 3M 8210 (which is the first model’s medium and large version); the 3M 1860, along with its smaller cousin, the 3M 1860-s; and the Affinity Ultra MSA. The study comes from the lab of Chris Coffey, PhD, a senior research chemist at the laboratory research branch of Wagner’s division. It succeeds a previous study, the results of which were published in the Dec. 11, 1998, Morbidity and Mortality Weekly Report. (Coffey and others contacted at NIOSH for this story made it plain that the agency does not recommend one brand of mask over another.)
But even with Coffey’s new findings in hand, mask-buyers need to be wary. Even though two of the top performers in the Coffey study come from 3M, another 3M model scored near the bottom of the heap in the study, says Paul Jensen, PhD, chief of the laboratory research branch. "The moral here is that performance is clearly model-specific, not company-specific," Jensen notes. Models (and hence fitting traits) can also change from year to year as manufacturers try to shave a half-penny or so off the cost, says Coffey.
Taller, heavier, more Asian work force
Another proviso regarding the findings is that the prototype facial structures for the test panel Coffey used date back to 1967-1968. Since those far-off years, there have been changes, among them an influx of Asians into the health care work force, with their characteristically smaller faces and nose bridges. All sectors of the work place have also seen workers grow heavier and taller, Coffey adds.
Still, the panel’s findings are far from invalid, Coffey adds. The existing panel (which is currently being updated to match today’s workers) "still covers a large portion of the American work force," Coffey claims. "The main differences are probably in the extremes." For example, the smallest Caucasian face is still bigger than the smallest Asian face.
More new data from Coffey’s lab underscore the flaws inherent in subjective fit-testing. Subjective, or qualitative, fit-testing relies on determining whether a subject wearing a mask and placed under a hood can recognize a bitter or sweet test agent introduced into the hood. Compared to quantitative fit-testing (which is done with a pricey gizmo called a Portacount, which must be fitted with an equally costly adapter), Coffey has found that qualitative fit-testing misses the mark in two directions.
More bad news on subjective fit tests
First, the subjective tests produce about 40% false negatives. Second, the subjective tests yield about 9% false-positive results, saying people have gotten a good fit when actually they have not. Obviously, the second group gives the most cause for concern, adds Coffey.
Where the argument over annual fit-testing grows really murky is when experts begin to debate levels of protection and whether half-mask filtering facepiece respirators really provide the protection it’s assumed they do compared to their predecessors, the elastomeric masks. Add to that debate (which NIOSH is working to resolve with a two-year study that’s about halfway completed) the related issue about whether health care workers even need the level of protection the agency says they do.
How many microbes are too many?
"A real challenge with this field is that we simply don’t know what level of protection is essential," concedes Wagner. "Unlike industrial settings, where you can measure particles and predict their effects, we simply don’t know how many microbes are too many,’ or how infectious a given patient may be, or how susceptible the host is."
To Pat Parrott, RN, infection control coordinator at the Infection Disease Clinic in Atlanta, the answer to that question is plain. "I’ve been a TB controller since 1992," Parrott says. "Does my mask fit perfectly 100% of the time without a leak? No. But after all these years of working with TB patients, I’m still PPD-negative." Health care workers wearing a mask don’t convert, she adds, not because the mask is always a perfect fit, but because when someone is wearing a mask, the patient lying in the bed is known to have TB, so that environmental and administration precautions are in force.
Wagner agrees. "Respiratory protection has an important role to play, but it will always be last in the hierarchy of controls," he says.
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