Several readers have pointed me to an online piece on face masks and ultraviolet light as influenza control measures just published in the American Journal of Public Health. Both are presented as a Plan B in the (lkely) event Plan A’s vaccine and sufficient or sensitive antivirals are unavailable. The review by Weiss, Weiss Weiss and Weiss (I know a joke that goes like this, but this isn’t a joke) is measured an informative. First, face masks.
The authors point out that cloth surgical masks protect other people from you, not you from them. They discuss N95 and N100 respirators and provide interesting background on specifications and performance. The confusion as to the size of the infective particle in influenza transmission is reviewed, and the authors suggest that even large droplets may remain suspended for significant periods and travel longer distances than assumed, citing old literature and noting that newer literature is uninformative. The lack of data is startling. Whatever the data, no controlled studies exist on whether respirators can prevent influenza transmission, and serious questions exist on their feasibility in practical situations. They point out that without knowing the minimum infective dose for influenza we cannot know if even 98% aerosol protection is enough. The remaining 2% may be sufficient to infect.
There is also an informative discussion of leakage and fit testing:
Fit testing is time consuming, and in the health care setting, requires a technician. The test typically involves molding the mask until a seal is accomplished. Coffey et al found that most persons cannot be adequately fit tested to commercially available N-95 respirators.
Furthermore, it is uncertain if the utility of fit testing extends to beyond a single use. We could find no measurement of filtering efficacy with removal and immediate reapplication of the respirator, nor were we able to find any data to support the supposition that fit testing in 1 model of mask carries over into other masks of the same make and model. We also were unable to find assessments of efficacy after sustained use. The face is not a static surface; for example, motion of the jaw from swallowing, facial grimacing, or talking likely alters the seal. Even if all of these variables are negligible, there is still the effect of gravity pulling down on the mask. (Weiss et al., AJPH)
On the other hand, they suggest that using a cold cream or vaseline sealant might be a temporary workaround in an emergency, although its effectiveness and durability are unknown. It’s something to keep in mind. Their bottom line is equivocal: masks may be the only game in town and in that case, it’s a game worth playing:
Nonetheless, competent masks could prove vital in the control of a pandemic that overwhelms our health care system and paralyzes our cities. Availability of masks might allow some measure of confidence for essential services to continue. Masks have an indefinite shelf life and could be pivotal in responding to a potential bioengineered microbial event, such as smallpox and tularemia. Ensuring an adequate, readily available supply of masks is critical.
I’m not sure I agree, for various reasons, but I wanted you to see their opinion. They also make interesting comments about another technology I am more optimistic about, ultraviolet germicidal irradiation (UVGI). UV-C light is an effective germicide for influenza virus, although at that wavelength potentially dangerous to exposed skin and eyes. Systems that effectively irradiate the part of a room above the head work because there is usually a rapid and efficient exchange of air between the lower and upper portions of indoor environments. While this exchange is relatively rapid (around a minute), a good cough or sneeze can get to you before that, so this is not a panacea. But for environments with high exposure risks (patient rooms, emergency rooms, nursing homes, etc.), UVGI seems like an important and underutilized technology.
One of the readers who pointed me to the AJPH paper was the Marketing Manager for VIGILAIR Systems, Inc., a maker of UVGI units. He was quite honest and straightforward that he was engaged in shameless promotion of his company’s product and said he understood if I passed on writing about it. I almost did, but then decided that it fitted in with the rest of the post. Moreover much of what we read (and post on here) in the conventional press has been carefully placed there by marketing people much less honest than this reader. This is not to encourage anyone else to do this, but I thought it of sufficient interest to tell you about this. I’ve warned you about the source:
VIGILAIR Systems, Inc. announced the results of a study in which Ultraviolet Germicidal Irradiation (UVGI) was used to deactivate the Avian H5N1 virus, commonly referred to as the Bird Flu virus. This study was jointly funded by VIGILAIR Systems and a number of Wall Street based financial and insurance institutions that are concerned about the disruptive effects of a pandemic on business continuity.
Independent laboratory test results show that UVGI effectively deactivated the H5N1 virus. The study tested UVGI’s ability to deactivate the Vietnam strain of H5N1. This is the first time such testing has been performed on live H5N1 viruses, not surrogate microorganisms. (Vigilair Systems, press release)
The company is marketing it as a means to reduce hospital acquired infections and improve indoor air quality. There is some evidence for the former, not much for the latter as far as I know.
It’s another tool, one that seems more useful to me than mass stockpiling of masks. That’s an opinion, not fact. Your mileage might vary.