Demystifying theoretical concerns involving respirators with exhalation valves during COVID-19 pandemic

The global COVID-19 pandemic continues to create unprecedented demands for respiratory protection for health care personnel (HCP). This demand has forced HCP to utilize respirators they might not normally use in an effort to protect themselves including those models of N95 filtering facepiece respirators and almost all models of reusable (elastomeric) respirators that include exhalation valves. These respirators provide HCP with quality respiratory protection. Recently, the Centers for Disease Control and Prevention (CDC) have published recommendations that respirators with exhalation valves not be used for source control; the theoretical concern would be HCP wearing a valved respirator who has an asymptomatic infection with SARS-CoV-2 might transmit this virus.² We offer the following viewpoint and suggested strategies to address this theoretical concern. Respirators with exhalation valves remain an important element of personal protective equipment for HCP to use during response to this pandemic and prior. Comprehensive evaluation has found these respirators an effective and a viable option to disposable N95 respirators.³ At times crisis interventions have been needed wherein HCP have had to rely on procedure or surgical masks because N95 respirators were not available. Further, elastomeric respirators are generally sturdier, can be disinfected with surface disinfectants and the filter media are effective for weeks to months based on manufacturer instructions for use.

While CDC's recommendation above only speaks to N95 respirators with valves, HCP have asked if this guidance extends to elastomeric respirators. Further CDC recommends if a valved respirator is used and source control is needed, to cover the exhalation valve with a surgical mask, procedure mask, or a cloth face covering – really? One wonders how effective a seal you can get with a surgical mask much less a bandana or neck gaiter draped over an exhalation valve. Still, covering an exhalation valve is a better alternative than the one proposed by the media in follow-up to the CDC recommendation. An article from the Washington Post declares: “Face masks with valves or vents do not prevent spread of the coronavirus, CDC says.”⁸ The article asserts that “the Centers for Disease Control and Prevention warned against wearing masks with exhalation valves,” and “Masks with valves have been banned by major US airlines...,” and concludes with the CDC recommends simple cloth facemasks instead. A similar headline from NBC News states: “CDC: Avoid exhalation valve masks to stop the spread of COVID-19.”⁶

We have not been able to identify any peer-reviewed studies to support the recommendation to ban masks or respirators with exhalation valves. Instead, there are media interpretations of what the CDC intended to say, and there is now doubt of the benefit of not only simple facemasks with exhalation valves but also elastomeric air purifying respirators and N95 respirators with valves. It must be remembered that there are 2 requirements that need to be recognized, understood and balanced – protection of HCP and protection of patients and others in the hospital or health care facility. Respirators without exhalation valves do both, respirators with exhalation valves protect the HCP and their presence may increase the risk to the patient. The significance of this risk has not been evaluated and we as the authors of this commentary are concerned that N95s with exhalation valves and elastomeric air purifying respirators might be thrown out as the baby with the bathwater. Unintended consequences like eliminating respiratory protection options that are effective and expands the range of devices should there be shortages of certain models without exhalation valves may occur.

So what is the risk?

Drawing an analogy between use of a respirator with an exhalation valve, and use of a powered air-purifying respirator, both have unfiltered exhaust valves or ports. In vitro evidence involving use of a powered air-purifying respirator in an operating room did not find the device added any appreciable level of contamination to the surgical site.⁵ A recent article in Science Advances⁴ measured expelled droplets during speech while wearing facemasks including an N95 with and without an exhalation valve. The relative droplet count of the N95 respirator with and without an exhalation valve is presented along with the other masks. The relative droplet count of the N95 with an exhalation valve approximates that of other cloth mask options; it did not appear to be extremely high but the risk still needs to be evaluated. There are reportedly studies underway to describe and quantify the risk from an exhaust valve in an air-purifying respirator. However, to date, there are no peer reviewed studies supporting or proscribing use of a respirator with an exhaust valve.^{3 , 7} There also has been no documented evidence of spread of COVID-19 from an air-purifying respirator with an exhaust valve that the authors are aware of.

Improvements in practice, such as universal face covering by all who enter a health care facility is recommended by CDC and there is evidence this strategy lessens risk of occupational exposure and transmission to HCP.⁹ CDC has also recently recommended HCP wear eye protection during direct care of all patients – not solely those who are persons under investigation for or confirmed to be infected with SARS-CoV-2.² Recent investigation of universal addition of eye protection among community HCPs have also found this prevents exposure.¹ On balance, these additional containment tactics significantly mitigate the theoretical risk of release of SARS-CoV-2 from HCP wearing a valved respirator. The calculation of this probability also seems extremely remote as prevalence of infection among HCP is low, duration of infection is time limited, for example, no more than 14 days, most virus release during a sneeze or cough while wearing a valved respirator is contained and both procedure and surgical masks still release exhalation around the sides and top.

Recommendations

Do we need to use caution with respirators with exhaust valves? Yes. There remain many unknowns with SARS CoV2 and work that needs to be done on: what steps minimize the wearer as a source of SARS COV2, how much virus is shed by an asymptomatic wearer, method of propagation – airborne versus large droplet contact, what is the infectious dose and in the case of masks and respirators with exhalation valves, what is the role of valve in wearer comfort, user acceptance and perhaps increased use of the mask? Should we eliminate respirators with exhaust valves from the armamentarium? No, not unless there is a better solution.

When respirators with valve are worn source control, if needed – for example, HCP caring for a patient who is not suspected of SARS-CoV-2 or recently tested negative – can be accomplished by wearing a face shield over the respirator or, if tolerable, a disposable, procedure mask.

If there is one lesson that can be learned from the pandemic, it is the need for evidence-based practice where decisions are based on scientific and epidemiological studies. We should be careful that we do not rush to judgement based on perceptions of risk.