Are Powered Air Purifying Respirators a Solution for Protecting Healthcare Workers from Emerging Aerosol-Transmissible Diseases?

For the third time in less than 20 years there is global concern about a novel coronavirus causing significant respiratory morbidity and mortality. The first cases of Severe Acute Respiratory Syndrome (SARS) were reported by China to the World Health Organization (WHO) in 2003; one-third of these were among healthcare workers (WHO, 2003). By the end of the outbreak in 2004, more than half (378; 57%) of the 667 SARS cases treated in Asian and Canadian outbreak hospitals were healthcare workers or medical students (Sepkowitz and Eisenberg, 2005). At the time of and for many years after the SARS outbreak, there was much consternation among the medical and infectious disease communities about the organism’s mode(s) of transmission. Aerosols (both fine particles and larger droplets) had to be at least partially responsible for the relative ease with which SARS was transmitted from person to person. As more detailed epidemiologic data were published, this proved to be the case—risk factors for nosocomial transmission of SARS included exposure during aerosol-generating medical procedures, failure to isolate infectious patients, and the lack or uneven use of personal protective equipment (Scales et al., 2003; Fowler et al., 2004; Ofner-Agostini et al., 2006; Chen et al., 2009). In May 2014, when the first cases of Middle Eastern Respiratory Syndrome (MERS) were reported in the USA 2 years after initial outbreaks in Saudi Arabia, Dr Rachael Jones and I published a Commentary on the Center for Infectious Disease Research and Practice website (Brosseau and Jones, 2014). We argued that MERS was likely an aerosol-transmissible disease, because it resulted in symptoms similar to SARS (cough, diarrhea, and vomiting) and patients would likely undergo aerosol-generating procedures, such as intubation and bronchoscopy. As with SARS, early data suggested aerosol transmission of MERS among hospital patients located at some distance from each other. As with SARS, the MERS coronavirus remains viable as an aerosol and on surfaces for long periods of time at low relative humidity. We argued that healthcare workers should be provided with fit-tested N95 filtering facepiece respirators (FFRs), at a minimum, when caring for MERS patients. For exposures to high concentrations of infectious particles, such as from patients experiencing severe symptoms or during aerosol-generating procedures, we recommended that healthcare workers should be wearing powered air purifying respirators (PAPRs), which offer a higher degree of protection than FFRs. At the time of our Commentary, the Centers for Disease Control and Prevention (CDC) was recommending contact, droplet, and airborne precautions for MERS; WHO was recommending only contact and droplet precautions. The WHO guidance for MERS, updated in October 2019, now recommends respirators and well-ventilated negative pressure rooms for aerosol-generating procedures (WHO, 2019). While this is a small step forward, the WHO guidance continues to recommend surgical masks for healthcare workers when caring for hospitalized MERS patients. What does this mean for the current coronavirus outbreak of COVID-19? There are some similarities in symptoms with SARS and MERS, in particular cough, that suggest there is some possibility for aerosol transmission. Reminiscent of SARS and MERS, a Chinese physician—who tried early on to warn colleagues of a new disease—has died from infection with COVID-19. There is evidence of person-to-person transmission from patients to family members, close contacts and healthcare workers, which suggests the organism is capable of remaining viable in the air or on surfaces for some period of time. For COVID-19, WHO is recommending only standard and droplet precautions for patient care, with isolation of patients if possible (WHO, 2020). They recommend respirators (N95 FFRs) only for aerosol-generating procedures; otherwise, medical (surgical) masks are considered to be appropriate personal protective equipment for healthcare workers. The latter recommendation is typical of WHO while the former is a major step forward for an organization that has generally failed to recognize the importance of aerosols and respirators during past infectious disease outbreaks. On the other hand, CDC recommends that patients be cared for in airborne isolation rooms following standard, contact and airborne precautions to include eye protection. Healthcare workers should wear respiratory protection—at a minimum an N95 FFR. CDC cautions against the use of aerosol-generating procedures, which should only be performed in an airborne isolation room with a limited number of healthcare workers—wearing at least an N95 FFR—present (CDC, 2020). These recommendations are a big improvement over the initial CDC guidance for SARS, although it would be more appropriate to recommend the use of a respirator with a higher level of protection—such as a PAPR—for exposures to patients with serious symptoms or undergoing aerosol-generating procedures. The article in this journal by Dr Chugtai et al. describes a tight-fitting PAPR with a design that differs significantly from those currently on the market. Developed originally for mining operations, at first glance the CleanSpace2 PAPR looks like a half-facepiece elastomeric respirator; rather than a belt-mounted battery and hose apparatus, the battery and filter are located at the back of the neck. While the healthcare providers interviewed in this study appear to have limited experience and training with PAPRs, their reactions are generally positive. Others have found similar results with healthcare workers asked to assess the comfort and ease of use of more traditional PAPR models (Khoo et al., 2005), although one investigator found difficulties in communication, especially in noisier ICU environments (Radonovich et al., 2009). PAPRs have enjoyed success in some healthcare facilities (Wizner et al., 2016). They offer some important advantages over other types of respirators, being cooler and more comfortable to wear for long periods of time. Loose fitting PAPRs (e.g. with hoods) do not require fit testing, a popular feature for men not wanting to shave. PAPRs are a good choice for exposures to high concentrations of infectious aerosols, particularly when risks are unknown or uncertain. A fit-tested tight-fitting half-facepiece PAPR has a protection factor of 50 vs. 10 for a negative pressure half-mask respirator (filtering facepiece or elastomeric). A 2015 Institute of Medicine workshop on the use and effectiveness of PAPRs in healthcare raised some important issues that need to be addressed before such respirators will be more fully adopted (IOM, 2015). These include the need for designs that protect patients as well as wearers, especially during surgical and similar medical procedures; more options for visibility and communication with patients; methods for assessing correct donning and doffing; the ability to adjust air flow; and lower costs. Incorporating PAPRs into a respirator program requires additional procedures and manpower for managing batteries, maintaining and replacing multiple parts, and proper storage, cleaning, and training. Despite these barriers, there is a place for PAPRs in healthcare settings, especially for exposures to well-known or emerging diseases with the potential for infection via the aerosol route. The precautionary approach suggests we should be offering respirators with higher protection factors, such as PAPRs, when such exposures are likely in healthcare settings.