Development of a Test System To Evaluate Procedures for Decontamination of Respirators Containing Viral Droplets

The aim of this study was to develop a test system to evaluate the effectiveness of procedures for decontamination of respirators contaminated with viral droplets. MS2 coliphage was used as a surrogate for pathogenic viruses. A viral droplet test system was constructed, and the size distribution of viral droplets loaded directly onto respirators was characterized using an aerodynamic particle sizer. The sizes ranged from 0.5 to 15 μm, and the sizes of the majority of the droplets were the range from 0.74 to 3.5 μm. The results also showed that the droplet test system generated similar droplet concentrations (particle counts) at different respirator locations. The test system was validated by studying the relative efficiencies of decontamination of sodium hypochlorite (bleach) and UV irradiation with droplets containing MS2 virus on filtering facepiece respirators. It was hypothesized that more potent decontamination treatments would result in corresponding larger decreases in the number of viable viruses recovered from the respirators. Sodium hypochlorite doses of 2.75 to 5.50 mg/liter with a 10-min decontamination period resulted in approximately 3- to 4-log reductions in the level of MS2 coliphage. When higher sodium hypochlorite doses (≥8.25 mg/liter) were used with the same contact time that was used for the dilute solutions containing 2.75 to 5.50 mg/liter, all MS2 was inactivated. For UV decontamination at a wavelength of 254 nm, an approximately 3-log reduction in the level of MS2 virus was achieved with dose of 4.32 J/cm² (3 h of contact time with a UV intensity of 0.4 mW/cm²), while with higher doses of UV irradiation (≥7.20 J/cm²; UV intensity, 0.4 mW/cm²; contact times, ≥5 h), all MS2 was inactivated. These findings may lead to development of a standard method to test decontamination of respirators challenged by viral droplets.During an infectious disease outbreak widespread panic can result from a limited understanding of the transmission route. Although some research points to a larger role for droplet nuclei (21, 28), other research suggests that droplets are the principal means of transmitting respiratory infections (10, 26). Droplets containing an infectious microorganism are believed to be transmitted to individuals who directly inhale the droplets resulting from coughing by carriers in close proximity or who ingest droplets spread to the mouth or the nose via the hands (7, 15). Large droplets were first defined as droplets more than 100 μm in diameter by Wells (30). Elsewhere, however, droplets more than 5 μm (23) or 10 μm (8) in diameter are often treated as large droplets. In this paper, the term “viral droplet” refers to all virus-containing liquid particles that retain their original size without significant evaporation, regardless of their specific size.N95 filtering facepiece respirators (FFRs) are routinely employed to prevent exposure of workers to biological hazards such as severe acute respiratory syndrome, tuberculosis, and novel H1N1 influenza A (6). In addition to CDC interim guidance (6), a recent report from the National Academies'' Institute of Medicine suggests that healthcare workers who are in close contact with individuals with novel H1N1 influenza illnesses should use fit-tested N95 respirators to reduce the risk of infection (18). This report also recommends increased research on influenza transmission and respiratory protection, which would enable policy makers to update these types of recommendations as additional disease prevention data become available.Current best practices suggest that once an FFR is worn in the presence of an infected patient, it should be considered potentially contaminated and discarded (5). However, during a pandemic outbreak a shortage of FFRs could occur (4). According to another report from the Institute of Medicine, during a 42-day influenza pandemic outbreak over 90 million N95 FFRs will be needed to protect workers in the healthcare sector (4). Furthermore, this report suggested that FFR reuse following decontamination should be considered a possible solution to deal with anticipated FFR shortages. Low-temperature biological decontamination methods have been suggested as a possible solution, but additional research needs to be done to determine whether infectious organisms can survive the decontamination process and if the decontamination method changes respirator fit (29).While it is well known that droplets play a role in the transmission of some respiratory infections, there is a lack of knowledge and data on the effectiveness of decontamination methods applied to respirators and porous personal protective equipment. There are several test methods for evaluation of the effectiveness of decontamination procedures for liquids and for hard porous or nonporous surfaces when they are challenged with viruses (2, 3, 27), while other methods are used to assess the effectiveness of decontamination procedures for FFRs when they are challenged with viral droplet nuclei (12). However, there is no test method to evaluate the effectiveness of biological decontamination procedures for disposable FFRs after they are challenged with viral droplets (liquid droplets containing a virus) whose sizes are similar to the sizes of droplets expelled by humans.Therefore, the aim of the present study was to develop a test system to evaluate the effectiveness of procedures for decontamination of respirators contaminated with viral droplets. The system was validated using two possible decontamination strategies: sodium hypochlorite and UV irradiation. It was hypothesized that the more potent decontamination treatments would result in corresponding larger decreases in the number of viable viruses recovered from the respirators than the less aggressive treatments.