Measurement of Particle Sizes Associated with Airborne Viruses.

摘要

Health care personnel, swine and poultry farm workers, airline and public transportation workers, and others may be infected by a variety of viruses that can be transmitted through air. Conventional wisdom suggests that most transmission of infectious viruses occurs by droplet transmission although more recent research indicates that at least some viruses can be transmitted by the airborne route. This project assessed the sizes of particles with which viruses are associated in occupational environments. Methods were developed to quantify the amount of virus associated with airborne particles of different sizes and the viability of these viruses in the environment. The airborne particles were separated into different size ranges. We compared the eight-stage non-viable Andersen cascade impactor (ACI) and a micro-orifice uniform deposit impactor (MOUDI) and found that although both impactors were capable of size-selectively sampling viral aerosols, the ACI achieved higher relative recoveries than the MOUDI. The second step was to analyze the particles divided into each size range for the amount of virus present within them. The quantification of live viruses (avian influenza virus, swine influenza virus, avian metapneumovirus, human adenovirus type 1, and transmissible gastroenteritis virus) was accomplished by inoculation of appropriate cell culture systems. The bacteriophage MS-2 was quantified using its Escherichia coli host. Molecular methods such as polymerase chain reaction (PCR) and RT-PCR were also used as a semi-quantitative method to detect both live and inactivated viruses. We found that virus survival in air depended on both virus type and particle size. In general, virus survival was higher at large particle size (300-450 nm) than at 100-200 nm. Most of the published studies have used airborne viruses generated from artificial nebulizer suspensions. We conducted a study by aerosolizing MS-2 suspended in human saliva and found that actual human saliva was much less protective than cell culture media or artificial saliva. In another study, three different models of respirators were evaluated. Results suggest that the current NIOSH (photometer based) certification method is appropriate to prescreen respirators for infection control applications. An environmental chamber, which simulated a typical indoor environment, was then used to study viral aerosol survivability, transmission, and sampling. Aerosols of MS-2, human adenovirus type 1, and avian influenza virus were sampled size-selectively using a non-viable Andersen impactor. MS2 and AIV showed higher survival at lower temperature. Absolute humidity (AH) was found to be a better predictor of virus survival than RH, and the interaction between AH and temperature was not significant. In another study, susceptibility of aerosolized virus to ultra-violet germicidal irradiation (UVGI) was examined; all three viruses were significantly inactivated by UVGI. Due to damaged nucleic acid, most of the virus inactivated by UVGI could not be detected by either culture-based titration or by molecular methods. In summary, the results of this study has improved our understanding of virus behavior in air and will influence the procedures and technology used to prevent virus transmission in health care facilities, animal facilities, public venues, and other workplaces.