Inactivation of Poxviruses by Upper-Room UVC Light in a Simulated Hospital Room Environment

Abstract

In the event of a smallpox outbreak due to bioterrorism, delays in vaccination programs may lead to significant secondary transmission. In the early phases of such an outbreak, transmission of smallpox will take place especially in locations where infected persons may congregate, such as hospital emergency rooms. Air disinfection using upper-room 254 nm (UVC) light can lower the airborne concentrations of infective viruses in the lower part of the room, and thereby control the spread of airborne infections among room occupants without exposing occupants to a significant amount of UVC. Using vaccinia virus aerosols as a surrogate for smallpox we report on the effectiveness of air disinfection, via upper-room UVC light, under simulated real world conditions including the effects of convection, mechanical mixing, temperature and relative humidity. In decay experiments, upper-room UVC fixtures used with mixing by a conventional ceiling fan produced decreases in airborne virus concentrations that would require additional ventilation of more than 87 air changes per hour. Under steady state conditions the effective air changes per hour associated with upper-room UVC ranged from 18 to 1000. The surprisingly high end of the observed range resulted from the extreme susceptibility of vaccinia virus to UVC at low relative humidity and use of 4 UVC fixtures in a small room with efficient air mixing. Increasing the number of UVC fixtures or mechanical ventilation rates resulted in greater fractional reduction in virus aerosol and UVC effectiveness was higher in winter compared to summer for each scenario tested. These data demonstrate that upper-room UVC has the potential to greatly reduce exposure to susceptible viral aerosols. The greater survival at baseline and greater UVC susceptibility of vaccinia under winter conditions suggest that while risk from an aerosol attack with smallpox would be greatest in winter, protective measures using UVC may also be most efficient at this time. These data may also be relevant to influenza, which also has improved aerosol survival at low RH and somewhat similar sensitivity to UVC.

Infection of phytoplankton by aerosolized marine viruses

“…This decay rate was detected under simulated atmospheric conditions of temperature15.9 ± 0.2°C, relative humidity 65-75%, and light intensity 700 μmol photons·m −2 ·s −1 provided by a halogen lamp with a spectrum simulating sunlight (400-700 nm) (SI Materials and Methods). This result is comparable to previous studies that reported nonmarine viruses can remain infective in the atmosphere for several hours (23)(24)(25)(26). In addition, the half-life of infectious EhV in the ocean under similar prevailing condition is, as expected, much longer, ∼35 h (13).…”

Aerosol Susceptibility of Influenza Virus to UV-C Light

“…For example, for a The Z values for influenza virus were statistically different as a function of RH. These differences showing that influenza aerosols are less susceptible to UV at higher RH than at lower RH have been noted in previous UV susceptibility studies for other organisms (18,19). In climate-controlled, indoor environments, high RH values near 75% may be unusual, but in areas without environmental controls UV effectiveness may decrease in the presence of elevated RH.…”

Primary biological aerosol particles in the atmosphere: a review

“…Even for the most stable viruses, k is typically of the order of 0.01 min (1 , corresponding to an effective half-life of about one hour (Donaldson, 1973;McDevitt et al, 2008). For most other viruses, the inactivation rate in aerosol is considerably higher (Harper, 1961;Miller et al, 1963;de Jong, 1965;Miller and Artenstein, 1967;Songer, 1967;Akers, 1969;Benbough, 1971;Barlow, 1972;Donaldson, 1972;Akers, 1973;Donaldson and Ferris, 1974).…”

“…Experimental data on the survival of viruses show that, on the whole, the inactivation rate becomes higher for all viruses with increasing temperature (Zhdanov and Gaudamovich, 1982a;Zhdanov and Gaudamovich, 1982b;Weber and Stilianakis, 2008). Also, the number of surviving viral particles in aerosol decreases with increased radiation dose that the virus aerosol is exposed to (Jensen, 1964;Zhdanov and Gaudamovich, 1982a;Zhdanov and Gaudamovich, 1982b;Sagripanti and Lytle, 2007;McDevitt et al, 2008). Relative humidity influences the survival of viruses in aerosol differently.…”