Dear Mr. Weinberg:
This letter is written in response to your request and expresses our professional opinion regarding physical and biological properties of the coronavirus, its infectious pathways, and possible methods to decrease the risk of infection in indoor environments. In March 2003, a novel coronavirus was discovered in association with cases of severe acute respiratory syndrome (SARS).
Both of undersigned (AZ and MK) were trained in virology, molecular biology and infectious diseases. Dr. A. Zakhartchouk has an extensive expertise in virology. He has published 19 peer-reviewed papers on various aspects of virology and is currently engaged in research on SARS vaccine development at the Vaccine and Infectious Disease Organization, University of Saskatchewan, Saskatoon (Canada). Dr. M. Khodoun has 7 years of experience in molecular diagnostic research and is currently employed at the Children’s Hospital Medical Center in Cincinnati (USA).
Coronavirus virions are spherical, enveloped virus particles, ranging from 80 to 160 nm in diameter. They may become airborne through the aerosolization of the body fluids and transmitted in the air while being carried by larger droplets (for example, with saliva aerosolized during cough and sneeze). Similar to the previously known coronaviruses, the newly-emerged SARS-associated coronavirus is also transmitted by droplet spread. The combination of a surface contamination and, possibly, an airborne spread may play a role. Recent data suggest that the virus may remain viable for considerable periods on a dry surface (up to 24 hours).
The discovery of a novel SARS-associated coronavirus provides a dramatic example of an emerging disease in humans caused by a coronavirus family. Although previously discovered and characterized human coronaviruses cause up to 30 percent of colds, they rarely cause a lower respiratory tract disease. In contrast, animal coronaviruses cause devastating epizootic of respiratory or enteric diseases in livestock and poultry. However, phylogenetic analyses and sequence comparisons showed that SARS-associated coronavirus is not closely related to any of the previously known coronaviruses.
Since the coronavirus, like many other viruses, can be transported in the air as aerosol particles, the risk of infection spread is proportional to their aerosol concentration. Depending on the ID50 and other factors, this risk can be drastically decreased if the viral particle concentration in indoor air is reduced. The use of indoor air cleaners and personal respirators is believed to be an adequate measure for the risk reduction.
We hope this information will be of your assistance.
Alexander Zakhartchouk, Ph.D., D.V.M. Research Scientist (II) Vaccine and Infectious Disease Organization, University of Saskatchewan
Marat Khodoun, Ph.D Research Fellow, Cincinnati Children's Hospital Medical Center, Research Foundation, Division of Developmental Biology
Prepared by Dr. Sergey A. Grinshpun, July 29, 2003
After the VI-3500* air purifier operates continuously for 15 min in a 25 m3 room, the concentration of submicron particles in this room decreases by a factor of 6. The overall protection factor of a surgical mask, enhanced by the ionic purifier, is about 30 (this takes into account the finding that the considerable improvement of the filter characteristics was partially suppressed by the leakage effect, see Phase 2 results). Thus, the number of submicron particles inhaled by a person is reduced by a factor of 6x30=180, instead of about 4, provided by a surgical mask alone. The air volume inhaled during a one-hour exposure is 1.8 m3 assuming that the breathing rate is 30 LPM. Some examples are presented below. The green color indicates that the estimated number of bioagent particles is below ID50; the red color indicates that the estimated number is above ID50.
*This document originally pertained to the VI-2500, Wein Products, Inc