University of Cincinnati Medical Center
Department of Environmental Health University of Cincinnati
Mr. Stanley Weinberg Wein Products Inc.
Dear Mr. Weinberg,
You have requested a letter expressing my opinion as to whether the findings on the efficiency of your ion generating equipment, which has been tested in our laboratory, can be extrapolated to the SARS virus, the Anthrax bacterial spores, and the Smallpox virus. As I understand it, your request relates to two issues: (1) whether the aerosol concentration decrease observed in our tests with non-pathogenic particles is expected to occur with the above biological agents and (2) if so, would your air purifying equipment provide any meaningful degree of protection against airborne microorganisms causing SARS, Anthrax, or Smallpox.
With respect to the first question, it is my opinion that the aerosol concentration reduction, which we found earlier for test particles ranging from about 0.3 to 3 microns, can be extrapolated to any particles of this aerodynamic size range, regardless of their infectious characteristics.
Furthermore, our recent preliminary study has shown that the above particle size range may be extended to lower sizes: below 0.04 µm (as measured by the ELPI). Thus, the entire tested particle size range covers the sizes of most airborne viruses and bacteria.
The next question relates to the evaluation of the protection efficiency against SARS and other diseases for which the airborne transmission has either been identified or anticipated. It is presently anticipated that the SARS-causing virus can potentially be transmitted via airborne routes, i.e. with the droplets from a human sneeze or cough. Generally, the sizes of single viruses range from about 0.04 to 0.3 µm. Aerosolized saliva droplets containing viruses may be one or two orders of magnitude greater. However, as some water content of these droplets evaporates rapidly, most of the virus-carrying particles fall into the size range of about 0.1 to 3 µm. This range has been tested in our experiments. Our data show that your ion generating equipment,
including the tested Vortex VI-3500* (stationary) and Minimate™ AS180i* (wearable), should significantly reduce the concentration of droplets of 0.1 to 3 µm in the vicinity of the ionic air purifiers (at least, under the conditions tested of our laboratory). This reduction in the aerosol concentration should occur in the breathing zone of a person using your wearable ionic purifier and in a room in which your stationary unit is operating. The effect was found to be time-dependent and indoor air volume- dependent. The aerosol concentration reduction is especially pronounced in confined spaces and may vary considerably from one model/manufacturer to another, depending on the ion emission rate and other factors.
It should be understood that ionic air purifiers are not generally viewed as a way to replace personal masks or respirator filters. However, under certain conditions, the utilization of ionic devices may offer the same or comparable air purification efficiency as achievable with surgical masks and respirators while providing a greater comfort level for the wearer/user. It should be also understood that no claims must be made that your ionic air purifiers can fully eliminate the risk of inhaling airborne particles or prevent the transmission of infectious agents in indoor air. The reductions in airborne particle concentrations that we observed would, in my opinion, be useful in providing some degree of risk reduction against any disease for which the aerosol transmission is one of the infectious pathways. As a general principle, if the airborne concentration of a virus or bacteria is substantially reduced, the risk of contracting the disease through inhalation is also substantially reduced. In fact, for this very reason the conventional personal protective devices, such as personal masks and N95 respirators, are recommended by the US Centers for Disease Control and Prevention (CDC) and other agencies. The personal masks reduce the number of particles inhaled from the air contaminated with microorganisms (not aiming necessarily to achieve a zero-penetration). The airborne precautions were specified in the CDC document of May 1, 2003, entitled “Updated Interim Domestic Infection Control Guidelines in the Health-Care and Community Settings for Patients with Suspected SARS” (www.cdc.gov).
In the case of SARS, it is believed that aerosol transmission is one of the infectious pathways. During the CDC Telebriefing of May 15, Dr. Gerberding, the agency Director, stated: “there were opportunities for SARS virus to become airborne … it is imperative that we practice extreme vigilance in infection control precautions, that airborne contacts and standard procedures are appropriate in situations where patients with SARS are housed and that the droplet precautions that have been the primary focus need to be continue as well.” She also stated: “we can’t rule out the possibility of aerosol or airborne transmission, and so … we are emphasizing the extreme importance of vigilance to all levels of airborne protection” (CDC Telebriefing Transcript: Update on SARS, www.cdc.gov). The CDC recommended that the N95 respirator be used to protect against SARS transmission by the airborne route (Updated Interim Domestic Infection Control Guidelines in the Health-Care and Community Settings for Patients with Suspected SARS, www.cdc.gov).
The N95 respirator works by trapping at least 95% of airborne particles, thereby reducing the concentration of inhaled microorganisms. While based on a different principle and providing a time- and room-volume-dependent efficiency, the Wein ion generating equipment also reduces the concentration of aerosol particles in the breathing zone, thus providing a decrease in the exposure to indoor infectious aerosol agents.
Our ongoing manikin-based laboratory study addresses the situation when the respirator is being used in combination with an ionic air purifier operating in its vicinity. The aerosol concentration measurements are being conducted inside and outside the mask. The particle penetration
efficiency is determined as a function of time within the particle size range of 0.04 to about 3 microns. Among viruses and bacteria within this size range are coronavirus (SARS), which is between 0.06 to 0.22 µm, Variola major virus (Small pox), which is about 0.2 to 0.3 µm, and Bacillus anthracis bacteria (Anthrax), which is about 1 µm. The experiments have been set up in a room-size (25 m3) indoor test chamber utilizing “physical” particles. The natural aerosol concentration decay is taken into account in our study design. The preliminary data obtained with an inhalation rate of 30 liters of air per minute revealed that a unipolar ion emission near the respirator significantly enhances its performance, especially for small submicrometer particles.
The protection factor (the inverse of the particle penetration) of the N95 respirator with a perfect face fit was found to increase by about 50% due to the enhancement provided by the Automate™ AS1250B* unit. When a more powerful Vortex VI-3500* ion emitter was operating near the manikin’s face, the N95 protection factor increased more significantly allowing <1 % of aerosol particles to penetrate through the filter (instead of the 5% penetration threshold of the certified N95 respirator). Based on our preliminary data, I believe that the added electrostatic charges on the N95 fibers cause a significant enhancement effect (about 5-fold for the Vortex VI-3500* ionic purifier). I would expect this fiber-charge-driven enhancement effect to also manifest itself with other facemasks (e.g., with the common surgical mask that has lower collection efficiency than the N95 respirator). This statement needs to be experimentally verified. The laboratory tests involving surgical masks combined with ionic emitters are now in the planning stage with results expected in about two months.
I believe that when both effects (the indoor air concentration reduction and the respirator filter performance enhancement) are combined, the concentration of particles inhaled by a person wearing both a respirator mask and a Wein ionic air purifier would be reduced to a greater degree than if the person used the mask alone. This applies to all airborne particles in the tested size range.
Based on the currently available data, I would conclude that the aerosol concentration reduction, which results from operating the Wein ion emitters in indoor environments should further reduce the infection risk of airborne viruses or bacteria as compared to either completely unprotected breathing or to the inhalation protection provided by the N95 respirator alone. Depending on the infectious dose of a specific organism and its indoor aerosol concentration level, the risk reduction may be achieved for any agent within the size range of 0.04 to 3 microns, including coronavirus, Smallpox-causing virus and Anthrax-causing B. anthracis spores. I anticipate that the best results can be obtained when all the people in a room use ionic purifiers and wear personal protective mask. This should increase the overall efficiency for each individual exposed to an indoor air contaminant and minimize the cross-contamination effect
I recognize that although the major transmission route for SARS is still to be identified, it is presently thought to be spread by touch as well as by the aerosol transmission. Thus, reducing the concentration of airborne particulates should reduce the risk of infection. According to E.A. Nardell and J.M. Macher (Respiratory Infections – Transmission and Environmental Control – Chapter 9; IN: Bioaerosols: Assessment and Control, ACGIH, 1999), “the expected number of cases among a given number of susceptible persons is proportional to the average concentration of infectious droplet nuclei in a room and the probability that the particles will be inhaled” (p. 9- 6). Among the measures that can prevent or reduce airborne infection, the above experts list the control of the concentration of infectious agents in potential sources and maximizing removal rates of airborne infectious aerosols through dilution ventilation and use of air cleaners (p. 9-11). Numerous recently published documents, including the WHO (www.who.int) and CDC (www.cdc.gov) guidelines and recommendations, some of which were already quoted in this letter, as well as other materials (e.g., the SARS Clinical Information Sheet issued by the Johns Hopkins University on April 24, 2003), support this viewpoint.
I understand that the ions emitted from your purifiers charge aerosol particles and these particles move toward indoor surfaces and deposit on them. This suggests that the surface cleaning issue should be properly addressed when the equipment is used. As I have previously stated, the surface decontamination seems to be a less complex task than the air cleaning when the latter is done at very high efficiency levels. Although the particle resuspension from surfaces is generally acknowledged as a potential air contamination source, the efficiency of reaerosolizing viruses and bacteria is believed to be very low because of their small size. For infectious aerosols, “particles that contact a surface are assumed to adhere to it” (Nardell and Macher, p.9-10). The charged particles are especially difficult to resuspend. From my perspective as an aerosol scientist, it is of a primary importance to significantly reduce the aerosol concentration of infectious particles, which will subsequently decrease the probability that these particles would be inhaled and – as a result – will reduce the risk of adverse health effects.
Let me know if you have further questions. Sincerely,
Sergey A. Grinshpun, Ph.D.
Director, Center for Health-Related Aerosol Studies
*This document orginally pertained to the Vortex VI-2500, Minimate™ AS150MM, and Automate™ AS1250 Air Supply products, Wein Products, Inc.