Letter to the editor:
Letter to the editor:
[Editor's note: In June, HEH reported on interim guidance on respiratory protection issued by the Centers for Disease Control and Prevention (CDC) in Atlanta for a bioterrorism exercise. The CDC said surgical masks would provide adequate protection against plague during such an attack, but advised that the additional protection provided by N95 filtering facepiece respirators would be "prudent." The guidance also noted that "exigent circumstances" during a large-scale event might require suspension of fit-testing and medical clearance requirements. This letter to the editor is a response to that article.]
The CDC's interim guidance regarding personnel protection equipment (PPE) for respiratory infections is confusing because the wrong experts are making selection decisions based on the wrong criteria. Their algorithms are based on disease-specific organisms, which typically are not ascertained until long after significant exposures have occurred. When febrile/coughing patients present, they do not do so conveniently diagnosed, with labeled organisms in hand.
Furthermore, health care workers need personal protection that is proved effective based on particle/aerosol physics-based experimentation, not a "guidance… based on historical and modern information on transmission patterns of naturally occurring illnesses." There was no historical pattern for SARS.
Infectious organisms, irrespective of their pathogenicity, are particles that obey the laws of physics. Pathogens in the air behave no differently than other particles of similar physical properties. Their infectious natures are of no consequence if they do not enter the body.
Some of the variables that determine the risk of contamination are: size, shape, concentration, relative humidity, ventilation/airflow/air exchanges/turbulence, electrostatic forces, and filtration efficiency/effectiveness. There are numerous scientific experiments that demonstrate the superior protection offered by N95 respirators1-11.
Not only are the CDC guidelines disease-specific, but they make an unequivocal distinction between droplet and airborne diseases, whereas in reality, as a consequence of the aforementioned variables, the actual aerodynamics are rather on a continuum: A droplet can become airborne with turbulent airflow and/or low relative humidity. The right parameters will keep even hail buoyant.
In private communications with local authorities and with the CDC, and in my public submissions to the SARS Commission12 regarding respiratory containment, isolation, and PPE, I have suggested that much more input be sought from, and credence be given to, biosafety experts, aerosol physicists, ventilation engineers, and occupational hygienists.
Consequent conclusions and recommendations would be based on sound and proven principles and experimentations; the resultant guidelines would be less confusing and controversial and be more credible. Input from respiratory safety officers and occupational health specialists would help to address the human resource demands and the logistical exigencies of an effective respiratory protection program.
Gabor Lantos, MD, PEng, MBA
President, Occupational Health Management Services
Toronto
References
1. Grinshpun SA, Mainelis G, et al. Sampling of biological aerosols: particle collection efficiency and survival of viable microorganisms. Proceedings of the 1st Asia Aerosol Conference, Nagoya, Japan, July 27-29, 1999.
2. Qian Y, Willike K, et al. Performance of N95 respirators: Filtration efficiency for airborne microbial and inert particles. Am Ind Hyg Assoc J 1998; 59:128-132.
3. Hinds, WC. Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles. 2nd Ed., 1998, New York: Wiley-Interscience.
4. Lee BU, Yermakov M, and Grinshpun SA. Filtering efficiency of N95- and R95-type facepiece respirators, dust-mist facepiece respirators, and surgical masks operating in unipolarly ionized indoor air environments. International Journal for Aerosol and Air Quality Research 2005; 5:27-40.
5. Qian Y, Donelly J, et al. Performance of N95 respirators: Reaerosolization of bacteria and solid particles. Am Ind Hyg Assoc J 1997; 58:876-880.
6. Reponen TA, Wang Z, et al. Survival of Mycobacteria on N95 respirators. Infect Control Hosp Epidemiol 1999 20(4):237-241.
7. Sergey A, McKay R, et al. How to increase the protection factor provided by existing facepiece respirators against airborne viruses: a novel approach. Proceedings of the European Aerosol Conference (Budapest, Hungary Sept. 5-10, 2004), Journal of Aerosol Science, EAC, 2:1263-1264.
8. Sergey A, Reponen TA, Grinshpun SA, Respiratory protection against airborne biological agents. Perspectives on Biodefense, University of Cincinnati, Oct. 29-30, 2004.
9. Wang Z, Gorny RL, et al. Effect of sampling time and air humidity on the bioefficiency of filter samplers for bio-aerosols. J Aerosol Science 2001; 32:661-674.
10. Weber A, Willeke K, et al. Aerosol penetration and leakage characteristics of masks used in the healthcare industry. Am J Infect Control 1993; 21:167-173.
11. Willeke K, Quian Y, et al. Penetration of airborne microorganisms through a surgical mask and a dust/mist respirator. Am Ind Hyg Assoc J 1996; 57:348-355.
12. Lantos, G., submissions transcripts: www.sarscommission.ca, Nov. 17, 2003.
The CDC's interim guidance regarding personnel protection equipment (PPE) for respiratory infections is confusing because the wrong experts are making selection decisions based on the wrong criteria.Subscribe Now for Access
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