Identification and containment of an outbreak of SARS in a community hospital

The World Health Organization reported1 as of April 28, 2003 that there are 5050 cases and 321 fatalities from Severe Acute Respiratory Syndrome (SARS). SARS has been suggested to be transmitted by aerosol droplet and possibly through other routes2. As a result of this form of transmission, it has been suggested that health care workers and others that may be potentially exposed2 employ respiratory and other personal protective equipment3,4. The type of respirator that has been used to protect health care workers from SARS is a N95 half-mask3,4. As correctly stated by Schabas the "N95-rated mask" is "95% filtration efficient...", which raises the question - does this provided the best protection for those potentially exposed? When working with chemical and biological warfare agents some have suggested that the N95 is inappropriate5 due to these respirators not "providing absorbent capability", and amount of mask leakage. This respirator can have leakage of about 5% through the filter and 10% around the mask6, even if properly fitted. For biological diseases, like SARS, that may only require only a few particles for infection, N95 may be inadequate and result in some health care workers becoming infected even though respirators were properly used.

A better selection for respiratory protection would be a N100 respirator with an ultra-low penetrating air filter (ULPA). The N100 respirator with an ULPA would have a slightly higher cost, but it would not be dramatic in comparison to cost associated with N95 respirators. N100 respirators have an efficiency (%) of 99.977. ULPA filters are 99.999% efficient for mono-dispersed particles that are 0.12 um in size or larger. HEPA filters would not be the best selection with a respirator because these filters are 99.97% efficient for mono-dispersed particles 0.3 um in size or larger and corona viruses have been shown to be less than 0.3um in size (around 60- 200 nm). For the N100 respirator to be effective with an ULPA the user must be fit tested. In the United States and many other countries there are numerous requirements for using a negative-pressure air-purifying respirator, including medical evaluation, training and fit testing once a year.

Thus, to afford the best protection for those potentially exposed to SARS, it is suggested that a higher efficiency respirator be employed. It is likely that the N95 will provide sufficient protection to most that use this type of respirator, but considering the size of the virus and its health implications, a higher efficiency respirator is warranted.

References

1. World Health Organization. Cumulative Number of Reported Probable Cases of Severe Acute Respiratory Syndrome (SARS) (April 28, 2003) www.who.int/csr/sars/en/

2. Dwosh HA, Hong HHL, Austgarden D, Herman S, Schabas. Identification and containment of an outbreak of SARS in a community hospital. www.cmaj.ca on April 25, 2003.

3. Schabas R SARS: prudence, not panic. Canadian Medical Association Journal 2003; 168: online1-2.

4.Centers for Disease Control. Update: severe acute respiratory syndrome - United States, 2003. MMWR 2003; 52: 357-60

5. GEOMET Technologies, Inc. Protection from Chemical and biological warfare. 2003, Germantown , MD, http://www.nbcprotection.com/new/geometarticles/protfrom chembiowarfare.htm.

6. Occupational Safety and Health Administration. Respiratory protective devices, part II, Final rule, US Federal Register 1995; 60: 30335-30398.

7. Colton CE, NelsonTJ. Respiratory protection. Chapter 36, pages 971 -1000, 1997, In The Occupational Environment - its evaluation and control. Edited by SR DiNardi, American Industrial Hygiene Association, Fairfax, VA