- © 2004 Canadian Medical Association or its licensors
In previous letters1,2 I suggested that proper use of an N100 respirator provides the best protection against SARS. The US Centers for Disease Control and Prevention (CDC) recently reported that the SARS virus can be transmitted by fomites and aerosols and that infection can occur via the mucous membranes of the mouth and eyes (the conjunctiva).3 The CDC report3 recommended use of an N95 respirator (a half-mask) for protection against SARS, but the finding that transmission can occur through the eyes indicates that a half-mask respirator is not appropriate for this purpose. This conclusion is supported by 3 other recent publications4,5,6 reporting that N95 respirators do not appear to be effective. This ineffectiveness is due to the particle size of the SARS virus, poor fit and inadequate eye protection. Instead, use of an elastomeric (rubber) full-face respirator with an ultra-low penetrating air (ULPA) filter, rather than a high-efficiency particulate air filter, is warranted (e.g., North full-face respiratory 7600 series, see www.websoft-solutions.net/ProductDetails.asp?ProductCode=Nr7600Ser). Ideally, the full-face respirator will have a double seal for better fit to the face and to reduce leakage. The full-face respirator has the advantage of protecting the mucous membranes of the face, whereas N95 and N100 respirators do not offer this protection. Protection of the entire face, including the eyes, is especially important, given that it has been suggested that infection occurs through this route.7 The disadvantages of this type of respirator are the cleaning, disinfection and maintenance requirements.
Use of a full-face respirator affords the highest level of protection without employing a positive-pressure respirator system. A full-face respirator combined with a ULPA filter provides the most practical and cost-effective protection against airborne particles such as the SARS virus. Although the full-face respirator costs more than a disposable N95 respirator (about US$120 v. US$5), the greater risk of infection with the N95 respirator justifies the extra cost.
John H. Lange Envirosafe Training and Consultants, Inc. Pittsburgh, Pa.
Footnotes
-
Competing interests: None declared.