[Table of Contents]

Volume: 22S1 • April 1996

Guidelines for Preventing the Transmission of Tuberculosis in Canadian Health Care Facilities and Other Institutional Settings

IV. TB MANAGEMENT PROGRAM

F. Personal Respiratory Protection (Masks)

Personal respiratory protective devices (PRPDs) include surgical masks and particulate respirators (e.g., HEPA filter, dust-mist and dust-mist-fume masks). In this document, they are referred to as masks. Masks may provide additional protection against TB transmission when HCWs care for patients with suspected or confirmed infectious TB. Currently, the controversy concerning the effectiveness of various types of masks in protecting against TB transmission is illustrated by the number of different, and sometimes conflicting, recommendations that have been published from 1990 to 1995^{(36,45,79-84)}. National guidelines issued in 1994 from the U.S. (that only recommended HEPA filter masks approved by the National Institute for Occupational Safety and Health (NIOSH))⁽³⁶⁾ and U.K. (recommending no masks)⁽⁸³⁾ illustrate very different positions on this issue.

The precise requirements for effective TB respiratory protection cannot be determined with currently available data for a number of reasons. Patients with TB vary in their level of infectivity. Exposed individuals vary in their degree of susceptibility (see Section III). The smallest infectious dose that results in transmission of TB has not been determined but, in theory, one organism can cause infection^(36,75,85). The highest level of exposure to M. tuberculosis at which transmission will not occur has also not been defined⁽³⁶⁾. These factors are further complicated in that the duration and type of exposure that HCWs have to patients with TB also vary (see Section IV.D.7).

According to theoretic considerations based on particle size, an appropriate mask for respiratory protection against TB should be able to meet or exceed the following recommendations:

• filters particles one micron in size (infectious TB particles are one to five microns in size);

• has a 95% filter efficiency, tested in the unloaded state; and

• provides a tight facial seal (less than 10% facial seal leak).

The effectiveness of any mask is a function of all of the above factors. For the mask to filter out the droplet nuclei, the air must pass through and not around the mask. When gaps are present between the face and the mask resulting in a poor facial seal, air will preferentially flow through the gaps and bypass the mask filter. Higher efficiency masks that do not fit tightly have high rates of air leakage that lower the overall efficiency of the device^(79,80). For example, a mask with a 90% filtering efficiency that has a 10% face-seal leak will be as effective as a mask with a 99.97% filter efficiency that has a 20% face-seal leak⁽³⁶⁾.

Types of Masks

Surgical masks are effective in decreasing aerosolization of exhaled infectious particles. Patients with suspected or confirmed infectious TB should use surgical masks (or a more efficient mask that does not have a expiratory valve) during transport or when they are required to leave the isolation room. Surgical masks effectively filter less than 50% of inhaled particles that are one to five microns in size and have marked leakage because of loose facial seals. Thus, surgical masks may not prevent the inhalation of droplet nuclei^(86,87). In the United States, NIOSH refers to surgical masks as "masks".

N.B. NIOSH now uses the term "respirator" to refer to equipment worn by health care workers for respiratory protection. In this document, the term "mask" is used to refer to respiratory protective equipment worn by patients or health care workers.

In July 1995, NIOSH instituted a new respirator (mask) certification program (42 CFR part 84) to certify respirators⁽⁸⁴⁾. The NIOSH program no longer uses the terms dust-mist masks and dust-mist-fume masks. Instead, it identifies three classes of respirators called Class N, R, and P. Each certified respirator has been tested to determine filtration at a 95%, 99% or 99.97% (referred to as 100%) degree of efficiency of a penetrating aerosol particle (0.3 microns in size) in the unloaded state. An updated list of NIOSH certified respirators can be obtained by writing to Richard Metzler, Chief, Certification and Quality Assurance Branch, Division of Safety Research NIOSH, 1095 Willowdale Road, Morgantown, West Virginia, 26505-2888 or by obtaining the list on the INTERNET (address: http://www.cdc.gov/niosh/homepage.htm1). Provided that an adequate facial seal is present, respirators that are NIOSH certified as N95, N99, N100, R95, R99, R100, P95, P99, and P100 meet or exceed the minimum recommendation for health care worker masks listed above in section F.

Personal powered respirators are generally not recommended for the care of patients with TB.

Facial Fit

HCWs should be fitted and educated regarding the proper way to wear a mask to ensure a tight facial seal. It has been recommended that formal fit testing be carried out, upon employment, at least annually, or whenever conditions necessitate a change in the type of mask available^(36,88). There are a variety of fit-testing methods. The adequacy of a facial seal may be determined, for example, by formal fit-testing methods (e.g., saccharine testing⁽⁸⁹⁾) or by informal testing methods (fit check) where the wearer tests the fit by taking a quick forceful inspiration to determine if the mask seals tightly to the face.

Because of variability in facial structure in the Canadian population, more than one size, make, or model of mask may need to be provided to ensure that a properly fitting mask is available for all users. Even for the same individual, fluctuations in weight may affect the facial seal of a mask and alter which mask fits best. Poor facial seal has been documented in individuals with full beards.

Wearer Acceptance

In evaluating the effectiveness of a mask, wearer acceptance should be considered. HCWs should be consulted about the following factors:

• comfort;

• interference with communication;

• resistance to breathing;

• fatigue;

• interference with vision;

• interference with job performance; and

• confidence in the device's effectiveness.

Recommended Use of Masks

Masks should be used by individuals (HCWs and others) when:

• caring for a patient with suspected or confirmed infectious TB;

• entering a room where a patient with suspected or confirmed infectious TB is being isolated;

• a patient with suspected or confirmed infectious TB is undergoing a procedure that is likely to produce aerosolized infectious particles or to result in coughing or copious sputum production, even if appropriate ventilation is in place;

• in contact with a patient with signs and symptoms that suggest infectious TB (e.g., during ambulance transport or transport in protective custody);

• manipulating mycobacterial cultures in the laboratory; and

• performing an autopsy (see Section VI).

[Previous] [Table of Contents] [Next]