Facing Airborne Infections
- By Judith Green-McKenzie, M.D., MPH, FACOEM, FACP, David J. D'Souza, M.D., MPH, FACOEM
- May 01, 2006
Health care workers' respirators must match the hazard to provide adequate protection.
RESPIRATORS are essential personal protective equipment for protection against some airborne biological hazards in health care settings, tuberculosis (TB), the virus causing severe acute respiratory syndrome (SARS), avian influenza, and smallpox virus among them. Airborne droplet nuclei (small-particle residue 5 microns or less in size) generated from the respiratory tract while an infectious patient coughs or sneezes is a potential source of hospital infections because microorganisms carried in this way may remain suspended in the air for long periods of time and can disseminate over a wide area carried by air currents. These infectious agents are either directly inhaled or indirectly acquired through contaminated medical devices.
In addition to respirator use, Airborne Precautions, designed to reduce the risk of airborne transmission of infectious agents, and Standard Precautions, designed to reduce the risk of transmission of microorganisms from both recognized and unrecognized sources of infection in hospitals, are also implemented. One of the main requirements of Airborne Precautions is placement of the infectious patient in a negative-pressure private room. Standard Precautions include strict hand washing; proper disposal of needles and other sharps; and the use of appropriate PPE, such as gloves, masks, and resuscitation barriers, when indicated.
Respirator Types, Testing
The concept of respirators has been around for centuries, dating back at least to Roman times, when pig bladders were used to protect against lead. Today, there are two main types of respirators: the air-purifying respirator and the atmosphere-supplying respirator. The air-purifying respirator removes contaminants from inhaled air by filtration, adsorption, or absorption. Air may be pulled through a filter by a powered source, as in the powered air-purifying respirator (PAPR), or by negative pressure, where the user pulls air through the respirator. The atmosphere-supplying respirator provides clean, breathable air from an uncontaminated independent source as opposed to purifying ambient air.
There are two types of atmosphere-supplying respirators: the self-contained breathing apparatus (SCBA), which supplies air from a source such as a tank carried by the user, and the airline respirator, which uses air supplied by a hose from a distant source.1
The filters used on a respirator have three levels of filter efficiency (the stated percentage of particles removed from air): 95 percent, 99 percent, and 99.97 percent. A filter labeled as having 95 percent filter efficiency means that it is at least 95 percent efficient in removing particles 0.3 microns or greater in size from the air. Similarly, there are three categories of resistance to filter efficiency degradation (reduction in the ability of the filter to remove particles as a result of workplace exposure), referred to as N, P, and R. N means not resistant to oil, R means resistant to oil, and P means oil proof. There are nine resultant classes of filters using these three levels of filter efficiency and three levels of filter efficiency degradation. The filter, the filter package, or the respirator box will be labeled with the class of the filter. Masks are quarter-, half-, or full-face, depending on the portion of the face that is covered.1,2
The degree of protection that a respirator gives depends on how efficiently contaminants are removed from the outside air by the respirator, how well the respirator fits the individual, and how well leaks through the face seal, valves, and other elements are prevented. Most respirators require a tight seal between the mask and the user's face. Loose-fitting respirators do not require such a seal. OSHA's general industry respiratory standard (29 CFR 1910.134) requires that workers undergo respirator fit testing prior to using the respirator selected to match the hazard. Loose-fitting respirators and disposable dust masks worn voluntarily by employees do not require fit testing.
Some of the other elements of the respirator standard are that the employer establish a respirator program, that the employer select a physician or licensed health care provider to perform a medical evaluation on the employee in order to assess whether the employee should be medically cleared to wear a respirator, and that the employee be trained in the use of the respirator. During the medical clearance portion of this process, a lengthy questionnaire is used asking about issues such as claustrophobia, problems with vision or hearing, heart or lung disease, or skin allergy. Annual employee training and fit testing is required when OSHA or the employer requires employees to wear tight-fitting respirators. The expertise of an industrial hygienist should be employed when deciding on the proper respirator to fit the hazard.1,2 Infection control and IH personnel should decide which categories of employees are to be fit tested.
This article originally appeared in the May 2006 issue of Occupational Health & Safety.