Facing Airborne Infections
Health care workers' respirators must match the hazard to provide adequate protection.
- By Judith Green-McKenzie, M.D., MPH, FACOEM, FACP, David J. D'Souza, M.D., MPH, FACOEM
- May 01, 2006
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.
Some of the disadvantages of using respirators are that, depending on the type used, they may interfere with vision, hearing, the ability to communicate, or with the use of tools such as stethoscopes. They may also lead to anxiety and interfere with mobility; moisture and warmth may build up inside the mask if there is a tight fit over the face. The respirators' elastic head straps may also cause discomfort. Negative pressure respirators increase resistance to inspiration and the work of breathing, to some extent. In general, respirators place a strain on the worker, hence the need for a medical evaluation.1,2
Some of the airborne biological hazards against which respirators will provide protection are TB, smallpox virus, and avian influenza. TB is a common infection and, in fact, remains the most frequent cause of death due to an infectious agent in people worldwide.3 Its documented presence as a human disease dates to more than 3,000 years ago, having been found to cause disease in mummies in ancient Africa.4 The Greeks were also familiar with this chronic disease, referring to it as "consumption."
Environments other than health care that are traditionally considered as high-risk occupational groups for TB include correctional facilities, homeless shelters, long-term care facilities for the elderly, and drug treatment shelters.5 However, occupational exposure to TB may occur in other occupational settings, including farms, zoos, circuses, and research settings. Animals such as cows, goats, elephants, rhinoceroses, and monkeys are susceptible to TB and can transmit TB to humans. TB is transmitted by infectious droplets suspended in mid-air that have been expelled when a person with active disease in the lung sneezes, talks, or coughs. The susceptible person becomes infected about four to 12 weeks after exposure, although the infection may remain dormant with a 10 percent chance of its becoming active over the course of the person's lifetime.
Respirators labeled N95 meet the minimum filtration performance for respiratory protection against TB and are to be used in areas where patients with suspected or confirmed tuberculosis may be present. This negative-pressure, non-powered, air-purifying, half-facepiece respirator, with a filter efficiency of at least 95 percent, must be of a type certified and approved by the National Institute for Occupational Safety and Health. Health care settings are generally free from oil aerosols that would degrade filter efficiency, so N, P, or R respirators are appropriate to be used in order to protect against TB. The types of N95 respirators available vary according to cost, comfort, and fit-test data. Surgical masks are not respirators and are not certified as such. They do not adequately protect against TB.1,2
Respiratory protection must be worn by hospital employees entering rooms where patients with known or suspected infectious TB are being isolated; by employees present during cough-inducing or aerosol-generating procedures performed on patients; during the performance of high-hazard procedures; when emergency personnel transport an individual with confirmed or suspected TB in a closed vehicle; and by persons in other settings where administrative and engineering controls are not likely to protect them from inhaling infectious airborne droplet nuclei.
In situations where the risk of exposure to TB is increased, such as during bronchoscopy or other procedures inducing cough and leading to aerosol generation, more protective respirators, such as an N100 or a powered air-purifying respirator with a high-efficiency particulate air (HEPA) filter, may be needed. Latex-free respirators are now available for latex-allergic individuals.1,2
OSHA has regulated respiratory protection against TB since 2004 under the general industry standard. Although this standard requires annual fit testing, Congress through fiscal year 2005 appropriations prohibited OSHA from using funds to administer or enforce this annual fit-testing requirement for TB respirators.6 Some infectious disease experts involved in infection control in hospital settings feel there is insufficient evidence to support annual/periodic fit testing for protection from biological agents, such as TB. Also, for small facilities or where TB is rarely encountered, this annual requirement may pose a burden requiring resource allocation to this end. As of this writing, Congress has not extended the ban on enforcement, which means health care settings would need to be in compliance with the standard and its annual fit testing requirement. The Centers for Disease Control and Prevention issued draft guidelines in 2005 for preventing the transmission of Mycobacterium tuberculosis in health care settings, recommending periodic fit testing for N95 respirators but not stating how often it should be done.
Employees wearing respirators in occupational settings for protection against TB need to be a part of a respirator protection program. Hospitals may perform pre-placement fit testing for N95 respirators and perform annual fit testing, using their own staff or external consultants, in order to comply with the OSHA standard. The educational component of the respirator program may be performed by in-house staff or consultants or by video training.
Other Airborne Infections
Smallpox (variola major) is another disease transmitted by the airborne route. This highly contagious disease is characterized by fever, a vesicular and pustular eruption, and a high mortality rate. There have been no reported cases since the global eradication of smallpox was announced in 1979, but the potential use of smallpox as an agent of bioterrorism is of concern.
The oropharynx of the infected person serves as the reservoir for virus spread. CDC recommends that health care workers caring for infected patients wear a fit-tested N95 respirator, disposable gown, shoe covers, and gloves before entering the contaminated area. The protective clothing must be disposed of before leaving the area. Individuals selected to work with patients who have smallpox must have no contraindications to the smallpox vaccine.
Highly pathogenic avian influenza viruses, which have produced outbreaks among poultry and also caused human infection in some people exposed to poultry, are an emerging concern, especially because sporadic transmission from poultry to humans has occurred. The World Health Organization has described the threat from avian influenza virus as a public health crisis. Clinical features of avian influenza include pneumonia and other lower respiratory symptoms and diarrhea. It is associated with a high mortality rate, high incidence of pneumonia, and a high rate of intensive care.
SARS, a rapidly progressive illness first seen in Guangdong Province in China, is an airborne biological hazard that has recently emerged. It is spread primarily by close person-to-person contact with symptomatic individuals (e.g., persons with fever or respiratory symptoms) or by airborne droplet transmission. Symptoms include fever with or without rigors, cough, malaise, headache, myalgias, shortness of breath, and pneumonia. CDC recommends that Airborne Precautions and Standard Precautions be instituted for infected hospitalized patients, and that health care workers and visitors wear N95 respirators to prevent airborne and droplet acquisition, as well as gowns, gloves, and protective eyewear to guard against transmission.
N95 respirators, although disposable, can be reused by the same health care worker.7 However, it may be difficult to reuse a disposable respirator without contaminating it. Hand hygiene should be performed after removing a respirator or after replacing a respirator on the face. Respirators should be changed if they are deformed and no longer provide an adequate fit or if they are soiled or splashed with blood products, for example. While there is no evidence to suggest that infectious particles in the filter material are easily re-aerosolized, CDC has advised that disposable respirators be discarded once used in the presence of a SARS patient. Therefore, it is important to follow CDC and local infection control guidelines regarding reuse of respirators, as well as follow manufacturers' recommendations.
In summary, some of the airborne biological hazards for which a respirator provides protection are TB, smallpox virus, avian influenza, and SARS. The minimum respiratory personal protection for these respiratory pathogens is a NIOSH-approved N95 particulate respirator. PAPRs, which use HEPA filters (as efficient as P100 filters), provide a higher level of protection than the disposable N95 respirators and may be used if warranted. In the event of a bioterrorism attack or public health emergency, a hospital should have a rapid fit-testing plan. CDC and local infection control guidelines, as well as manufacturers' recommendations, should be followed, and input from an industrial hygienist should be sought.
This article appeared in the May 2006 issue of Occupational Health & Safety.
1. Code of Federal Regulations, Respiratory Protection. Title 29, CFR, Part 1910.134. Washington, DC: US Government Printing Office, Office of the Federal Register. 2003, 420-45.
2. Harber P, Barhart S, et. al. 2005. "ATS guidelines: Respiratory protection guidelines." In: UpToDate. Available: http://www.uptodate.com [accessed Nov. 11, 2005].
3. Dye C, Scheele S, Dolin P, et al. "Consensus statement: Global burden of Tuberculosis: Estimated incidence, prevalence and mortality by country: WHO Global Surveillance and Monitoring Project." JAMA. 1999, 282:677-686.
4. Nerlich AG, Hans CJ, Zink A, et al. "Molecular evidence for tuberculosis in an ancient Egyptian." Lancet. 1997, 350:1404.
5. Centers for Disease Control. "Guidelines for preventing the transmission of Mycobacterium tuberculosis in health-care facilities." MMWR. 1994, 43 (No. RR-13).
6. US Department of Labor OSHA Standard Interpretations--Tuberculosis and Respiratory Protection: prohibition of enforcing annual fit testing requirements during 2005 fiscal year; enforcement of other 1910.134 provisions. Available at: www.osha.gov [accessed Nov. 11, 2005].
7. Centers for Disease Control. (Draft) "Guidelines for preventing the transmission of Mycobacterium tuberculosis in health-care settings, 2005." Available at: www.cdc.gov, [accessed Nov. 22, 2005].
The authors would like to thank J. Passante, CIH, for his helpful comments.
This article originally appeared in the May 2006 issue of Occupational Health & Safety.