NIOSH Recommended Guidelines for Personal Respiratory Protection of Workers in Health-Care Facilities Potentially Exposed to Tuberculosis/I. Introduction
I. Introduction
In January 1992, the CDC Tuberculosis Working Group asked that NIOSH "take the lead" in developing guidelines for appropriate personal respiratory protection, i.e. respirators, to protect workers in health-care facilities from occupational transmission of tuberculosis. In addition to consideration of the complex technical issues of respiratory protection which follow, NIOSH personnel also gave careful thought to our understanding of the current epidemiology and control of tuberculosis, to the directives to NIOSH embodied in the Occupational Safety and Health Act of 1970, and to the operational philosophy of prudent public health practice.
A. Current Epidemiology and Control of Tuberculosis―Summary information on the transmission of tuberculosis was reported by CDC in 1991 (1):
The number of tuberculosis cases reported to CDC has been increasing since 1988, after a long historic decline. In 1990, 25,701 cases were reported, an increase of 9.4% over the 1989 figure and the largest annual increase since 1952. From 1985 to 1990, reported cases increased by 15.8%. Disproportionately greater increases in reported cases occurred among Hispanics, non-Hispanic blacks, and Asians/Pacific Islanders. In contrast, decreases were observed among non-Hispanic whites and American Indians/Alaskan Natives. By age, the largest increase in reported cases occurred in the 25- to 44-year age group; this increase may be largely attributable to rising numbers of tuberculosis cases among persons with human immunodeficiency virus infection or acquired immunodeficiency syndrome. Notable increases also occurred among children.
Snider and Roper later provided the following caution (2):
Events during the past decade have changed the nature and magnitude of the problem of tuberculosis. Much of what many physicians learned in training about this disease is no longer true. In many respects, tuberculosis has become a new entity.
In 1992, CDC reported that (3):
A person who becomes infected with TB bacillus remains infected for years. Usually a person with a healthy immune system does not become ill, but is usually not able to eliminate the infection without taking an antituberculosis drug. This condition is referred to as "latent tuberculosis infection." Persons with latent tuberculosis infection are asymptomatic and cannot spread TB to others. Generally, a positive TB skin test is the only evidence of infection. About 10-15 million persons in this country are infected with M. tuberculosis.
According to the American Medical Association, about 70% of infectious tuberculosis cases occur among racial and ethnic minorities, and (4):
About 10% of infected persons will develop active tuberculosis at some time in their lives; approximately 5% will develop active disease within the first two years. In the absence of treatment, case fatality is about 50% in five years ... Patients with drug susceptible strains of tuberculosis can be successfully treated with a three-drug regimen of INH [isoniazid], RIF [rifampin], and PZA [pyrazinamide] given for six months with a 95% cure rate, as previously discussed.
Difficulties have arisen in ensuring a continuing supply of antituberculosis drugs in the United States due to uncertain supplies of isoniazid and other drugs (2,5).
Recently, multiple-drug-resistant tuberculosis (MDR-TB) has become a serious concern (4,6). Multiple-drug-resistant is defined as resistance to two or more primary drugs used in this country for the treatment of tuberculosis (currently isoniazid, rifampin, pyrazinamide, streptomycin, and ethambutol). In a recent survey in New York City, 33% of tuberculosis cases had organisms resistant to at least one drug, and 19% had organisms resistant to both isoniazid (INH+) and rifampin, the two most effective drugs available for treating tuberculosis. When organisms are resistant to both INH and rifampin, the course of treatment increases from 6 months to 18-24 months, and the cure rate decreases from about 95% to 60% or less.
Against this background of increasing numbers of tuberculosis cases and increasing numbers of multiple-drug-resistant cases, CDC has reported a serious new phenomenon: outbreaks of MDR-TB in institutional settings. From 1990 through early 1992, in collaboration with state and local health departments, CDC investigated numerous outbreaks of MDR-TB in hospitals and correctional facilities in Florida and New York (7,8,9). To date, these outbreaks have included over 200 tuberculosis cases. Virtually all of these cases have had organisms resistant to both INH and rifampin, and some have had organisms resistant to up to seven antituberculosis drugs. Most of the patients in these outbreaks were infected with HIV. Mortality among patients with MDR-TB in these outbreaks has been very high, ranging from 72 to 89%, and the median interval between diagnosis and death has been very short, from 4 to 16 weeks.
In addition to hospitalized patients and inmates, occupational transmission of MDR-TB to health-care-facility workers and prison guards has been documented. At least nine of these workers have developed clinically active MDR-TB, and five of them have died. Of the eight health-care-facility workers who developed clinically active MDR-TB, five were known to be infected with HIV (8).
The continuing occupational hazard of tuberculosis infection in health-care-facilities in conjunction with the continuing outbreaks of tuberculosis in health-care-facility workers led NIOSH to reexamine the role of personal respiratory protection in preventing occupational transmission of tuberculosis infection in health-care settings. There is a paucity of data from well-designed studies regarding both the efficacy and reliability[1] of precautions such as administrative controls, ventilation systems, and particulate respirators (PRs) that are currently recommended (10). Regarding the efficacy of ventilation and respirators currently recommended, the following report was given in a summary of a January 1992 conference (11):
Data are urgently needed to assess the efficacy of the various isolation procedures currently recommended in facilities. The effectiveness and relative importance of ventilation, ultraviolet lights, particulate respirators, and
isolation booths must be determined. In the absence of definitive data, "best judgment" recommendations should be developed, perhaps with assessment of the category of proof (strength of evidence) of efficacy, as in the current CDC guidelines for infection control and isolation (12).
CDC recently concluded that (3):
The efficacy of various technologies for preventing TB transmission (e.g., general and local ventilation, UVGI, and personal protective equipment) has not been adequately evaluated.
B. The Mandates to NIOSH in the Occupational Safety and Health Act of 1970—The Occupational Safety and Health Act of 1970 established the right to safe and healthful working conditions for every working man and woman, and the obligations to provide work and a workplace which are "free of recognized hazards." In its opening paragraphs Congress declared its purpose in passing the Act to be (13):
...to assure so far as possible every working man and woman in the Nation safe and healthful working conditions and to preserve our human resources—...
In Section 20 of the Act, Research and Related Activities, which defines the responsibilities of NIOSH, the Act requires that the Director of NIOSH (13):
...on the basis of such research, demonstrations, and experiments, and any other information available to him, shall develop criteria dealing with toxic substances which will describe exposure levels that are safe for various periods of employment ... exposure levels at which no employee will suffer impaired health or functional capacities or diminished life expectancy as a result of his work experience. (emphasis added)
This mandate sharply defines the obligation of NIOSH to formulate science-based assessments of risk and preventive recommendations which, if implemented, would assure that no worker develops illness as a consequence of exposure at work. Specifically, as regards the occupational transmission of tuberculosis in health-care facilities, NIOSH interpreted its mandate as recommending, where necessary, the use of personal respiratory protection that would assure that no worker will be infected with tubercle bacillus as a result of occupational exposure. As applied to tuberculosis, this mandate is especially demanding because there is no consensus among experts as to the number, if any, of droplet nuclei containing tubercle bacilli which can be safely breathed by a susceptible worker. Hence, to assure that "no worker will suffer" occupational infection with tubercle bacillus requires the formulation of recommendations which, if implemented, would reduce to the minimum the probability of air contaminated with droplet nuclei being shared between a person with infectious tuberculosis and a worker. The recommendations in this document represent the approach to prevention which most nearly enables NIOSH to meet the directives explicit in the Occupational Safety and Health Act of 1970.
C. The Principle of Public Health Prudence—Traditionally, in addition to careful adherence to its mandates in the Occupational Safety and Health Act of 1970, NIOSH has developed its recommendations for prevention in accord with an operational philosophy which may be called "the principle of public health prudence." Loosely stated, this principle holds that "when faced with uncertainty, it is better to err in favor of human life and health than in favor of any competing value." In the context of NIOSH recommendations for the protection of workers, the principle may be restated as an informal NIOSH operating policy that "faced with scientific uncertainty, if we must err, it will always be on the side of too much protection for the worker rather than too little." This philosophy is supported in a court decision that OSHA and the Nation's courts "cannot let workers suffer while it awaits the Godot of scientific certainty" (14).
NIOSH fully accepts that the evidence available is not adequate to confidently assess both the efficacy and reliability of various currently recommended procedures for preventing the transmission of tuberculosis in health-care facilities. Given the absence of definitive data, particularly for the particulate respirators (PRs) now recommended for use in health- care facilities, NIOSH has, on the basis of the well-documented mode of airborne transmission of tuberculosis, scientific and technical logic, and broad experience with personal respiratory protection programs in a variety of occupational settings, attempted a "best judgement." This is consistent both with NIOSH's mandates and prudent practice in the workplace.
- ↑ Reliability is the probability that an individual wearer will receive adequate protection against airborne tuberculosis transmission over the reasonably-anticipated "life span" of the "protection system" (e.g., days, weeks, months, years of wearing respirators) during which the personal protection must be relied upon under conditions of use that can be reasonably anticipated (e.g., training, fitting, use, and maintenance).