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TB Notes 1, 2000
Infection Control Issues
by Renee Ridzon, MD
Surveillance and Epidemiology Branch
In recent years, transmission of TB within the workplace has received
much attention in the scientific and popular press. However, the
notion of TB as an occupational hazard is not new, and since the
beginning of this century TB has been recognized as an occupational
hazard for doctors and nurses. In fact, there have been several
studies published in the first part of the 1900s documenting low
rates of M. tuberculosis infection among medical and nursing
students prior to the start of training. After completion of clerkships
caring for TB patients, high rates of tuberculin skin test conversions
and even cases of TB were seen. Concern about this occupational
risk waned, however, with the dramatic fall in the number of TB
cases in the US.
With the re-emergence of TB in the mid-1980s, the emergence of
multidrug-resistant TB (MDR TB), and recognition of the increased
morbidity caused by MDR TB and HIV-related TB, concern regarding
TB was reawakened in this country. Media reports about the danger
of TB were fueled by a number of published reports regarding explosive
outbreaks of MDR TB in hospitals, mostly in New York City, among
persons with HIV infection. Concern was further heightened by episodes
of transmission of disease to health care workers caring for the
patients involved in these outbreaks.
With recognition of the increased risk for TB among persons with
HIV infection, in 1990 CDC issued Guidelines for Preventing
the Transmission of Tuberculosis in Health-Care Settings with Special
Focus on HIV-Related Issues. Despite these guidelines, implementation
of appropriate infection control measures was incomplete in many
hospitals, and some of the published reports of nosocomial transmission
documented lapses in or absence of infection control measures in
the health care facilities. Because of its legal mandate to ensure
that no worker is harmed as a result of his or her work experience,
as well as the outbreaks of MDR TB, in 1992 the National Institute
for Occupational Safety and Health (NIOSH) recommended the use of
powered-air purifying respirators (PAPRs) by health care workers
potentially exposed to M. tuberculosis.
As a result of the ongoing outbreaks of TB and the NIOSH recommendation
for the use of PAPRs, the adequacy of the 1990 guidelines was discussed
at a large national meeting convened in 1993. In attendance at this
meeting were representatives from multiple groups concerned with
nosocomial transmission of M. tuberculosis, including infection
control practitioners, labor representatives, and occupational medicine
practitioners. The meeting concluded that in most of the outbreak
settings, the 1990 guidelines had not been adequately implemented,
and there was a need for revised and expanded guidelines. In 1993
a draft of the revised guidelines was published in the Federal
Register for public comment. After a period of comment and
public meetings, the report Guidelines for Preventing the Transmission
of Mycobacterium tuberculosis in Health-Care Facilities, 1994
was published in the Morbidity and Mortality Weekly Report.
This document contained detailed, comprehensive recommendations
for prevention of nosocomial transmission of M. tuberculosis.
Included in the recommendations was a hierarchy of controls composed
of, most importantly, administrative controls (including assignment
of responsibility, risk assessment, development of a TB infection
control plan with periodic reassessment, and tuberculin skin testing
of health care workers), followed by engineering controls, and then
by personal respiratory protection. Personal respiratory protection
devices that were recommended for use in the health care setting
needed to meet the following criteria:
At the time the 1994 guidelines were written, the only respiratory
protection device that was NIOSH-approved and met the above criteria
was the high efficiency particulate air (HEPA) filter respirators.
In July 1995 NIOSH updated its respirator testing and certification
requirements to permit the approval of other respirators. Under the
updated testing, respirators that contain a NIOSH-certified N-series
filter with 95% efficiency (N-95) rating meet the recommendations
of the CDC guidelines.
- ability to filter particles of 1 micron with a filter efficiency
- ability to be fit tested to obtain a face seal leak of 10% or
- ability to fit different face sizes, and
- ability to be checked for face-piece fit by health care workers
each time the respirator was used.
Image 1: Hierarchy of TB infection control measures
Like NIOSH, the Occupational Safety and Health Administration (OSHA)
has a legal mandate for the protection of workers; however, unlike
NIOSH, which can only issue recommendations, OSHA has the capacity
to enforce its standards. In 1997, OSHA published a draft TB standard
in the Federal Register. Following the publication of the
draft standard, there was a period for public comment followed by
a series of hearings for testimony. Detailed comments were submitted
from a CDC committee including staff members of NIOSH, the Hospital
Infections Program, and the Division of Tuberculosis Elimination,
as well as many other professional organizations. In July 1999,
OSHA reopened the docket for further public comment. The OSHA TB
standard is currently undergoing revision, and its final content
and release date are not yet known.
Image 2: Graphic of an example of personal respiratory protection
device for health care workers.
In order to better understand the risk of transmission of M.
tuberculosis to health care workers, CDC undertook several
studies designed to examine rates of skin test conversions in health
care workers. The most comprehensive of these was a study initiated
in 1995 called StaffTRAK-TB. This study included over 13,000 health
care workers. Data from this study demonstrate a rate of skin test
conversions among health care workers of 4.4 conversions per 1,000
person-years of follow-up. For US-born persons, the rate was even
lower at 3.2 conversions per 1,000 person-years. From data currently
available from studies such as StaffTRAK-TB, the risk of nosocomial
transmission of TB appears to be quite low. As a result CDC is considering
revision of the 1994 guidelines, especially in the areas of frequency
of tuberculin skin testing of health care workers.
The risk of transmission of M. tuberculosis in health
care settings is a real one. However, the magnitude of this risk
depends on many factors such as implementation of administrative
and engineering controls, prevalence of patients with infectious
TB within the facility, and risk for infection outside of the healthcare
facility. All of these factors need to be weighed in decisions regarding
recommendations or mandates for TB control measures within health
care facilities. As the rates of TB in the US continue to decline,
these recommendations will need to be tailored to offer protection
to patients and workers within the health care setting, without
an unnecessary burden of testing and expense.