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eral ventilation that results in insufficient dilution transmission of M. tuberculosis in those facilities in
and/or removal of infectious droplet nuclei; and c) which immunocompromised persons (e.g., HIV-in-
recirculation of air containing infectious droplet nu- fected persons) work or receive care—especially if
clei. Characteristics of the persons exposed to M. tu- cough-inducing procedures, such as sputum induc-
berculosis that may affect the risk for becoming in- tion and aerosolized pentamidine treatments, are
fected are not as well defined. In general, persons being performed.
who have been infected previously with M. tubercu-
losis may be less susceptible to subsequent infection. Several TB outbreaks among persons in health care
However, reinfection can occur among previously facilities have been reported recently (11,24-28;
infected persons, especially if they are severely CDC unpublished data). Many of these outbreaks
immunocompromised. Vaccination with Bacille of involved transmission of multidrug-resistant strains
Calmette and Guérin (BCG) probably does not af- of M. tuberculosis to both patients and HCWs. Most
fect the risk for infection; rather, it decreases the risk of the patients and some of the HCWs were HIV-in-
for progressing from latent TB infection to active TB fected persons in whom new infection progressed
(13). Finally, although it is well established that rapidly to active disease. Mortality associated with
HIV infection increases the likelihood of progress- those outbreaks was high (range: 43%-93%). Fur-
ing from latent TB infection to active TB, it is un- thermore, the interval between diagnosis and death
known whether HIV infection increases the risk for was brief (range of median intervals: 4-16 weeks).
becoming infected if exposed to M. tuberculosis. Factors contributing to these outbreaks included de-
layed diagnosis of TB, delayed recognition of drug
C. Risk for Nosocomial Transmission of M. tuber- resistance, and delayed initiation of effective
culosis therapy—all of which resulted in prolonged infec-
tiousness, delayed initiation and inadequate dura-
Transmission of M. tuberculosis is a recognized risk tion of TB isolation, inadequate ventilation in TB
in health care facilities (14-22). The magnitude of isolation rooms, lapses in TB isolation practices and
the risk varies considerably by the type of health inadequate precautions for cough-inducing proce-
care facility, the prevalence of TB in the community, dures, and lack of adequate respiratory protection.
the patient population served, the HCW’s occupa- Analysis of data collected from three of the health
tional group, the area of the health care facility in care facilities involved in the outbreaks indicates
which the HCW works, and the effectiveness of TB that transmission of M. tuberculosis decreased signifi-
infection-control interventions. The risk may be cantly or ceased entirely in areas where measures
higher in areas where patients with TB are pro- similar to those in the 1990 TB Guidelines were
vided care before diagnosis and initiation of TB implemented (2,29-32). However, several interven-
treatment and isolation precautions (e.g., in clinic tions were implemented simultaneously, and the ef-
waiting areas and emergency departments) or fectiveness of the separate interventions could not be
where diagnostic or treatment procedures that determined.
stimulate coughing are performed. Nosocomial
transmission of M. tuberculosis has been associated References
with close contact with persons who have infectious
TB and with the performance of certain procedures 2. CDC. Guidelines for preventing the transmission of
(e.g., bronchoscopy [17], endotracheal intubation tuberculosis in health care settings, with special focus
and suctioning [18], open abscess irrigation [20], 5. on HIV-related issues. MMWR 1990;39(No. RR-17).
CDC. Screening for tuberculosis and tuberculous in-
and autopsy [21,22]). Sputum induction and aero- fection in high-risk populations, and the use of pre-
sol treatments that induce coughing may also in- ventive therapy for tuberculous infection in the
crease the potential for transmission of M. tuberculo- United States: recommendations of the Advisory
sis (23,24). Personnel of health care facilities should Committee for Elimination of Tuberculosis. MMWR
be particularly alert to the need for preventing 1990;39(No. RR-8).

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