Preventing the Nosocomial Transmission of Tuberculosis

The resurgence of tuberculosis in the United States since 1985 has been accompanied by an increasing number of reports of nosocomial transmission of tuberculosis (both drug-susceptible and drug-resistant strains) in hospitals, prisons, and shelters [1-15]. Inefficient infection control procedures have contributed to recent outbreaks of tuberculosis, as have increases in the number of patients coinfected with Mycobacterium tuberculosis and the human immunodeficiency virus (HIV) [5, 14]. In several outbreaks, transmission was facilitated because patients with unsuspected tuberculosis were clustered with susceptible immunocompromised patients (for example, in acquired immunodeficiency syndrome [AIDS] wards in large urban hospitals). In addition, recognition of tuberculosis in patients with HIV infection was delayed because atypical presentation and chest radiographic findings or low clinical suspicion led to misdiagnosis and failure to isolate patients with active pulmonary disease [5, 7, 8, 11, 12, 15-20]. Other factors included laboratory delays in identification and susceptibility testing of M. tuberculosis isolates and a failure to recognize the ongoing infectiousness of patients [5, 7, 12, 14]. These recent outbreaks emphasize the importance of effective tuberculosis infection control efforts in health care settings. In December 1990, the Centers for Disease Control and Prevention (CDC) issued guidelines for preventing transmission of tuberculosis in health care settings [13]; revised guidelines were issued in October 1994 [14]. A hierarchy of control measures (administrative, engineering, personal respiratory protective equipment [that is, respirator masks]) have been recommended by CDC to prevent nosocomial transmission of tuberculosis [14]. However, few data are available on the efficacy of these guidelines [16], and CDC has recognized the urgent need to assess the efficacy of isolation in preventing the transmission of tuberculosis [21]. The cost of implementing these recommendations is high [22], particularly for engineering requirements (for example, retrofitting rooms for respiratory isolation) and personal respiratory protective equipment. The Occupational Safety and Health Administration (OSHA) has mandated the use of high-efficiency particulate air (HEPA)-filtered respirator masks [23] as the minimum level of respiratory protection in U.S. health care institutions. These HEPA respirator masks are expensive; a disposable HEPA respirator costs more than $5 per mask, which is more than five times the cost of dust-mist respirators. The efficacy of these HEPA respirator masks compared with that of other types of respirators is unknown [23]. Resources for these expensive engineering and personal respiratory protective equipment mandates are especially difficult to obtain at inner-city public hospitals, which often care for many patients with tuberculosis. We studied the efficacy of expanded tuberculosis infection control measures (consisting primarily of administrative controls) that were implemented at Grady Memorial Hospital, Atlanta, Georgia, after documented transmission of drug-susceptible tuberculosis occurred on several wards of the hospital [10]. We evaluated two measures of health care worker occupational exposure to tuberculosis: 1) tuberculosis exposure episodes [that is, the number of patients with acid-fast bacilli smear-positive pulmonary tuberculosis not admitted into respiratory isolation at hospital admission] and 2) tuberculin skin test results of health care workers at our urban public hospital, which has limited resources and each year cares for more than 200 patients with laboratory-confirmed tuberculosis. Methods Tuberculosis Exposure We measured two aspects of health care worker exposure to tuberculosis before and during implementation of tuberculosis infection control measures at Grady Memorial Hospital, a public, university-affiliated, 1000-bed inner-city hospital in Atlanta, Georgia. We evaluated the number of tuberculosis exposure episodes between 1 July 1991 and 30 June 1994 and the tuberculin skin test conversion results of health care workers at Grady Memorial Hospital between 1 January 1992 and 30 June 1994. An episode of tuberculosis exposure was considered to occur when a patient not placed in respiratory isolation at hospital admission subsequently had a diagnosis of acid-fast bacilli smear-positive and culture-positive pulmonary tuberculosis (on the basis of isolation of M. tuberculosis from sputum or bronchoalveolar lavage fluid specimens) during that admission or within 2 weeks of discharge. Days of tuberculosis exposure were defined as the cumulative number of days that patients with acid-fast bacilli smear-positive, culture-positive pulmonary tuberculosis were not housed in respiratory isolation rooms. We began to prospectively follow tuberculosis exposure episodes on 1 March 1992, after an expanded respiratory isolation policy was implemented. We retrospectively determined the number of tuberculosis exposure episodes that occurred between 1 July 1991 and 29 February 1992 by reviewing laboratory records and patient charts. Acid-Fast Bacilli Smears and Cultures The hospital's clinical microbiology laboratory did acid-fast bacilli smears using a concentrated method and fluorochrome staining [24]; respiratory specimens were decontaminated by standard procedures [25]. Acid-fast bacilli cultures were done by inoculating specimens onto Middlebrook 7H11 agar (Becton Dickinson, Cockeysville, Maryland) and into radiometric broth media (Bactec, Becton Dickinson, Sparks, Maryland). Mycobacterium isolates were identified as M. tuberculosis complex by nucleic acid probes (Gen-Probe, San Diego, California). Tuberculin Skin Testing Tuberculin skin testing for health care workers was done at the hospital's Occupational Health Services Clinic using the Mantoux method; a 0.1-mL (5 tuberculin units) solution of purified protein derivative (Aplisol, Parke-Davis, Morris Plains, New Jersey, or Tubersol, Connaught, Swiftwater, Pennsylvania) was placed intradermally on the volar surface of the forearm and was read 48 to 72 hours later by a member of the Occupational Health Services staff (nurse, physician, or physician assistant). Self-reporting of results by health care workers was not permitted. A positive tuberculin skin test result was defined as an induration of at least 10 mm. A baseline tuberculin skin test was done when the health care worker began working at the hospital; results of this baseline testing were excluded from the analysis. Two-step tuberculin skin testing [14] for new health care workers was not done during the study period. Tuberculin skin testing has been mandatory for all Grady Memorial Hospital employees since 1976. Extremely high compliance (almost 100%) has been assured by the requirement of documentation of a recent tuberculin skin test result (or documentation of a previous positive tuberculin skin test result) before issuance and renewal of the hospital's identification badge, which must be worn by all health care workers. A tuberculin skin test conversion was defined as a documented positive test result following a documented negative result of a test done by the Occupational Health Services staff. We included all health care workers whose tuberculin skin tests were done by the Grady Occupational Health Services during the study period (that is, all Grady Memorial Hospital employees, Grady-based university physician faculty, and housestaff and medical and allied health students who were tested at the Grady Occupational Health Services). We did not include results of tuberculin skin testing of housestaff and students who rotate through Grady Memorial Hospital but who were tested at other sites (for example, at other Emory University-affiliated hospitals). Control Measures Expanded tuberculosis infection control measures were implemented at Grady Memorial Hospital after documented transmission of tuberculosis occurred on several wards in late 1991 and early 1992 [10]. The following are the control measures and the dates they were implemented. 1. Administrative controls. These controls consisted primarily of an expanded respiratory isolation policy that was implemented on 1 March 1992. The previous isolation policy required isolation of patients known or suspected to have tuberculosis; also, under this policy, respiratory isolation was discontinued after 2 weeks of antituberculous therapy. The new expanded respiratory isolation policy included mandatory isolation of all patients with active tuberculosis, those with tuberculosis that was established in the differential diagnosis (or when an acid-fast bacilli sputum smear and culture were ordered), and those with HIV infection (or patients at high risk for HIV infection if serologic status was unknown) who had an abnormal chest radiograph. Isolation could be discontinued only after three consecutive negative acid-fast bacilli sputum smears were obtained or when the patient was discharged from the hospital. Other new administrative controls included increased surveillance by the Epidemiology/Infection Control Department to ensure that all patients with acid-fast bacilli sputum smear and culture specimens received by the clinical microbiology laboratory were in respiratory isolation (1 March 1992); the hiring of a nurse epidemiologist to serve as tuberculosis infection control coordinator (1 July 1992); and expanded health care worker education about tuberculosis (1 March 1992), which accompanied implementation of the expanded respiratory isolation policy. This education was especially targeted to nursing staff, house staff, and attending physicians. The frequency of routine mandatory tuberculin skin testing was increased from yearly to every 6 months and was expanded to cover nonemployee health care workers (such as attending physicians, housestaff, and medical students) (July 1992). 2. Interim engineering contr