Nosocomial Mycobacterium Tuberculosis Outbreaks: Risk Factors, Prevention Intervention Efficacy, and Guidelines

Abstract

Mycobacterium tuberculosis can be transmitted to patients (nosocomial or hospital-acquired infection) or to health care workers (occupational-acquisition) in health care facilities. Before the 1980s, reports of nosocomial M. tuberculosis transmission were rare (1–3). The lack of reports of nosocomial patient to patient M. tuberculosis transmission in health care facilities can be related to the fact that only approximately 5–10% of immunocompetent persons exposed to a patient with infectious tuberculosis (TB) will develop TB in their lifetime; if an immunocompetent patient were exposed to an infectious TB patient in the hospital, development of infection and then active disease would occur months to years after the hospital exposure and nosocomial acquisition would never be considered. Thus, unless there is a cluster of patients with newly diagnosed TB or patients infected with a M. tuberculosis strain with an unusual antimicrobial resistance pattern, nosocomial M. tuberculosis transmission might not be suspected or detected. Thus, although rarely reported, nosocomial transmission of M tuberculosis can occur and remain undetected. In contrast, occupational acquisition has been documented as a risk to health care workers in the United States since the early 1930s. From 1935 through 1939, Israel followed a cohort of 637 nursing students during their hospital training (4). At entry into the study, 360 (57%) nurses were tuberculin skin test (TST) negative and 277 (43%) were TST positive. All of the TST-negative nurses had TST conversions during their training. Of the 637 nursing students, 68 (11%) developed active tuberculosis. Subsequent studies in the 1930s and 1940s also documented high (79–85%) TST conversion rates among nurses (5,6). During the 1940s and 1950s, studies were conducted showing that the risk of active TB among medical school students was over three times higher than the general population (7). Risk factors for disease among the medical students included exposure to unrecognized TB patients, the men’s TB ward, or presence in the autopsy room.