However, the terms "long periods of time" and "prolonged time" sharing the air exhaled by an infectious person are subjective. There is one report of a 150-minute intubation and bronchoscopy where 10 of 13 susceptible occupants of an intensive care unit became infected (36). In another case, 27 new infections resulted among 67 susceptible office workers who were exposed for 160 hours to the air exhaled by an infectious office worker in the same building (29). Additionally, Bloom and Murray noted that (30):
...epidemiological findings support the likelihood that the majority of patients infected with TB have acquired infection from nonintimate contacts.
B. Health-Care-Facility Workers' Potential for Exposure to Tuberculosis—Clinical procedures that can result in high concentrations of aerosolized droplet nuclei include bronchoscopy, administering aerosolized drug treatments, autopsy, and physical therapies to the chest that induce coughing (10). Rapid transmission (e.g., several hours) to health-care-facility workers has been linked to proximity with patients with infectious tuberculosis during use of aerosolized pentamidine (37), intubation and suctioning with mechanical ventilation (38), prolonged intubation (39), bronchoscopy followed by emergency intubation (40), openabscess irrigation (41), and autopsy (42,43). Other specific clinical or laboratory procedures that produce droplet nuclei include the manipulation of lesions or processing of tissue or secretions containing tuberculosis bacilli.
U.S. Public Health Service guidelines for biosafety in microbiological and biomedical laboratories state in part (44):
Mycobacterium tuberculosis and M. bovis infections are a proven hazard to laboratory personnel as well as to others who may be exposed to infectious aerosols in the laboratory...
Biosafety Level 3 practices, containment equipment, and facilities... are recommended for activities involving the propagation and manipulation of cultures of M. tuberculosis or M. bovis and for animal studies utilizing nonhuman primates experimentally or naturally infected with M. tuberculosis or M. bovis.
