Nosocomial tuberculosis.
Hospital employees are at risk of contracting tuberculosis from patients. The undiagnosed case with sputum-smear positive for acid-fast bacilli is the usual source case. However, even the smear-negative patient may pose a risk. This was documented by a high rate of skin test conversion in hospital staff exposed to a smear-negative, culture-positive patient in a respiratory intensive care unit. The patient required bronchoscopy, intubation, and assisted ventilation. Of susceptible hospital staff members who were exposed to the index case, 14 of 45 (31%) converted their PPD skin test. Ten of 13 (77%) susceptible hospital staff members present at the time of bronchoscopy converted, compared with 4 of 32 (12.5%) who were not present at bronchoscopy (Fischer's exact test p = 0.0006). Rough calculations suggest that during the bronchoscopy and intubation the index case generated at least 249 infectious units per hour. At the ventilation levels in this area, this resulted in 1 infectious unit of tuberculosis in each 68.9 cubic feet of air. Improved ventilation, high efficiency filters, and ultraviolet irradiation are effective recommended ways to clean the air of infectious  particles.
D000391:Air Microbiology; D003428:Cross Infection / Q000635:transmission*; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D012882:Skin Tests; D013242:Sterilization; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis / Q000635:transmission*