Assessment of nosocomial transmission of tuberculosis in a psychiatric hospital using a whole blood interferon-gamma assay

We conducted a contact investigation in a psychiatric hospital to evaluate the nosocomial transmission of tuberculosis (TB). Contacts included hospital healthcare workers (HCWs) and inpatients who had been exposed to an index case of pulmonary TB. Contacts were evaluated for Mycobacterium tuberculosis infection with standard screening methods as well as the QuantiFERON(R)-TB Gold (QFT-G) test. A tuberculin skin test (TST) was administered to 3 individuals who were under 30 years old, and all tests were negative. Chest X-ray examination was performed for all 46 contacts (9 HCWs and 37 patients). Five had abnormal chest X-ray results that were not compatible with TB, and 41 had normal chest X-rays. As regards the QFT-G test, 23 of the 46 (50%) contacts, 1 HCW (an 81 year-old male) and 22 patients, were positive. The results suggest that there was significant nosocomial transmission of TB infection among inpatients in this psychiatric hospital. Moreover, these findings indicate that the use of chest X-ray and TST, i.e., conventional methods of detection will leave TB infection undetected in many individuals. Thus, introduction of screening for TB infection using the QFT-G test in long-term care facilities such as psychiatric hospitals may enable the detection and treatment of individuals with latent TB in whom the infection would otherwise be missed by other conventional screening methods.