[Contact investigation using QuantiFERON-TB Gold test to evaluate TB exposure in 61 subjects in a hospital setting--(1) Outline of the outbreak and its clinical picture].

The index case was a patient who was admitted to a general hospital and treated with pulsed corticosteroid therapy; her breathing was assisted by a respirator. Soon she developed tuberculosis (TB) and died. Immediately after her death, QuantiFERON-TB Gold (QFT) test was conducted in healthcare workers who were in close contact with the index case. From the results of the test, all the healthworkers except 1 were TB negative. However, the QFT test repeated in the healthworkers after 8 weeks was positive in 18.6%. Subsequently, 5 healthworkers, including a doctor, nurses, and radiology technicians, developed TB. Bacterial isolates from 3 of them showed restriction fragment length polymorphism (RFLP) patterns similar to that of the index case. These 3 secondary TB cases included one healthworker who was in contact with the index case for less than 5 min, another whose QFT was negative (or "doubtful" according to the Japanese criterion of the QFT), and a third who was TB positive for QFT test but declined treatment for latent TB infection (LTBI). No other healthworkers or hospitalized patients developed TB. These healthcare workers with TB were further assessed using the QFT test at 6, 9, and 12 months after initial exposure, which showed an additional 4 positive reactors and 4 "doubtful" reactors who were indicated for LTBI treatment. Among these subjects, 7 were those who showed TB positive results 6 months after initial contact. Discussions were made on TB prevention in hospital settings including contact investigations the staff with special reference to application of the QFT test.