[Contact investigation using QuantiFERON-TB Gold test to evaluate TB exposure in 61 subjects in a hospital setting--(2) Change in QuantiFERON response during one year after exposure].

UNLABELLED: OBJECTIVES & SUBJECTS: The change in IGRA (interferon-gamma release assay, with QuantiFERON-TB Gold, QFT) responses was followed up for one year in a group of contacts of healthcare workers who had been exposed to tuberculosis (TB) infection for a relatively short period in a hospital. The observation was made of a total of 59 close contacts of the index case, where 16 showed positive QFT-conversion and 7 showed the intermediate response ranging 0.1 to 0.35 IU/mL. Three of the conversion cases developed active TB. RESULTS: 67% of the QFT conversions occurred within 2 months of exposure and the others between 2 to 9 months. Those having converted later than 2 months after the exposure showed generally weaker QFT responses than the earlier converters. In response to the treatment to converters (either to latent TB infection or to active TB), 80% of the cases reversed to negative or intermediate. The geometric means of the response values for ESAT-6 and CFP-10 also showed significant decline over the treatment time. DISCUSSIONS: The time profile of responses in the intermediate responders revealed an obviously distinct pattern from that of the negative responders with the values remaining uniformly at very low level throughout, which suggests that this group includes somehow exceptional responders either with or without infection.

[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.