[Results of repeated QFT-2G checkings at two-year interval and their comparison with TST results introduced into infection control program for staffs working at a hospital with isolation wards for tuberculosis].

OBJECTIVE

In Fukujuji Hospital, we have been conducting TST to tuberculosis (TB) non-infected staffs to find new latent TB Infection (LTBI) every year, although almost of them were BCG vaccinated, and the reliability of TST is controversial in BCG vaccinated group. Recently, a new technique, QFT-2G, is evaluated highly to detect TB infection, especially in BCG vaccinated individuals. We examined hospital staffs twice at two-year interval using QFT-2G and TST, and compared these data.

MATERIAL & METHOD: About four hundreds fifty staffs in Fukujuji Hospital with isolation wards for tuberculosis, provided with high level program against nosocomial infection of TB were examined. Almost all of them were BCG vaccinated. Because one fifth to one seventh of them were supposed as TB non-infected, they had been examined with TST to find new LTBI every year. QFT-2G was applied for about 80-85% of staffs twice, 2003 Jan. and 2005 Jan., with each person's consent. We compared the sequential changes of TST reactions and QFT-2G data.

RESULTS

(1) The positive rate of QFT-2G was approximately 10% in both two-year interval checkings. (2) Two hundreds twelve persons, about half of staffs, were sequentially checked QFT-2G twice at two-year interval. 19 persons were positive at both checkings, 4 converted to negative and 7 converted to positive, suggesting that the rate of new LTBI in staffs would be 3.7% [7/(212-19-4)] during 2 years, 1.85% per year by QFT-2G conversion. (3) In comparison with data between TST and QFT-2G, QFT-2G was positive only in 13% of staffs with strongly reactors to TST. Moreover, even in 13 staffs converted by TST reaction to strong positive and highly suspected of new LTBI at two-year interval, there were no positive and positive converted persons based on QFT-2G checkings. Lastly, out of 7 staffs who converted to positive by QFT-2G checkings, only one was tested with TST, and no increase in the intensity of TST was observed.

CONCLUSION

The QFT-2G positive rate was about 10% and the new TB infection rate was estimated to be 1.85% par year in staffs of a hospital with TB wards provided with high level programs against nosocomial TB infection. In addition, there are apparent disagreements between the results of QFT-2G and TST reactions, presumably affected by prior BCG vaccination. Therefore we must be cautious to detect new LTBI by ordinary TST in BCG vaccinated group.