Japan - extended contact study further validates QFT

No reported problems with TST boosting, BCG innoculation and youth and QFT showed excellent predictive value;

none of the 297 students who were QFT-G negative had developed active TB after 3 years of follow-up

According to JATA (Kekkaku October 2004) the new TB law has dropped BCG innoculation of school kids in favour of BCG vaccination at birth;

the new Law will adopt the direct vaccination scheme in which babies will be given the BCG vaccine without tuberculin testing.

Importantly the market for using QFT in contact testing in Japan has now passed the "tipping point", contact tracing in Japan has been described as a "predominant market"

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Source

Contact investigation in a primary school using a whole blood interferon-gamma assay.

Higuchi K, Kondo S, Wada M, Hayashi S, Ootsuka G, Sakamoto N, Harada N.
The Research Institute of Tuberculosis, Japan Anti-Tuberculosis Association, Kiyose City, Tokyo, Japan.

OBJECTIVES: To evaluate the usefulness of QuantiFERON®-TB Gold (QFT-G) for children.

METHODS: Students in a primary school exposed to a tuberculosis patient were investigated using the tuberculin skin test (TST), chest X-ray examination and sequential QFT-G tests.

RESULTS: The first QFT-G test was conducted one month after the end of exposure for 308 of the 313 children, with 6 (1.9%) positive. TST results were obtained from 306 of the students at 2 months after exposure, and 200 (65.4%) had induration >/=5mm. A second QFT-G test, a further month later, and a third QFT-G test, six months after exposure, found an additional 2 positive and one weakly positive, respectively.

Overall, the rate of QFT-G positivity was 9.8% (4/41) for close contact children (≥90 h exposure), significantly higher than for casual contacts (≥18 h exposure; 1.8%, 5/272; p = 0.020), whereas there was no significant difference in TST positive rates (p = 0.078).

CONCLUSIONS: These data suggest that QFT-G has the same performance characteristics in BCG vaccinated children as it does in adults. The observation that none of the 297 students who were QFT-G negative had developed active TB after 3 years of follow-up suggests that QFT-G has a very high negative predictive value.