[Application and problems of quantiFERON TB-2G for tuberculosis control programs--(1) tuberculosis outbreak in a Cram...

The purpose of this study was to evaluate the usefulness of the QuantiFERON TB-2G (QFT), which is a novel method of detecting tuberculosis (TB) infection, in a case of TB outbreak.

The index case was a teacher of a cram school in which students received one-to-one lessons. Subjects of the contact investigation were 118 students, 28 teachers, and 47 guardians. At first tuberculin skin test (TST) and QFT were performed only on subjects under 40 years old, but subjects of QFT were extended to the other contacts later.

The QFT positive rates for students (70.0%) and teachers (56.5%) proved to be high according to the first contact investigation. Total of 46 secondary TB cases have been detected during the past 15 months after the index case had diagnosed as TB. The secondary attack rate for students, teachers, and guardians was 24.6%, 42.9%, and 8.3%, respectively. Ninety-three contacts, who were QFT positive or intermediate, or strong TST reactors, were indicated for chemoprophylaxis. The restriction fragment length polymorphism (RFLP) patterns of isolates from eight patients were identical to those of an isolate from the index case. Both infection and attack rates among students tended to increase in proportion to the degree of exposure and the frequency of attendance to the school. The youngest among students who developed TB disease was 13 years old and the attack rates were about 30 to 50 percent between 15 and 33 years old.

It was concluded that the QFT test was very useful for confirming the extent of transmission of TB and for motivating the candidates for chemoprophylaxis to accomplish treatment. However, the QFT test was not helpful for reducing the indication of chemoprophylaxis because the infection rates were very high in our case. Some epidemiological findings about the influence of age factor to the potential of progression to active TB in young people were obtained.