[Epidemiological study on contact examinations done by Nishio Health Center using QFT from 2008 to 2010].

OBJECTIVE: To elucidate epidemiological significance of contact examination using QFT.

SUBJECTS AND METHODS: The subjects of this retrospective study were 110 TB patients registered at the Nishio Health Center between 2008 and 2010, and their contacts who were examined by Nishio HC using QFT in the same period. All registration files were reviewed to identify the index cases and their contacts examined with QFT. An index case, at least one of whose contacts was proven QFT-positive was considered as a source patient. An index case linked to a secondary TB patient whose QFT result was not positive was also considered as a source patient. A contact examination rate (CER) was defined as following; CER = NI/NA, where NA is Number of TB patients in a category A, and NI is Number of index cases in category A. A source patient rate (SPR) was defined as following; SPR = NS/NI, where NI: Number of index cases in a category A, and NS: Number of source patients in category A. A QFT positive rate (QPR) was defined as following; QPR = NQP/NC, where NQP: Number of QFT-positive contacts in a category A, and NC: Number of the contacts in category A.

RESULTS: A total of 110 TB patients were registered at the Nishio Health Center between 2008 and 2010. Pulmonary TB was found in 79 patients, and 31 had extra-pulmonary TB. Of the 79 patients with pulmonary TB, 37 were smear-positive, 32 were smear-negative but positive for culture or a nucleic acid amplification test, and 10 were bacteriologically negative. The numbers of index cases in these patients according to the bacteriological categories were 23, 2 and none, and the CERs were 62.2%, 6.3%, and 0%, respectively. There were 7 source patients with QFT-positive contacts. Another source patient was associated with a secondary patient who was QFT-negative and diagnosed with tuberculous pleurisy 10 months after the contact. All of these 8 source patients were smear-positive. The SPR was 34.8% for the 23 smear-positive index cases. The ages of the 37 smear-positive patients were 40 to 64 in 15 patients, and 65 or more in 22. 12 of them were female and 25 male. The CERs were 66.7%, for those aged 49 to 64 years, 59.1% for 65 years or older, 75.0% for females, and 56.0% for males. The SPRs were 50.0%, 23.1%, 22.2%, and 42.9%, respectively. Two smear-negative and bacteriologocially positive index cases were associated with two QFT-negative contacts. A total of 113 contacts from 22 smear-positive index cases were examined with QFT from 2008 to 2010. The contacts of a smear-positive index case registered late December, 2010 were excluded, since the examination was done in 2011. There were 17 contacts with positive QFT, and the QPR was 15.0%. Of the 7 index cases, one case had 7 QFT-positive contacts, two had 3 QFT-positive contacts, and each of remaining 4 cases had a single QFT-positive contact. The QPRs were 9.1% for 11 contacts aged 10-19 years, 17.2% for 29 twenties, 10.3% for 29 thirties, and 16.2% for 37 forties. In addition to the 113 contacts, 77 contacts of 8 smear-positive index cases were examined with QFT during the same period. Out of these 8 index cases, 3 were registered in 2005 and 2007, and the other 5 were registered at other Health Centers, but they had social activities in the Nishio HC's service area being in contact with 70 persons in the Nishio area.

DISCUSSION: The contact examinations are heterogeneous in nature, with cases registered before or after the study period, and with contacts of index cases registered at other Health Centers. Both of them could not be the subjects for the CER calculation, since these contacts are related to the index cases not belonging to the defined case population.

CONCLUSION: These findings suggest that the CERs for the male TB patients are lower than those for the female, the SPRs for the male and middle-aged TB patients are higher than those for the elder and the female, and that the CERs and the QPRs are useful parameter to monitor the results of contact examination using QFT.