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Updated: Mar 20, 2026
Diagnosing Pulmonary Tuberculosis with the Xpert MTB/RIF Test
Published on: April 9, 2012
[USE OF QuantiFERON® TB-GOLD IN-TUBE IN A CONTACT INVESTIGATION TO DETERMINE THE ONSET OF TUBERCULOSIS WITH OR
Purpose:
QuantiFERON® TB-Gold In-Tube (3G) testing was performed on tuberculosis-positive index cases and their contacts. The purpose of this study was to evaluate the relationship between 3G test results and the subsequent development of tuberculosis, and to identify effective strategies to prevent the onset of tuberculosis.
Methods:
Index cases and their contacts were subjected to 3G testing in a contact investigation in Osaka City in 2011-2012. For index cases, sputum smears were tested, and the infecting organism was identified. For the contacts, the following information was collected: age, results of 3G testing, presence or absence of latent tuberculosis infection (LTBI) treatment, and onset of tuberculosis disease within 2 years of follow-up from the last contact with the index cases.
Results:
(1) There were 830 index cases, including 774 subjects with pulmonary tuberculosis (93.3%) and 3 with laryngeal tuberculosis (0.4%). From sputum smear tests, 726 patients (87.5%) were determined to be 3G positive, and 83 (10.0%) were determined to be 3G negative. (2) In total, 2,644 contacts were subjected to 3G testing. Of these, 2,072 patients (78.4%) tested negative, 196 (7.4%) showed an equivocal result, and 375 (14.2%) tested positive. Their mean ages were 33.7, 38.0, and 38.8 years, respectively, showing significant differences in tuberculosis status according to age (P < 0.001). (3) Among the 2,072 3G-negative contacts, tuberculosis developed in 2 (0.1%) of 2063. None of these contacts was treated for LTBI. Among the 375 3G-positive contacts, tuberculosis developed in 36 (36.0%) of 100 subjects that were not LTBI treated, while tuberculosis developed in 3 (1.1 %) of 275 subjects that were LTBI treated. A significant difference in the incidence of tuberculosis between treated and untreated 3G-positive contacts was observed (P < 0.001).
Discussion:
Tuberculosis developed in a high proportion of 3G-positive contacts that were not LTBI treated, suggesting the need for preventive management of 3G-positive contacts.
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