Comparison of the QuantiFERON-TB Gold In-Tube test with the tuberculin skin test for detecting latent tuberculosis infection in hemodialysis patients.

BACKGROUND AND OBJECTIVES: Hemodialysis (HD) patients are at increased risk of reactivation of latent tuberculosis (TB) infection (LTBI). LTBI screening of this population is recommended. The QuantiFERON-TB Gold assay (QFT-G) may be more accurate than the tuberculin skin test (TST) in the detection of LTBI. We prospectively compared the results of QFT-G to TST in HD patients. METHODS: We examined 100 patients and performed TST and QFT-G tests. Data obtained from patients and medical records included medical history (past history of TB, Bacillus Calmette-Guerin [BCG] vaccination, history of contact with previous TB cases), radiography reports (chest x-ray with changes consistent with old TB), and basic laboratory findings. RESULTS: Forty-three of 100 patients (43%) had a positive QFT-G test result and 34 (34%) had a positive TST test result. Overall agreement between the QFT-G and the TST was 65% (concordance [k]=0.26, P=0.01). Discordant test results were seen in 13 TST-positive/QFT-G-negative patients and in 22 TST-negative/QFT-G-positive patients. Before BCG vaccination and radiographic reports (of old TB changes) were associated with discordant test results. On multivariate analysis, a positive QFT-G test was associated with contact with previous TB cases (P=0.026) and radiographic report (P=0.034), whereas a positive TST test also was associated with a history of BCG vaccination (P=0.015). CONCLUSIONS: QFT-G test results were more closely associated with TB risk factors than were positive TST results. Additionally, the QFT-G test was not affected by BCG vaccination. We concluded that QFT-G test is a more useful diagnostic method than TST for detecting LTBI in HD patients.

Prevalence of Beijing genotype Mycobacterium tuberculosis strains in Istanbul.

To determine the prevalence of Beijing genotype Mycobacterium tuberculosis in Istanbul, 4069 strains were subjected to DNA fingerprinting. This is the first study to reveal the presence of the Beijing genotype in Istanbul. The prevalence rate was estimated as 1.13%, and it was shown that these strains were carried over from countries of the former Soviet Union. The study also showed that the prevalence of the Beijing genotype among at least rifampicin (RMP) resistant strains was significantly higher (2.7%) than among RMP-susceptible strains (0.9%).

Reliability of cord formation in BACTEC 12B/13A media for presumptive identification of Mycobacterium tuberculosis complex in laboratories with a high prevalence of Mycobacterium tuberculosis.

A total of 1208 positive BACTEC vials were examined for the presence or absence of serpentine cording. A very high (92.9%) rate of laboratory prevalence was obtained for Mycobacterium tuberculosis complex. The sensitivity, specificity, positive and negative predictive values of this test were 92.7%, 95.3%, 99.6% and 50.0%, respectively. It was concluded that testing cord formation in laboratories that have a high prevalence of Mycobacterium tuberculosis complex is an exceptionally reliable method for preliminary reporting of cording-positive cases; however, for cording-negative cases, preliminary reports based solely on cord formation are not reliable. It was also observed that the length of the incubation period has a significant effect on cord formation. Incubation periods of 4 days or less are not sufficient to determine noncording in smears prepared from positive BACTEC vials.