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DOI: 10.1055/s-2006-934020
Avoiding the effect of BCG-vaccination by detecting MTB-infection with a new blood test
Methods: We compared the TST with a Mycobacterium tuberculosis (MTB)-specific ELISPOT-assay during an outbreak Results: Participants were grouped according to their risk of LTBI in close (n=36) or occasional (n=333) contacts to the index case. For the TST the positive response rate was 53% (19/36) among close and 16% (52/333) among occasional contacts. Fifty-six TST-positive contacts (56/71=78.9%) and 27 TST-negative controls (27/298=9.1%) underwent ELISPOT testing. The OR of a positive test result across the two groups was 29.2 (95% CI 3.5–245.0) for the ELISPOT and 19.7 (95% CI 2.0–190.2) for the TST with a 5mm cut-off. Of 369 contacts, 158 (42.8%) had previously received BCG-vaccination. The overall agreement between the TST and the ELISPOT was low (κ=0.16), and positive TST-reactions were confounded by BCG-vaccination [OR 4.8 (95% CI 1.3–18.0)]. In contrast, use of a 10-mm induration cut-off for the TST among occcasional contacts showed strong agreement between TST and ELISPOT in non-vaccinated persons (κ=0.61). In BCG-vaccinated individuals a MTB-specific ELISPOT-assay is a better indicator for the risk of LTBI than the TST.