Abstract
We used the T-SPOT.TB assay in screening HIV positive contacts of infectious TB cases in the prison setting. The test is believed, on presumptive evidence, to be more sensitive than the tuberculin skin test and QuantiFERON-TB Gold In-Tube assay in detecting latent TB infection.
We report the screening of 47 HIV positive contacts around 3 infectious TB cases in the prison from 2008 to 2010. Exposure of the contacts occurred during the 1-hour daily activities. Identified contacts were screened for symptoms and examined for signs of active disease. Sputum tests for AFB smears and cultures, chest xray and T-TSPOT.TB assay were done. Diagnosis of latent TB infection was based on the T-TSPOT.TB assay, after excluding active disease. Window prophylaxis was offered if the initial test was negative and stopped if the repeat T-SPOT.TB assay done after 8-10 weeks of last exposure was negative.
36 (76.6%) the contacts were tested negative by the T-SPOT.TB assay. Their median CD 4 count was 343 cells/ul and 44.4% of them were on anti-retroviral therapy. 8 contacts had positive T-SPOT.TB assay result, 2 of whom had active TB (yield of 4.3%). The indeterminate rate was 2.1%. 3 contacts completed preventive treatment while 14 contacts had window prophylaxis. During the mean follow up of 19 months (median of 21.5 months, range of 10 to 25 months), one of the T-TSPOT.TB assay negative contacts, whose CD4 count was 4 cells/ul, developed active TB 11 months after completing screening.
Except in cases with extremely low CD4 count, the T-SPOT.TB assay appears to have a good negative predictive value for progression to active disease in HIV positive TB contacts in Singapore.
- © 2011 ERS
