T-Spot.TB outperforms tuberculin skin test in predicting tuberculosis disease

Silicosis is a well-recognized risk factor for tuberculosis (TB).

To compare T-Spot.TB with tuberculin skin test (TST) in predicting the development of TB.

Male patients with silicosis without clinical suspicion of active TB, past history of TB, and treatment for latent TB infection (LTBI) were offered both T-Spot.TB and TST in the Pneumoconiosis Clinic of Hong Kong from 2004 to 2008, and followed prospectively until September 30, 2009, for development of TB.

Active TB and culture- or histology-confirmed TB developed in 17 (5.5%) and 14 (4.5%) of 308 recruited subjects at an annual rate of 2,247 and 1,851 per 100,000 person-years, respectively. Active TB occurred in 7.4% (15 of 204) and 1.9% (2 of 104) of T-Spot.TB-positive and -negative subjects, respectively, whereas the corresponding figures for TST (cutoff 10 mm) were 6.4% (13 of 203) and 3.9% (4 of 205), respectively. A positive T-Spot.TB test significantly predicted the subsequent development of active TB (relative risk, 4.50; 95% confidence interval, 1.03-19.68) and culture- or histology-confirmed TB (relative risk, 7.80; 95% confidence interval, 1.02-59.63). Consistent results were obtained after exclusion of subjects treated for LTBI and adjustment for potential confounders. TST did not significantly predict the development of active TB or culture- or histology-confirmed TB, irrespective of the cutoff values with or without exclusion of subjects treated for LTBI. Culture filtrate protein 10 spot count, but not early secretary antigenic target 6 spot count, was significantly associated with subsequent TB development.

T-Spot.TB performs better than TST in the targeted screening of LTBI among patients with silicosis.