High rates of latent TB infection in contacts and the wider community in South India.

BACKGROUND

We aimed to compare TB transmission rates between case and community households in Vellore, South India.

METHODS

359 household contacts (HHC) and 363 community contacts (CC) were assessed with tuberculin skin test (TST) and QuantiFERON TB Gold In-Tube test (QFT) between August 2010 and September 2011. Concordance test and multivariate risk factor assessment were conducted using logistic regression adjusted for clustering.

RESULTS

Latent TB infection (LTBI) positivity was similar between the two groups using both tests, with only moderate concordance observed between QFT and TST. Children of HHC (<15 years) were at a higher risk for LTBI (odds of 2.37 [1.15-4.89] and 3.02 [1.22-7.45] for TST and QFT respectively). Among adults, both age in decades (odds of 1.33 [1.14-1.15] and 1.16 [1.02-1.32] for TST and QFT, respectively) and the interaction of male gender, smoking and alcohol consumption (odds of 4.06 [1.38-11.93] and 2.59 [1.19-5.64] for TST and QFT, respectively), were associated with increased risk of LTBI.

CONCLUSIONS

This study provides estimates of TB infection rates accounting for both community and household exposure that contribute to understanding of TB transmission in this setting. We suggest that assessment of risk factors for infection need increased examination as prophylactic treatment of LTBI are being considered.