Systematic review and meta-analysis of TST conversion risk in deployed military and long-term civilian travelers

Background. Transmission of tuberculosis (TB) during travel is a significant potential infectious disease threat to travelers. However, there is uncertainty in the travel medicine community regarding the evidence base for both estimates of risk for latent TB infection (LTBI) in long-term travelers and for information regarding which travelers may benefit from pre- or post-travel TB screening. The purpose of this study was to determine the risk for tuberculin skin test (TST) conversion, used as a surrogate for LTBI, in long-term travelers from low- to high-risk countries. Methods. We performed a systematic review to acquire all published and unpublished data on TST conversion in long-term civilian and military travelers from 1990 to June 2008. Point estimates and confidence intervals (CIs) of the incidence of TST conversion were combined in a random effects model and assessed for heterogeneity. Results. The cumulative risk with CI for LTBI as measured by TST conversion was 2.0% (99% CI: 1.6%-2.4%). There was a marked heterogeneity (χ² heterogeneity statistic, p < 0.0001) which could not be explained by evaluable study characteristics. When stratifying by military and civilian studies, the cumulative risk estimate was 2.0% (99% CI: 1.6-2.4) for military and 2.3% (99% CI: 2.1-2.5) for civilian studies. Conclusion. The overall cumulative incidence of 2.0% is what could be expected to occur among the local population in many developing-country settings, though TST conversion likely overestimates the risk of TB infection because of the low positive predictive value (PPV) of the TST in low-prevalence populations such as travelers. To maximize the PPV of a screening test for LTBI, a targeted testing strategy for long-term military and civilian travelers is recommended, based on exposures known to increase the risk of TB. Studies to better define higher risk groups, activities, and locations are needed.