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Targeted Testing for Latent TB
Use of a simple four-variable risk-factor questionnaire could have reduced testing by 91%.
In the U.S., testing for latent tuberculosis infection (LTBI) is currently recommended only for individuals who are at high risk for infection, based on clinical factors. Such targeting greatly reduces the number of people tested and does not negatively affect disease control efforts. The U.S. military is still testing all recruits, even though the case rate of TB is far lower in recruits than that in the general U.S. population.
In a recent study involving Army recruits at Fort Jackson, South Carolina, researchers evaluated the accuracy of a risk-factor questionnaire (RFQ) in predicting a positive result on three currently available screening tests (the tuberculin skin test [TST] and 2 interferon- release assays: the QuantiFERON-TB Gold In-Tube [QFT-GIT] test and the T-SPOT.TB [T-Spot] test).
A total of 1783 recruits completed the study and had valid results (either positive or negative) on all three tests. Of these, 105 (5.9%) had a positive TST. A four-variable RFQ model, with a sensitivity of 79% and a specificity of 92% for predicting TST positivity, showed the best bias-variance trade-off. The variables included in this model were (1) close contact with a person who had active TB, (2) birth in a country with TB prevalence 20 per 100,000, (3) residence with a parent who was born outside the U.S., and (4) prior positive TST results. Only 166 participants (9%) were positive for any of the four variables; targeted testing of just those recruits would have reduced TB testing by 91%. The four-variable RFQ had a sensitivity of 41% and a specificity of 91% in predicting positive results on either the QFT-GIT or the T-Spot.
Impact of targeted testing for latent tuberculosis infection using commercially available diagnostics.
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