Tuberculosis (TB) is a disease of significant public health burden affecting approximately 9 million people globally in 2013. The lack of a gold standard test to diagnose latent tuberculosis infection (LTBI), prior to development of disease, is a significant barrier to accurately measure the burden of TB. In 2011–2012, a TB component of the National Health and Nutrition Examination Survey tested for the presence of LTBI in a representative sample of the U.S. population using two different tests.
Civilian, noninstitutionalized U.S. population survey participants aged 6 years and older were given both the tuberculin skin test (TST) and QuantiFERON-TB Gold in Tube (QFT-GIT) blood test. Prevalence and numbers of TST positive (10 mm or greater), QFT positive (cutoff values used by NHANES), and both TST and QFT positive were calculated by adjusting for the complex survey design after applying corrections for item nonresponse and digit preference in TST induration measurements.
Of 9,756 survey participants, 6,064 (77.5%) had valid TST and QFT results available. Based on TST results alone, an estimated prevalence of 4.7% (95% CI 3.4–6.3) of the civilian, noninstitutionalized U.S. population aged 6 years or older, or 13,163,000 persons, had LTBI in 2011-2012. Results using QFT alone indicated a prevalence of 5.0% (4.2–5.8) or approximately 13,982,000 infections. Applying a definition of LTBI that required both TST and QFT positivity yielded a prevalence of 2.1% (1.5-2.8) or approximately 5,790,000 infected persons.
Defining LTBI infection using QFT alone resulted in a slight increase compared with TST overall. However, incorporating QFT and TST into the definition for LTBI reduced the prevalence estimate by more than half. The double positive results represent a more conservative definition of LTBI than either test result alone and would indicate a substantially lower TB infection prevalence rate based on TST or QFT positivity alone.
R. Miramontes, None