Pseudoepidemics of Tuberculin Skin Test Conversions in the U.S. Army after Recent Deployments

Abstract

Rationale: The tuberculin skin test (TST) has many sources of error. These can lead to predominantly false-positive reactions when used in low-risk populations. The U.S. Army deploys to areas considered at highrisk fortuberculosis(TB)infection,butoftenhaslimitedcon- tact with the local population. Objectives: We describe the investigation of eight pseudoepidemics of TST conversions in U.S. Army populations, five of which were associated with overseas deployments. Methods: Outbreak investigations of these pseudoepidemics con- sisted of several components: evaluation of active and latent TB surveillancedata,reviewofmedicalrecords,investigationandinter- views of active TB cases and their contacts, evaluation of materials and personnel screening procedures, and placement and reading of repeat skin testing. MeasurementsandMainResults:Initiallyreportedriskofconversionin the outbreaks ranged from 1.3 to 15%. Repeat testing of converters (positives) found that 30 to 100% were negative on retesting. Sev- eral sources of false-positiveresults were identified in these pseudo- epidemics,includingvariabilityinreadingandadministration,prod- uct variability, and cross-reactions to nontuberculous mycobacteria. Conclusions: Pseudoepidemics of TST conversions are a common occurrence after U.S. Army deployments and in U.S. Army popula- tions. U.S. Army forces generally have a low risk of TB infection resulting from deployments due to limited exposure to local nation- als with active TB, and universal testing in this population has a low positive-predictive value.