Case-Control study of Firefighters with documented positive tuberculin skin test results using Quantiferon-TB testing in comparison with Firefighters with negative tuberculin skin test results

Background: Phoenix Firefighters have had abnormally high rates of tuberculin skin test (TBST) results on medical surveillance. The objectives of this study were to evaluate our firefighters using QuantiFERON-TB (QFT), comparing the results to their TBST results. Methods: Using QFT results obtained during the study, we compared previously positive TBST responders (Cases) to negative responders (Controls). We also compared both groups for QFT results for Mycobacterium avium (MA) exposure. Results: QFT effectively monitored our working population. 12.9% of the 148 cases, and 3.2% of the 220 controls had a positive QFT result. Another 14.8% of cases and 4.5% of controls had conditionally positive QFT results. There was an unusually high rate of MA response on QFT testing in both groups. Conclusion: Phoenix Firefighters have a higher than expected TBST and QFT results, which cannot be explained by the increased MA rate. The decreased level of QFT positivity in comparison to TBST results may indicate a considerable false positive TBST rate. The QFT offers many advantages as a surveillance method over TBST in exposed worker populations.