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

James L Fleming,Timothy L England,Howard B Wernick,Alicia Laduke,Patrick L Kelley,Steven Reinhart,Victor Papst,John A Dominguez,Forrest D Gorter

doi:10.1186/1745-6673-1-28

James L Fleming, Timothy L England + Show 7 more

Open Access

https://doi.org/10.1186/1745-6673-1-28

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Abstract

BackgroundPhoenix 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.MethodsUsing 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.ResultsQFT 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.ConclusionPhoenix 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.

Highlights

Phoenix Firefighters have had abnormally high rates of tuberculin skin test (TBST) results on medical surveillance
The techniques for intradermal injection, and potential variability in interpretation of test results can reduce the effectiveness in using TBST for medical surveillance
The aims of this study are to: 1) compare QFT results to TBST results in a population where a high incidence of positive latent tuberculosis infection (LTBI) results are present; and 2) determine if Mycobacterium avium (MA) is a confounder in TBST testing among our firefighters

Summary

Introduction

Phoenix Firefighters have had abnormally high rates of tuberculin skin test (TBST) results on medical surveillance. The level of nontuberculous mycobacterial infection rates within the community can affect specificity by increasing the proportion of false positives and influencing the positive predictive value [4]. For this reason TBST is considered positive at varying levels of localized reaction, depending on the likelihood of exposure[4]. Health care workers are classed in the group at increased risk where a TBST response of 10 mm would be considered a positive response This allows for more individuals to be covered, it leads to a higher incidence of false positive testing [5]

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