Comparison of interferon-γ release assay and tuberculin skin test using two cut-off points of to detect latent Mycobacterium tuberculosis infection in primary health care workers in Brazil

Souza, Fernanda

Comparison of interferon-γ release assay and tuberculin skin test using two cut-off points of to detect latent Mycobacterium tuberculosis infection in primary health care workers in Brazil

Wednesday, 20 August 2014

Exhibit hall (Dena'ina Center)

Fernanda M Souza, BS , Federal University Espirito Santo, Vitoria, Brazil

Thiago N do Prado, MS , Federal University of Espirito Santo, Vitoria, Brazil

Jair Pinheiro, MS , Municipality of Manaus, Amazonas, Brazil., Manaus/Amazonas, Brazil

Renata L Nobrega, MS , Federal University of Espirito Santo, Vitoria-ES, Brazil, Vitoria/ES, Brazil

Thamy C Lacerda, MS , Federal University of Espirito Santo, Vitoria/ES, Brazil

Rafaela B Loureiro, MS , Rio de Janeiro State University, Rio de Janeiro, Brazil

Geisa Fregona, MS , Federal University of Espirito Santo, Vitoria/ES, Brazil

Rodrigo R Rodrigues, PhD , Federal University of Espirito Santo, Vitoria/ES, Brazil

Lee W Riley, PhD , University of California, Berkeley, CA

Ethel L Noia Maciel, PhD , Federal University of Espirito Santo, Vitoria, Brazil

INTRODUCTION: A new interferon-γ release assay, QuantiFERON-TB Gold in tube (QFT) test, poses as an alternative test for the diagnosis of latent Mycobacterium tuberculosis infection (LTBI). Here, we compared the performance of QFT with tuberculin skin test (TST) measured at two different cut-off points among primary health care work (HCW) in Brazil.

METHODS: A cross-sectional study was carried out among HCW in four Brazilian cities with a known history of high incidence of TB. Results of the QFT were compared to TST results based on both >5mm and >10 mm as cut-off points.

RESULTS: We enrolled 632 HCWs. When the cut-off value of ≥10 mm was used, agreement between QFT and TST was 69% (k=0.31), and when the cut-off of ≥5 mm was chosen, the agreement dropped to 57% (k=0.22). The observed discordance between the QFT and TST results was significant by McNemar´s test for both cut-off points (p<0.001). We investigated possible factors of discordance of TST vs QFT (TST+/QFT- and TST-/QFT+) observed at either cut-off points. Compared to the TST-/QFT– group, risk factors for discordance at the TST+/QFT- group when the TST cut-off of ≥5 mm was considered were age between 41-45 [OR=2.70; CI 95%: 1.32-5.51] and 46-64 [OR=2.04; CI 95%: 1.05-3.93], BCG scar [OR=2.72; CI 95%: 1.40-5.25], and having worked only in primary health care [OR=2.30; CI 95%: 1.09-4.86]. On the other hand, when the cut-off value of ≥10 mm was used BCG scar [OR=2.26; CI 95%: 1.03-4.91], being a household contact of a TB patient [OR=1.72; CI 95%: 1.01-2.92] and having had a previous TST [OR=1.66; CI 95%: 1.05-2.62], were significant. Interestingly, discordance observed at the TST-/QFT+ group showed no statistically significant association with any of the variables regardless of TST cut-off value used.

CONCLUSIONS: Although we identified BCG vaccination to contribute to the discordance in spite of TST cut-offs, the current Brazilians recommendation for the initiation of LTBI treatment, based on TST, should not be changed, based on QFT limitations and decreased accuracy of the method.