Non-tuberculous mycobacteria and the performance of interferon gamma release assays in Denmark.
BACKGROUND
The QuantiFERON-TB-Gold Test (QFT) is more specific than the Mantoux skin-test to discriminate between Mycobacterium tuberculosis (MTB) and non-tuberculous mycobacterial (NTM) infections. Here we study the performance of the QFT in patients with NTM disease.


METHODS
From 2005 to 2011, nationwide patient data on positive NTM cultures (n = 925) were combined with nationwide data on QFT results (n = 16,133), both retrieved from the International Reference Laboratory of Mycobacteriology, Denmark. A total of 112 patients with NTM infections had a QFT performed, 53 patients had definite NTM disease, 10 had possible disease and 49 had NTM colonization.


RESULTS
QFT was positive in 8% (4/53) of patients with definite disease, 40% (4/10) with possible disease and 31% (15/49) with colonization. Positivity rate was lowest among patients with definite disease infected with NTM without the RD1 region 4% (2/50). None of the 15 children with MAC lymphadenitis had a positive QFT.


CONCLUSIONS
This study is one of the largest assessing IGRAs in patients with NTM disease in a TB low-incidence setting. Our study showed that the QFT holds potential to discriminate between NTM and MTB infections. We found no positive IGRA test results among children with NTM not sharing the RD1-region of MTB resulting in a 100% specificity and we suggest that a QFT in a child presenting with cervical lymphadenitis may be helpful in distinguishing NTM from TB lymphadenitis.
Department of Thoracic Medicine and Infectious Disease, Nordsjaelland Hospital, Hillerød, Denmark; International Reference Laboratory of Mycobacteriology, Statens Serum Institut, Copenhagen, Denmark.
Thomas Stig
TS
Hermansen
International Reference Laboratory of Mycobacteriology, Statens Serum Institut, Copenhagen, Denmark.
Vibeke Østergaard
VØ
Thomsen
International Reference Laboratory of Mycobacteriology, Statens Serum Institut, Copenhagen, Denmark.
Troels
T
Lillebaek
Department of Thoracic Medicine and Infectious Disease, Nordsjaelland Hospital, Hillerød, Denmark.
Pernille
P
Ravn
D000328:Adult; D000368:Aged; D016208:Databases, Factual; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D059425:Interferon-gamma Release Tests; D008297:Male; D015201:Meta-Analysis as Topic; D008875:Middle Aged; D009165:Mycobacterium Infections, Nontuberculous / Q000175:diagnosis* / Q000453:epidemiology; D009170:Nontuberculous Mycobacteria / Q000276:immunology; D012042:Registries; D015203:Reproducibility of Results; D012189:Retrospective Studies