221. Diagnostic Utility of Xpert MTB RIF in Extra-pulmonary Tuberculosis.
Session: Poster Abstract Session: Diagnostics: Mycobacteriology
Thursday, October 27, 2016
Room: Poster Hall
Posters
  • Xpert_Poster_v3.png (1.3 MB)
  • Background:

    Most studies of Xpert MTB RIF in EPTB (extra-pulmonary tuberculosis) have used culture as the comparative gold standard, but culture may be negative in most patients with EPTB. We evaluated the test against a composite reference standard (CRS) for diagnosis of TB composed of smear microscopy, mycobacterial culture, clinical findings, histology/cytology, site-specific imaging and response after 3 months of anti-tuberculous therapy (ATT).

    Methods:

    Retrospective study between January and June 2015. Patients above 18 years of age with suspected EPTB tested with site specific Xpert MTB RIF.

    Results:

    625 patients were tested for EPTB with Xpert MTB RIF during the study period. Of these,431 patients were excluded (283- alternate diagnoses, 84- missing medical records, 64- no follow up). 194 patients diagnosed with confirmed /probable TB were analysed. 22 of the 194 patients (11.3%) had received ATT before evaluation.

    Table 1: Sensitivity of smear, culture and Xpert MTB RIF

    Sample

    Smear +

    Culture +

    Xpert +

    Body fluids (33)

    0/33 (0%)

    8/33 (24.2%)

    8/33 (24.2%)

    Pus (24)

    3/20 (15%)

    12/20 (60%)

    23/24 (95.8%)

    CSF (14)

    0/14 (0%)

    2 /12 (16 .7%)

    7/14 (50%)

    Tissue (123)

    16/119 (13.4%)

    37/107 (34.6%)

    104/123 (84.6%)

    Total (194)

    19 /186 (10.2%)

    59/172 (34.3%)

    142/194 (73.2%)

     

    Table 2: Sensitivity of Xpert MTB RIF according to culture negative and culture positive status

    Xpert +

    Fluid

    Pus

    CSF

    Tissue

    Total

    Culture negative

    2/25

    (8%)

    12/12

    (100%)

    5/12

    (41.7%)

    68/86 (79.1%)

    87/135

    (64.4%)

    Culture positive

    6/8

    (75%)

    11/12

    (91.7%)

    2/2

    (100%)

    36/37

    (97.3%)

    55/59

    (93.2%)

    Total

    8/33

    (24.2%)

    23/24

    (95.8%)

    7/14

    (50%)

    104/123

    (84.6%)

    142/194

    (73.2%)

    Mean time to culture positivity was 18.2 days (5-36 days). Rifampicin resistance (RIF R) was detected by Xpert MTB RIF in 8 cases, of which 1 case was sensitive on phenotypic drug susceptibility testing (DST). RIF R was indeterminate in 1 case. Phenotypic DST was done in 30 of the 59 culture positive cases (50.8%). Concordance with DST was seen in 29 cases (96.7%) and discordance in 1(3.3%).

    Conclusion:

    Except for body fluids, Xpert MTB RIF was more sensitive than smears and cultures in all EPTB specimens including CSF, when a composite reference standard for TB was used. Xpert MTB helped to confirm the diagnosis in 64.4% of culture negative EPTB.These findings support WHO guidelines recommending the routine use of Xpert MTB in the diagnosis of EPTB.

    Vidya Krishna, MD, Fellow in training in Infectious Diseases1,2, Ram Gopalakrishnan, AB (Infectious Diseases), FIDSA1, Anil Tarigopula, MD (Path)3, P Senthur Nambi, FNB ID1 and V Ramasubramanian, MD, MRCP1, (1)Infectious Diseases, Apollo Hospitals, Chennai, India, (2)Pediatrics, Sri Ramachandra Medical College and hospital, Chennai, India, (3)Molecular Diagnostics Laboratory, Apollo Hospitals, Chennai, India

    Disclosures:

    V. Krishna, None

    R. Gopalakrishnan, None

    A. Tarigopula, None

    P. Senthur Nambi, None

    V. Ramasubramanian, None

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