Performance of the Xpert MTB/RIF assay in the diagnosis of tuberculosis in formalin-fixed, paraffin-embedded tissues.
Extrapulmonary tuberculosis (EPTB), which accounts for 10%-40% of the global burden of TB, with the highest incidence in Sub-Saharan Africa, is strongly associated with human immunodeficiency virus infection. Diagnosing EPTB is challenging, and recently, there has been a concerted effort to evaluate the latest molecular diagnostics for diagnosing TB in a range of specimen types. The Xpert MTB/RIF assay (Cepheid, Sunnyvale, CA, USA) is one such technology, which simultaneously detects Mycobacterium tuberculosis and rifampicin resistance. Our objective was to evaluate the accuracy of the Xpert MTB/RIF assay for the diagnosis of EPTB and detection of rifampicin resistance in routinely processed formalin-fixed, paraffin-embedded (FFPE) tissues, compared with histological detection of TB as the gold standard.



A convenience set of 100 biobanked FFPE tissues, including lymph nodes (n = 64), male genital tract tissue (n = 10), abdominal tissue (n = 8), female genital tissue (n = 5), breast tissue (n = 5), synovial tissue (n = 4), skin (n = 2), tongue tissue (n = 1), and thyroid (n = 1), from routine cases of clinically suspected EPTB admitted to the University Teaching Hospital, Lusaka, Zambia, were analyzed using the Xpert MTB/RIF assay and in-house polymerase chain reaction (PCR) assay targeting IS6110, in parallel with Ziehl-Neelsen (ZN) staining, against histology as the gold standard.



Some 66% of specimens had histological evidence of TB infection. ZN staining was positive for TB in 8% of cases, and Xpert MTB/RIF was positive for TB in 25% of cases. Taking histology as the gold standard, the sensitivity and specificity were as follows: In lymph tissue the accuracy of the Xpert MTB/RIF assay was 41% (95%CI 27-57), not significantly better than ZN or the in-house PCR assay. In non-lymph tissue the sensitivity of the in-house PCR assay was 82% (95%CI: 56%-95%), significantly higher than the Xpert MTB/RIF assay (P = 0.004). The Xpert MTB/RIF assay indicated rifampicin resistance in just three cases.



The Xpert MTB/RIF assay is potentially a useful tool for the diagnosis of TB in routine FFPE tissues.
Department of Biomedical Sciences, University of School of Medicine, Lusaka, Zambia.
Pascal
P
Polepole
University of and University College London Medical School (UNZA-UCLMS) Research and Training Programme, University Teaching Hospital, Lusaka, Zambia.
Mwila
M
Kabwe
Department of Pathology and Microbiology, University Teaching Hospital, Lusaka, Zambia.
Mpanga
M
Kasonde
University of Zambia and University College London Medical School (UNZA-UCLMS) Research and Training Programme, University Teaching Hospital; Institute for Infectious Diseases, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
John
J
Tembo
Department of Pathology and Microbiology, University Teaching Hospital, Lusaka, Zambia.
Aaron
A
Shibemba
Norwich Medical School, University of East Anglia, Norwich, United Kingdom.
Justin
J
O'Grady
National TB and Leprosy Control Programme, Ministry of Community Development, Mother and Child Health, Lusaka, Zambia.
Nathan
N
Kapata
Department of Infection, Division of Infection and Immunity, University College London; National Institute for Health Research Biomedical Research Centre at UCL Hospitals, London, United Kingdom.
Alimuddin
A
Zumla
Department of Infection, Division of Infection and Immunity, University College London; National Institute for Health Research Biomedical Research Centre at UCL Hospitals, London, United Kingdom.
Matthew
M
Bates
D000904:Antibiotics, Antitubercular / Q000494:pharmacology*; D003937:Diagnosis, Differential; D024881:Drug Resistance, Bacterial / Q000235:genetics; D005260:Female; D005557:Formaldehyde; D015658:HIV Infections / Q000150:complications / Q000382:microbiology; D006652:Histological Techniques; D006801:Humans; D008198:Lymph Nodes / Q000382:microbiology; D008297:Male; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification*; D016612:Paraffin Embedding; D016133:Polymerase Chain Reaction; D012189:Retrospective Studies; D012293:Rifampin / Q000494:pharmacology*; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology; D016707:Tissue Fixation; D014059:Tongue / Q000382:microbiology; D014376:Tuberculosis / Q000150:complications / Q000175:diagnosis* / Q000382:microbiology; D014389:Tuberculosis, Male Genital / Q000175:diagnosis / Q000382:microbiology; D018088:Tuberculosis, Multidrug-Resistant / Q000175:diagnosis* / Q000382:microbiology; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis
D000904:Antibiotics, Antitubercular; D005557:Formaldehyde; D012293:Rifampin