Evaluation of the molecular assays for detection of Mycobacterium tuberculosis complex in extrapulmonary specimens

Abstract

Introduction: Tuberculosis, one of the most common and deadly infectious diseases, mainly affects the lungs, but can involve all tissues and organs. Diagnosis of extrapulmonary tuberculosis may be more challenging than pulmonary tuberculosis, which may lead to delay in starting treatment. In our study, it was aimed to determine the diagnostic value of FluoroType MTB, GeneXpert MTB/RIF, GeneXpert MTB/RIF Ultra molecular tests in extrapulmonary specimens. Materials and Methods: Extrapulmonary clinical materials were subjected to Kinyoun staining for acid fast bacilli and cultivation was done on Lowenstein Jensen media and BACTEC MGIT 960 automated culture system (BD). Results were compared with FluoroType MTB and GeneXpert MTB/RIF test results (2018) and with FluoroType MTB and GeneXpert MTB/RIF Ultra tests results (2019). Results: A total number of 892 extrapulmonary specimens were enrolled in the study. In 2018, positivity was detected in 16 (3.4%) of 467 specimens by molecular methods. Compared with culture; the sensitivity and specifity of the FluoroType MTB were 76.92%, 98.88% respectively; the sensitivity and specifity of GeneXpert MTB/RIF were 100%, 98.96% respectively. In 2019, positivity was detected in 15 (3.5%) of 425 specimens by molecular methods. The sensitivity and specifity of the FluoroType MTB was 62.5%, 98.05% respectively; the sensitivity and specificity of GeneXpert MTB/RIF Ultra was 100%, 99.36% respectively. Conclusion: Although culture is the gold standard method in the diagnosis of tuberculosis, the patients were diagnosed only with polymerase chain reaction positivity, supported by the patient’s clinical, radiology and pathology results in seven cases. The diagnosis of tuberculosis in extrapulmonary specimens is more challenging than in pulmonary specimens due to low bacillary burden and requiring invasive procedures for sampling. It should be considered that molecular methods have a critical role in diagnosis.