The Diagnostic Utility of Bact/ALERT and Nested PCR in the Diagnosis of Tuberculous Meningitis

A Systematic Review and Meta-analysis of the Diagnostic Accuracy of Nucleic Acid Amplification Tests for Tuberculous Meningitis

The diagnosis of tuberculous meningitis (TBM) is difficult and poses a significant challenge to physicians worldwide. Recently, nucleic acid amplification (NAA) tests have shown promise for the diagnosis of TBM, although their performance has been variable. We undertook a systematic review and meta-analysis to evaluate the diagnostic accuracy of NAA tests with cerebrospinal fluid (CSF) samples against that of culture as the reference standard or a combined reference standard (CRS) for TBM. We searched the Embase, PubMed, Web of Science, and Cochrane Library databases for the relevant records. The QUADAS-2 tool was used to assess the quality of the studies. Diagnostic accuracy measures (i.e., sensitivity and specificity) were pooled with a random-effects model. All statistical analyses were performed with STATA (version 14 IC; Stata Corporation, College Station, TX, USA), Meta-DiSc (version 1.4 for Windows; Cochrane Colloquium, Barcelona, Spain), and RevMan (version 5.3; The Nordic Cochrane Centre, the Cochrane Collaboration, Copenhagen, Denmark) software. Sixty-three studies comprising 1,381 cases of confirmed TBM and 5,712 non-TBM controls were included in the final analysis. These 63 studies were divided into two groups comprising 71 data sets (43 in-house tests and 28 commercial tests) that used culture as the reference standard and 24 data sets (21 in-house tests and 3 commercial tests) that used a CRS. Studies which used a culture reference standard had better pooled summary estimates than studies which used CRS. The overall pooled estimates of sensitivity, specificity, positive likelihood ratio (PLR), and negative likelihood ratio (NLR) of the NAA tests against culture were 82% (95% confidence interval [CI], 75 to 87%), 99% (95% CI, 98 to 99%), 58.6 (95% CI, 35.3 to 97.3), and 0.19 (95% CI, 0.14 to 0.25), respectively. The pooled sensitivity, specificity, PLR, and NLR of NAA tests against CRS were 68% (95% CI, 41 to 87%), 98% (95% CI, 95 to 99%), 36.5 (95% CI, 15.6 to 85.3), and 0.32 (95% CI, 0.15 to 0.70), respectively. The analysis has demonstrated that the diagnostic accuracy of NAA tests is currently insufficient for them to replace culture as a lone diagnostic test. NAA tests may be used in combination with culture due to the advantage of time to result and in scenarios where culture tests are not feasible. Further work to improve NAA tests would benefit from the availability of standardized reference standards and improvements to the methodology.

Identification of Mycobacterium tuberculosis in Clinical Specimens of Patients Suspected of Having Extrapulmonary Tuberculosis by Application of Nested PCR on Five Different Genes

Definitive and rapid diagnosis of extrapulmonary tuberculosis (EPTB) is challenging since conventional techniques have limitations due to the paucibacillary nature of the disease. To increase the sensitivity of detection of Mycobacterium tuberculosis (MTB) in EPTB specimens, we performed a nested PCR assay targeting several genes of MTB on EPTB specimens. A total of 100 clinical specimens from suspected cases of EPTB were processed. Standard staining for acid fast bacilli (AFB) was performed as the preliminary screening test. Extracted DNAs from specimens were subjected to Nested PCR technique for the detection of five different MTB target genes of IS6110, IS1081, hsp65kd, mbp64, and mtp40. On performing AFB staining, only 13% of specimens were positive, of which ascites fluid (33.3%), followed by pleural effusion (30.8%) showed the greatest AFB positivity rate. We demonstrated slight improvement in yields in lymph node which comprised the majority of specimens in this study, by employing PCR targeted to IS6110- and hsp65-genes in comparison to AFB staining. However, the yields in ascites fluid and pleural effusion were not substantially improved by PCR, but those from bone and wound were, as in nested PCR employing either gene, the same positivity rate were obtained for ascites fluid (33.3%), while for pleural effusion specimens only IS1081 based PCR showed identical positivity rate with AFB stain (30.8%). The results for bone and wound specimens, however, demonstrated an improved yield mainly by employing IS1081 gene. Here, we report higher detection rate of EPTB in clinical specimens using five different targeted MTB genes. This nested PCR approach facilitates the comparison and the selection of the most frequently detected genes. Of course this study demonstrated the priority of IS1081 followed by mtp40 and IS6110, among the five tested genes and indicates the effectiveness of any of the three genes in the design of an efficient nested-PCR test that facilitates an early diagnosis of paucibacillary EPTB cases, which are difficult to diagnose with the available standard.