Background
Timely diagnosis of tuberculous meningitis (TBM) remains challenging. Molecular diagnostic tools are necessary, particularly in low- and middle-income countries. There is no approved commercial polymerase chain reaction (PCR) assay that can be used to detect Mycobacterium tuberculosis in non-respiratory samples, such as the cerebrospinal fluid (CSF). We aimed to validate the threshold cycle (Ct) cut-off points; calculate the operational characteristics of real-time PCR for detection of M. tuberculosis (MTb qPCR) in the CSF; and the inhibitory affect of CSF red blood cells (RBC) and total proteins on MTb qPCR.
Methods
A total of 334 consecutive participants were enrolled. Based on clinical, laboratory and imaging data, cases of suspected TBM were categorized as definite, probable, possible or not TBM cases. Receiver operating characteristic curve analysis was used to select the best discriminating Ct value.
Results
For TBM cases categorized as definite or probable (n=21), the Ct validated for CSF (≤39.5) improved the diagnostic performance of MTb qPCR on CSF samples. The sensitivity was 29%, specificity was 95%, positive predictive value was 26%, negative predictive value was 95%, efficiency was 90% and positive likelihood was 5.3. The CSF RBC and total protein did not affect the positivity of the MTb qPCR.
Conclusions
These data support the validation of a highly specific but low sensitive MTb qPCR assay for the TBM diagnosis using CSF samples. MTb qPCR contributes significantly to the diagnosis, mainly when associated with conventional microbiology tests and clinical algorithms.
Background:
Tuberculous meningitis (TbM) is the most severe complication of extrapulmonary tuberculosis (Tb).
There is higher frequency of positive cerebrospinal fluid (CSF) cultures for Mycobacterium tuberculosis (MTb) in samples from
human immunodeficiency virus (HIV) co-infected patients than in those from HIV-negative patients. We hypothesized that real
time PCR assays for MTb (MTb qPCR) using CSF would be more sensitive in HIV co-infected patients owing to a greater MTb
burden. The present study aimed to verify the diagnostic performance of MTb qPCR in CSF from TbM patients who either were
co-infected with HIV or were HIV-negative.
Methods:
We divided 334 consecutive participants with suspected TbM into two groups: HIV co-infected and HIV-negative; each
group was categorized into definite TbM, probable TbM, possible TbM, and TbM-negative subgroups based on clinical,
laboratory, and imaging data. We evaluated the diagnostic characteristics of MTb qPCR analysis to detect TbM in CSF by
comparing the results to those obtained for definite TbM (i.e., positive MTb culture) and/or probable TbM in CSF, as gold
standard.
Results:
The sensitivity of MTb qPCR in the definite and probable subgroups of the HIV co-infected participants (n = 14) was
35.7%, with specificity of 93.8%, negative predictive value (NPV) of 94.4%, and negative clinical utility index (CUI−) of 0.89.
Results of the HIV-negative group (n = 7) showed lower sensitivity (14.3%) and similar specificity, NPV, and CUI−.
Conclusion:
The findings confirmed our hypothesis, despite the low sensitivity. MTb qPCR may significantly contribute to
diagnosis when associated with clinical criteria and complementary examinations.
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