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Efficient diagnosis of tuberculous meningitis by detection of Mycobacterium tuberculosis DNA in cerebrospinal fluid filtrates using PCR

¹ Department of Biotechnology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110029, India

² Department of Biochemistry and Department of Pediatrics, Dr Ram Manohar Lohia Hospital, New Delhi 110001, India

Correspondence
Jaya Sivaswami Tyagi
jstyagi{at}aiims.ac.in

Received August 20, 2008
Accepted January 19, 2009

Tuberculous meningitis (TBM) is the most devastating form of meningitis and prompt diagnosis holds the key to its management. Conventional microbiology has limited utility and nucleic acid-based methods have not been widely accepted for various reasons. In view of the paucibacillary nature of cerebrospinal fluid (CSF) and the recent demonstration of free Mycobacterium tuberculosis DNA in clinical specimens, the present study was designed to evaluate the utility of CSF ‘filtrates’ for the diagnosis of TBM using PCR. One hundred and sixty-seven CSF samples were analysed from patients with ‘suspected’ TBM (n=81) and a control group including other cases of meningitis or neurological disorders (n=86). CSF ‘sediments’ and ‘filtrates’ were analysed individually for M. tuberculosis DNA by quantitative real-time PCR (qRT-PCR) and conventional PCR. Receiver-operating characteristic curves were generated from qRT-PCR data and cut-off values of 84 and 30 were selected for calling a ‘filtrate’ or ‘sediment’ sample positive, respectively. Based on these, TBM was diagnosed with 87.6 % and 53.1 % sensitivity (P <0.001) in ‘filtrates’ and ‘sediments’, respectively, and with 92 % specificity each. Conventional devR and IS6110 PCR were also significantly more sensitive in ‘filtrates’ versus ‘sediments’ (sensitivity of 87.6 % and 85.2 % vs 31 % and 39.5 %, respectively; P <0.001). The qRT-PCR test yielded a positive likelihood ratio of 11 and 6.6 by analysing ‘filtrate’ and ‘sediment’ fractions, respectively, which establishes the superiority of the ‘filtrate’-based assay over the ‘sediment’ assay. PCR findings were separately verified in 10 confirmed cases of TBM, where M. tuberculosis DNA was detected using devR PCR assays in ‘sediment’ and ‘filtrate’ fractions of all samples. From this study, we conclude that (i) CSF ‘filtrates’ contain a substantial amount of M. tuberculosis DNA and (ii) ‘filtrates’ and not ‘sediments’ are likely to reliably provide a PCR-based diagnosis in ‘suspected’ TBM patients.

Abbreviations: CIIMS, Central India Institute of Medical Sciences; CNS, central nervous system; CSF, cerebrospinal fluid; NIND, non-infectious neurological disorders; NTIM, non-tuberculous infectious meningitis; OIND, other infectious neurological disorders; qRT-PCR, quantitative real-time PCR; RML, Dr Ram Manohar Lohia Hospital; ROC, receiver-operating characteristic; TB, tuberculosis; TBM, tuberculous meningitis; USP, universal sample processing.

Supplementary tables are available with the online version of this paper.