ORIGINAL ARTICLE

Improved case confirmation in meningococcal disease with whole blood Taqman PCR

S J Hackett¹, E D Carrol¹, M Guiver², J Marsh², J A Sills¹, A P J Thomson¹, E B Kaczmarski², C A Hart³

¹ Institute of Child Health, Royal Liverpool Childrens NHS Trust-Alder Hey, Eaton Road, Liverpool L12 2AP, UK
² PHLS Meningococcal Reference Unit (MRU), Withington Hospital, Manchester M20 2LR, UK
³ Department of Medical Microbiology, Duncan Building, Liverpool University, Daulby Street, Liverpool L69 3GA, UK

Correspondence to:
Correspondence to:
Dr S Hackett, Department of Medical Microbiology, Duncan Building, Liverpool University, Daulby Street, Liverpool L69 3GA, UK;
scott.hackett{at}liv.ac.uk

Background: The clinical diagnosis of meningococcal disease (MCD) can be difficult. Non-culture methods like the previous ELISA meningococcal PCR improved case confirmation rates, but were not ideal. A Taqman meningococcal PCR, using DNA extracted from serum (S-Taqman), which has an improved sensitivity compared to the ELISA method in vitro, was introduced into clinical practice in July 1997. A new whole blood DNA extraction method for Taqman (WB-Taqman) was introduced in September 1999.

Aims: To determine the degree of improvement in the confirmation rate in clinically diagnosed MCD, following the introduction of WB-Taqman.

Methods: A total of 192 patients (WB-Taqman) with possible or probable MCD, including those admitted to our paediatric intensive care unit, were studied. Admission EDTA samples obtained were sent for bacterial DNA detection at the Meningococcal Reference Unit (MRU), Manchester. These patients were compared to 319 patients with possible and probable MCD, seen at the same hospital prior to the introduction of WB-Taqman.

Results: Following the introduction of WB-Taqman, 82 of the 95 probable cases (88%) had a positive meningococcal PCR result. This gives a diagnostic sensitivity and specificity for WB-Taqman of 87% and 100% respectively. Following WB-Taqman all blood culture positive patients were also PCR positive. Confirmation of cases by PCR rose from 47% (S-Taqman, n = 166) to 88% (WB-Taqman). When all confirmatory tests were included, case confirmation increased from 72% (S-Taqman) to 94% (WB-Taqman).

Conclusion: The sensitivity of PCR in confirming clinical MCD has improved significantly with this new method. The gold standard for confirming cases of MCD is now the WB-Taqman PCR.

Keywords: meningococcal disease; Taqman PCR; case confirmation, Neisseria meningitidis

Abbreviations: CRP, C reactive protein; CSF, cerebrospinal fluid; LP, lumbar puncture; MCD, meningococcal disease; MRU, Meningococcal Reference Unit; PCR, polymerase chain reaction; RLA, rapid latex antigen

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