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Editor,—The numbers of cases of meningococcal disease diagnosed clinically and by polymerase chain reaction (PCR) have increased, while the numbers of culture confirmed cases and lumbar punctures are falling.1 ,2 This changing trend in case ascertainment was noted by Gill.3 Pollardet al seem to support this trend,4 preferring to avoid lumbar puncture in all patients with “clinically obvious” meningococcal disease because it “adds little useful information to the clinical diagnosis, it could be misleading, and does not affect clinical treatment”. I find this surprising for several reasons.
Firstly, it is at odds with their view on treatment, that a broad spectrum third generation cephalosporin should be used “until microbiological information is available” and possible penicillin resistance or alternative bacterial causes of purpura are excluded. Cerebrospinal fluid (CSF) may provide this information, and could thus contribute significantly to diagnosis and management. Also, identifying a bacterium other than meningococcus or Haemophilus influenzae would avert unnecessary antibiotic prophylaxis of contacts.
Secondly, CSF microscopy could confirm the diagnosis of meningococcal disease within the hour. Blood and throat cultures take at least 12 hours; and although PCR itself only takes 2 hours,2 in practice the need to transport the sample to the Meningococcal Reference Unit in Manchester—particularly over the weekend—may delay results for several days. It must benefit clinicians and the patient's family to have the diagnosis confirmed quickly.
Thirdly, isolating the causative meningococcus does not just make the microbiologist happy, it can also provide valuable clinical and epidemiological information. PCR of blood can identify the capsular serogroup, but the actual organism is required to determine antibiotic sensitivities and other phenotypic characteristics. Compared to blood (54% (88/164)) and throat (31% (22/71)) cultures, CSF (70% (96/138)) offers the highest chance of isolating meningococci, particularly when pre-admission antibiotics are given.1
Finally, an initially normal CSF is well recognised in meningitis cases and should be no more misleading than an initially normal white blood count or C reactive protein. Therefore, in the absence of contraindications, there are still good reasons to proceed with lumbar puncture in patients with purpura characteristic of meningococcal disease.