Infectious disease guidelines recommend that antibiotics be administered to patients in whom bacterial meningitis is suspected within 30 minutes of their presentation.
Antibiotics do not appear to cause changes in cerebrospinal fluid (CSF) white blood cell, protein, or glucose levels which are compatible with impeding diagnostic utility.
Additionally, CSF gram stain findings are not significantly changed by early antibiotic use, as these studies have been found to be diagnostic in most patients even if lumbar puncture (LP) is delayed by up to 3 days.
CSF cultures may be positive even after a single dose of antibiotics, although the yield decreases with more fastidious organisms such as meningococcus.
In 86% of patients with bacterial meningitis, the causative organism may be isolated pre-antibiotic administration via blood culture.
TAKE HOME POINT: In cases of high suspicion for bacterial meningitis, do not delay administering antibiotics for the sake of first performing an LP, and have a low threshold to check blood cultures.
References
Hasburn, et al. Computed tomography of the head before lumbar puncture in adults with suspected meningitis. New England Journal of Medicine 2001; 345: 1727-33.
Mattu A, et al. Emergency Medicine: Avoiding the Pitfalls and improving the Outcomes. Pp 66-7. Copyright 2007.
Talan DA, et al. Relationship of clinical presentation to time to antibiotics for the emergency department management of suspected bacterial meningitis. Annals of Emergency Medicine 1993; 22:1733-8.
