UMHS LOGOUniversity of Michigan
Department of Pediatrics

Evidence-Based Pediatrics Web Site

PMN Predominance of CSF in Meningitis is Poorly Predictive of Bacterial vs. Aseptic Etiology


  • In patients aged 3 months to 18 years presenting with meningitis (defined as CSF pleiocytosis > 20x106 WBC/mm3) during the months of April-October (peak enterovirus season), is a polymorphonuclear (PMN) predominance predictive of bacterial versus aseptic etiology as determined by CSF/blood culture results.

Clinical Bottom Lines

  1.  During peak season for viral meningitis (April to October in this study), the percent of PMNs is poorly predictive of bacterial meningitis. In fact, it is more often associated with aseptic meningitis, due to the significantly higher incidence of this disease during this time period. (PPV/+LR for bacterial disease = 19%/1.6)
  2.  The cell differential did not vary with the time from onset of symptoms -- a PMN predominance was as likely to be seen late in aseptic meningitis (> 48 hours) as it was earlier in the course of disease.
  3.  A CSF differential containing <50% PMNs may be helpful in excluding the diagnosis of bacterial meningitis during this season. (NPV = 97%; -LR = 0.23).

Summary of Key Evidence

Target disorder (Bacterial Meningitis)
Diagnostic test result (%PMNs)
Positive (>50%)
18 (a)
78 (b)
96 (a+b)
Negative (<50%)
2 (c)
60 (d)
62 (c+d)
20 (a+c)
138 (b+d)
  1.   No association was found between the percentage PMNs and time from onset of symptoms to LP.

Additional Comments

  •  Excluded were children with recent (within 5 days) antibiotic exposure, immunodeficiency or neurosurgical procedures/prostheses.
  •  Other authors2,3 have reported similar findings.


  1. Negrini B, Kelleher KJ, Wald ER. Cerebrospinal fluid findings in aseptic versus bacterial meningitis. Pediatrics 2000; 105: 316-319.
  2. Spanos A, Harrell FE, Durack DT. Differential diagnosis of acute meningitis. JAMA 1989; 262:2700-2707.
  3. Freedman et al. Predictors of meningitis in the post-Haemophilus Influenza era. Archives of Pediatrics and Adolescent Medicine 2001; in press.

CAT Author: Cameron Dezfulian, MD

CAT Appraisers: Katherine Layton , MD

Date appraised: October 8, 2001

Last updated October 24, 2001
Department of Pediatrics and Communicable Diseases
© 1998-2002 University of Michigan Health System