Analysis of bacterial isolates from cerebrospinal fluid.

We set out to determine the frequency of occurrence of contamination of cerebrospinal fluid with bacteria, seeking also to identify aids to differentiating contaminants from etiologically significant isolates. From 2,091 specimens, 182 bacterial isolates were obtained from 129 patients. Meningitis was the source of 81 isolates (32 patients); contamination yielded 101 isolates (97 patients). The cell counts and protein and glucose concentrations in the cerebrospinal fluid were significantly more often abnormal in specimens from patients with meningitis. Haemophilus influenzae and enteric gram-negative bacilli were usually cause for meningitis, whereas Staphylococcus epidermidis was the most common contaminant. In view of the reported high rate of procedural error in carrying out lumbar puncture, a program aimed at teaching proper technique is recommended to decrease the frequency of false-positive cultures of cerebrospinal fluid.