Lumbar Puncture

Lumbar Puncture

Introduction: Antimicrobial therapy administered before lumber puncture (LP) in cases of suspected bacterial meningitis may affect the CSF culture yield, even if LP is performed within the proposed "minimum window" of 2 to 3 hours. The records of children with bacterial meningitis were reviewed retrospectively to determine the rate at which parenteral antibiotic pretreatment sterilizes CSF cultures.

Methods: Included in the review were patients discharged from the hospital over a 5 year period (1992 through 1996). Records were abstracted for demographic and historical data, microbiologica studies, chronologic data, and sequence of intervention. The time interval of interest was from the initiation of parenteral antibiotic therapy until the collection of the first pretreated CSF sample (or the first follow up CSF sample if serial LPs were performed). Patients were classified according to the time between initiation of parenteral antibiotic therapy and LP. The median patient age was 8 months.

Results: The most common pathogens that infected the 128 patients were Streptococcus pneumoniae (49), Neisseria meningitidis (37), and group B Streptococcus (21). Thirty nine children (30%) had first LPs after parenteral antibiotics were administered, and 55 (43%) had serial LPs both before and after the start of therapy. After at least 50 mg/kg of a third generation cephalosporin, 3 of 9 LPs in meningococcal meningitis were sterile within 1 hour and all were sterile by 2 hour. In cases of pneumococcal disease, the first negative CSF culture occurred at 4.3 hours; 5 of 7 cultures were negative from 4 to 10 hours after the start of parenteral antibiotic therapy. There was reduced susceptibility to B-lactam antibiotics in 11 of 46 pneumococcal isolates. Group B streptococcal cultures were positive through the first 8 hours after parenteral antibiotics were administered. Blood cultures were positive in 74% of the cases with no pretreatment and in 57% to 68% of the cases with negative CSF cultures.

Discussion: Sterilization of CSF cultures may occur sooner after the initiation of parenteral antibiotics than previously suggested, resulting in an inability to individualize therapy according to antimicrobial susceptibility. If feasible, patients with suspected meningitis should undergo LP before parenteral antibiotics are administered.