Despite the lack of evidence defining a time interval during which cerebrospinal fluid (CSF) culture yield will not be affected by previous antibiotic therapy, recent publications cite a “minimum window” of 2 to 3 hours for recovery of bacterial pathogens after parenteral antibiotic administration. We conducted a retrospective review of children with bacterial meningitis to describe the rate at which parenteral antibiotic pretreatment sterilizes CSF cultures.
The medical records of pediatric patients who were discharged from a tertiary children's hospital during a 5-year period with the final diagnosis of bacterial meningitis or suspected bacterial meningitis were reviewed. The decay in yield of CSF cultures over time was evaluated in patients with lumbar punctures (LP) delayed until after initiation of parenteral antibiotics and in patients with serial LPs before and after initiation of parenteral antibiotics.
The pathogens that infected the 128 study patients were Streptococcus pneumoniae (49),Neisseria meningitidis (37), group BStreptococcus (21), Haemophilus influenzae (8), other organisms (11), and undetermined (3). Thirty-nine patients (30%) had first LPs after initiation of parenteral antibiotics, and 55 (43%) had serial LPs before and after initiation of parenteral antibiotics. After ≥50 mg/kg of a third-generation cephalosporin, 3 of 9 LPs in meningococcal meningitis were sterile within 1 hour, occurring as early as 15 minutes, and all were sterile by 2 hours. With pneumococcal disease, the first negative CSF culture occurred at 4.3 hours, with 5 of 7 cultures negative from 4 to 10 hours after initiation of parenteral antibiotics. Reduced susceptibility to β-lactam antibiotics occurred in 11 of 46 pneumococcal isolates. Group B streptococcal cultures were positive through the first 8 hours after parenteral antibiotics. Blood cultures were positive in 74% of cases without pretreatment and in 57% to 68% of cases with negative CSF cultures.
The temptation to initiate antimicrobial therapy may override the principle of obtaining adequate pretreatment culture material. The present study demonstrates that CSF sterilization may occur more rapidly after initiation of parenteral antibiotics than previously suggested, with complete sterilization of meningococcus within 2 hours and the beginning of sterilization of pneumococcus by 4 hours into therapy. Lack of adequate culture material may result in inability to tailor therapy to antimicrobial susceptibility or in unnecessarily prolonged treatment if the clinical presentation and laboratory data cannot exclude the possibility of bacterial meningitis.