Interpretation of Lumbar Puncture Cultures After Parenteral Antibiotic Pretreatment
Abstract & Commentary
Synopsis: Sterilization of CSF after an initial dose of parenteral antibiotic therapy occurred within 2 hours for Neisseria meningitidis, began at 4 hours for Streptococcus pneumoniae, and after 8 hours for group B Streptococcus.
Source: Kanegaye JT, et al. Lumbar puncture in pediatric bacterial meningitis: Defining the time interval for recovery of cerebrospinal fluid pathogens after parenteral antibiotic pretreatment. Pediatrics. 2001;108:1169-1174.
A retrospective analysis of 128 pediatric patients with bacterial meningitis was performed to define the rate at which parenteral antibiotic therapy sterilizes the cerebrospinal fluid (CSF). Causative organisms included Streptococcus pneumoniae (49), Neisseria meningitidis (37), group B Streptococcus (21), Haemophilus influenzae (8, including 5 type b, 1 type e, 1 type f, and 1 not typed), Escherichia coli (4), other organisms (7), and undetermined (3); 1 patient had both S pneumoniae and H influenzae isolated. Of the 128 patients, 39 (30%) had an initial lumbar puncture after the first dose of parenteral antibiotics, and 55 (43%) had serial lumbar punctures before and after initiation of antibiotics. For meningococcal meningitis, 3 of 9 CSF cultures were sterile within 1 hour, after a dose of 150 mg/kg of a third-generation cephalosporin, some as early as 15 minutes, with all cultures sterile by 2 hours. For pneumococcal meningitis, the first sterile culture was documented at 4.3 hours, with 5 of 7 cultures obtained from 4-10 hours being sterile. The 46 pneumococcal isolates (3 patients with pneumococcal meningitis had no positive cultures) included 11 (24% of isolates) with MIC to penicillin of > 0.1 mg/mL and 4 (9%) with MIC to ceftriaxone/cefotaxime of > 1.0 mg/mL. For group B streptococcal meningitis, CSF cultures remained positive through the first 8 hours of parenteral antibiotics. For all cases, negative-CSF cultures occurred in 44% of initial lumbar punctures after parenteral antibiotics, compared to only 8% before parenteral antibiotics and 3% with neither oral nor parenteral antibiotics. Blood cultures were positive in 74% of cases without pretreatment and 57-68% of cases with negative-CSF cultures.
Comment by Hal B. Jenson, MD, FAAP
This study shows that sterilization of the CSF with meningococcal meningitis occurs as early as 15 minutes after initiating parenteral antibiotic therapy, with uniform sterilization by 2 hours. In contrast, sterilization with pneumococcal meningitis usually occurs after 4 hours of therapy. Sterilization with group B streptococcal meningitis is apparently achieved more slowly, in this report between 8 and 33.5 hours after initiating parenteral therapy.
A lumbar puncture for analysis of CSF remains the optimum test for the diagnosis of bacterial meningitis and should be performed as soon as possible. The benefits of early diagnosis outweigh the minimal risks of herniation associated with mild-to-moderate increased intracranial pressure, which is relatively common in bacterial meningitis. The risk of herniation is further diminished in young infants if the fontanelles are open. If severe increased intracranial pressure is suspected because of papilledema, dilated nonreactive pupils, abnormal ocular mobility suggesting sixth nerve palsy, bradycardia, hypertension or stupor, the lumbar puncture should be postponed until CT scan is performed.
There are very few contraindications besides severe increased intracranial pressure to lumbar puncture in the evaluation of bacterial meningitis. In some instances, such as hemodynamic instability or inability to successfully perform a lumbar puncture, both of which are more likely in neonates and young infants, it may be necessary to initiate parenteral antibiotic treatment prior to obtaining CSF. Under such circumstances, this study confirms that the accuracy of the CSF culture is adversely affected, which may diminish the ability of the clinician to accurately diagnosis bacterial meningitis. The rapidity of CSF sterilization following parenteral antibiotic treatment greatly negates the reliability of CSF culture with delayed lumbar puncture, which may necessitate treatment for the possibility of bacterial meningitis if other studies such as antigen studies and CSF cell counts are insufficient to exclude the diagnosis.
Dr. Jenson, Chief, Pediatric Infectious Diseases, University of Texas Health Science Center, San Antonio, TX, is Associate Editor of Infectious Disease Alert.
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