In neonates, the most common causes of meningitis in the United States are group B Streptococcus, E. coli, and L. monocytogenes. Other organisms that cause meningitis include S. pneumoniae, other streptococci, nontypeable H. influenzae, Staphylococcus species, Klebsiella, Enterobacter, Pseudomonas, Treponema pallidum, and M. tuberculosis.9 Neonates can develop meningitis from primary viral infection with HSV or enteroviruses. The differential diagnosis of neonatal sepsis and meningitis includes infection from fungi (Candida) and protozoa (malaria crosses the placenta, and maternal malaria can infect the neonate). Noninfectious illnesses that can appear similar to sepsis and meningitis include cardiac disease, necrotizing enterocolitis, congenital adrenal hyperplasia, inborn errors of metabolism, and intracranial hemorrhage.
In older infants and children, the usual dilemma is differentiating acute viral and bacterial meningitis. The typical bacterial causes are N. meningitides, S. pneumoniae, and H. influenzae type b. Less common organisms include M. tuberculosis, Nocardia species, T. pallidum, and B. burgdorferi.2 Fungal infections and parasitic infections can produce infection of the CNS. Infections around the brain and spinal cord may appear similar to meningitis. Collagen vascular disease, malignancy, and certain drugs and toxins should also be included in the differential diagnosis.
All children suspected of having meningitis should undergo a lumbar puncture when they are clinically stable. Although establishing a diagnosis is important, patients who are unstable but suspected of having bacterial meningitis should receive antibiotics as quickly as possible (see Table 114B-1). Defer lumbar puncture until the child is stabilized and can tolerate the procedure. Positioning an infant or child for lumbar puncture before stabilization can result in hypoxia and hypotension. There are a few contraindications to lumbar puncture in children besides hypoxia and clinical instability. These include focal neurologic findings, thrombocytopenia, local infection at the lumbar site, and vertebral abnormalities. See Chapter 114A, Fever and Serious Bacterial Illness, for details of pediatric lumbar puncture.
Table 114B-1 ED Treatment of Bacterial Meningitis by Age Group |Favorite Table|Download (.pdf)
Table 114B-1 ED Treatment of Bacterial Meningitis by Age Group
Neonatal Meningitis Treatment
Meningitis Treatment in Older Infants and Children
Ampicillin* 50 milligrams/kg every 6 h
Cefotaxime† 75 milligrams/kg every 6 h
Ceftriaxone† 100 milligrams/kg every 24 h
Gentamicin 2.5 milligrams/kg every
12 h for 0–7 days old; every 8 h for >7 days old
Cefotaxime* 100 milligrams/kg every 8 h
AND if herpes suspected
AND if herpes suspected
Acyclovir 20 milligrams/kg every 8 h
Acyclovir 20 milligrams/kg every 8 h
Children with focal neurologic signs should undergo a head CT scan prior to lumbar puncture and should receive antibiotics promptly without waiting for the results of the scan or lumbar puncture. CSF abnormalities of meningitis, such as neutrophilic pleocytosis, low glucose, and high protein, will persist for days despite antibiotic treatment. Bacteria are generally not evident on Gram stain after antibiotics have penetrated the CSF (time intervals for clearance of bacteria in the CSF range from 15 minutes to several hours; see later section, "The Child Pretreated with Antibiotics").
Spinal fluid should be sent for cell count, protein, glucose, Gram stain, and culture. In the event of a traumatic tap, send fluid for culture and use clinical judgment in the interpretation of other results. Decision rules correcting the WBC count based on the number of red cells may not be reliable.
The CSF of patients with bacterial meningitis tends to have lower glucose, higher protein, higher WBC counts, and a more frequent predominance of neutrophils relative to the CSF of patients with viral meningitis, but there is considerable overlap between the two groups.12-14 Data for the development of the Bacterial Meningitis Score were collected on children from 20 U.S. EDs from 2001 to 2004, and any one of the following risk factors was associated with bacterial meningitis: CSF protein >80 micrograms/L; positive CSF Gram stain; peripheral absolute neutrophil count ≥10,000 cells/μL; CSF absolute neutrophil count ≥1000 cells/μL; or a seizure before or after presentation.15 The Bacterial Meningitis Score predicted a very low risk of bacterial meningitis for those children with none of the above risk factors (sensitivity, 98.3%; negative predictive value, 99.9%). Two children, both <2 months old, had bacterial meningitis despite a negative Bacterial Meningitis Score. The overall worldwide generalizability of the score, or its stability in view of a country's vaccination practices, is not known. The biomarkers of erythrocyte sedimentation rate, C-reactive protein, interleukin-6, and procalcitonin do not perform robustly enough to serve as proxies for lumbar puncture and examination and culture of CSF.
Polymerase chain reaction is especially helpful in diagnosing viral meningitis. Polymerase chain reaction is available for HSV, Epstein-Barr virus, enterovirus, and cytomegalovirus, as well as others. Polymerase chain reaction is useful for the diagnosis of meningitis due to tuberculosis and is sensitive for acute neurosyphilis as well.16
Latex agglutination testing has been proposed for the rapid diagnosis of bacterial meningitis, particularly when the patient has already received antibiotics. However, testing is only available for certain bacteria. Furthermore, sensitivity varies depending on the organism. A negative test does not rule out bacterial meningitis. Although latex agglutination testing may be helpful in certain situations, it is not recommended for routine use.17,18 Counterimmunoelectrophoresis can also be used for identifying bacterial causes of meningitis. It requires special equipment and is cumbersome to perform.19 Counterimmunoelectrophoresis has relatively poor specificity, creating a number of false positives.