pediatrics
Neonatal Bacterial Meningitis
Diagnosis of Neonatal Bacterial Meningitis
Cerebrospinal fluid (CSF) cell counts, glucose and protein levels, Gram stain, and culture Polymerase chain reaction (PCR) testing Sometimes ultrasonography or CT or MRI of the brain Definitive diagnosis of neonatal bacterial meningitis is made by CSF examination via lumbar puncture (LP), which should be done in any neonate suspected of having sepsis or meningitis. However, LP can be difficult to do in a neonate, and there is some risk of the procedure causing hypoxia. Poor clinical condition (eg, respiratory distress, shock, thrombocytopenia) makes LP risky. If LP is delayed, the neonate should be treated as though meningitis is present. Even when the clinical condition improves, the presence of inflammatory cells and abnormal glucose and protein levels in CSF days after illness onset can still suggest the diagnosis. A needle with a trocar should be used for LP to avoid introducing epithelial rests and subsequent development of epitheliomas. The CSF, even if bloody or acellular, should be cultured. About 15 to 35% of neonates with negative blood cultures have positive CSF cultures depending on the population studied. If CSF cultures are negative, multiplex PCR panels to test CSF for multiple common pathogens can be done if bacterial meningitis is suspected (eg, if culture may have been affected by prior antibiotic use). LP should be repeated at 24 to 48 hours if clinical response is questionable and at 72 hours when gram-negative organisms are involved (to ensure sterilization). Repeating the CSF analysis helps guide duration of therapy and predict prognosis. Some experts believe that a repeat LP at 24 to 48 hours in neonates with GBS meningitis has prognostic value. LP should not be repeated at the end of therapy if the neonate is doing well. Normal CSF values are controversial and in part age-related. In general, both term and preterm infants without meningitis have≤20 white blood cells/mcL (0.02 × 109/L), one fifth of which may be polymorphonuclear leukocytes, in their CSF. CSF protein levels in the absence of meningitis are more variable; term infants have levels of<100 mg/dL (1 g/L), whereas preterm infants have levels up to 150 mg/dL (1.5 g/L). CSF glucose levels in the absence of meningitis are>75% of the serum value measured at the same time. These levels may be as low as 20 to 30 mg/dL (1.1 to 1.7 mmol/L). Bacterial meningitis has been identified by culture in neonates with normal CSF indices, showing that normal CSF values do not exclude a diagnosis of meningitis. Ventriculitis is suspected in a neonate not responding appropriately to antimicrobial therapy. The diagnosis is made when a ventricular puncture yields a white blood cell count greater than that from the LP, by a positive Gram stain or culture of ventricular fluid, or by increased ventricular pressure. When ventriculitis or brain abscess is suspected, ultrasonography or MRI or CT with contrast may aid diagnosis; dilated ventricles also confirm ventriculitis. 