Bacterial meningitis can only be excluded in the presence of a negative cerebrospinal fluid culture if antibiotics were not previously used and there is an alternative explanation for coma. The initial choice of antibiotic therapy, prior to organism identification, varies greatly. Our choice is a combination of ampicillin (300 mg/kg per day divided in 2 doses in the first 7 days of life and 300 mg/kg per day divided in 3 doses thereafter) and gentamicin. In full term neonates, gentamicin is given at a dose of 2.5 mg/kg every 12 hours during the first 7 days of life and 2.5 mg/kg per dose every 8 hours thereafter. In premature neonates over 1000 grams, gentamicin is given at a dose of 2.5 mg/kg every 18 hours; in premature neonates weighing less than 1000 grams, gentamicin is given at a dose of 2.5 mg/kg every 24 hours. Gentamicin blood levels should be monitored. The final choice of antibiotics is determined from the results of CSF culture growth and sensitivity.
Herpes simplex encephalitis is usually caused by herpes simplex virus type 2 and occasionally type 1. The initial symptoms of encephalitis are irritability and seizure followed by coma. Encephalitis may present in an otherwise healthy-looking neonate or in a neonate with overt clinical evidence of systemic herpes simplex infection. Conjunctivitis and a vesicular eruption on the scalp or buttocks may be present. Giemsa staining of the scraping from the base of the vesicles reveals multinucleated giant cells with intranuclear inclusion (Figure 68.1). Viral antigens may also be detected from the vesicles smear by immunofluorescence. A periodic pattern of slow-wave or spike discharges is often seen on EEG. Cerebrospinal fluid usually shows polynuclear or mononuclear pleocytosis, increased protein, and an increased number of red cells if hemorrhagic necrosis of the brain parenchyma has occurred. In 15 neonates with culture positive herpes type 2 encephalitis, CSF white blood cell count ranged from 9 to 545 (mean: 113); protein concentration ranged from 82 to 396 mg/dL (mean: 103.7).

Figure 68.1.— Giemsa stain showing multinucleated giant cells.