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Bacterial Meningitis
The presence of bacterial meningitis is suspected on clinical grounds. Bacterial meningitis is tentatively diagnosed by an abnormal cerebrospinal fluid cell count, sugar level, and protein concentration, and the detection of antigen in the cerebrospinal fluid. Bacterial meningitis is conclusively diagnosed by cerebrospinal fluid Gram-stained smear and culture. Meningitis usually occurs with late-onset (after 7 days) sepsis. Seizures may be the first sign of meningitis. Neonates with bacterial meningitis are usually lethargic after the seizures. The anterior fontanel may be bulging. Neck rigidity may be present. Seizures in neonates with meningitis are usually due to microscopic or macroscopic ischemic vascular parenchymal lesions but the possibility of hypocalcemia, hypoglycemia, hyponatremia, abscess, and subdural empyema should be considered. The organisms usually associated with bacterial meningitis are group B streptococcus, Escherichia coli, Listeria monocytogenes, Staphylococcus aureus, and Pseudomonas aeruginosa.
The tentative diagnosis of bacterial meningitis should be made in neonates with seizures if the cerebrospinal fluid shows less than 100 red blood cells per cubic millimeter and more than 11 white blood cells per cubic millimeter (90% of neonates without meningitis have 11 white blood cells per cubic millimeter or less) or if organisms are present in the Gram-stained smear. Neonates with seizures having any of these parameters should be treated with antibiotics while awaiting the results of the CSF culture. These patients should undergo a careful physical examination searching for a primary source of infection such as otitis media, arthritis, or skin infection.
For practical purposes, a negative cerebrospinal fluid culture eliminates the possibility of bacterial meningitis if the Gram-stained smear is also negative and the patient did not receive antibiotics before the lumbar puncture. If a cerebrospinal fluid culture is negative but the Gram-stained smear is positive, or the patient received antibiotic treatment before the lumbar puncture was done, a full course of antibiotics should be administered.
An MRI of the brain should be performed when the patient is stable or if deterioration occurs after initiation of treatment or fever persists after several days of the appropriate antibiotic treatment. Deterioration raises the possibility of localized intracranial infection. Localized intracranial infections include brain abcesses, subdural empyema, and ventriculitis.
The choice of antibiotics depends on the type of organism isolated and its sensitivity. Prior to isolation of the organism, treatment should be initiated with ampicillin and gentamicin.

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Davis, 1994 Ahmed, 1996 Davis, 1994