Diagnosis and Management of Bacterial Meningitis

Summary

Bacterial meningitis is one of the most important of medical emergencies and has its highest incidence in early childhood. It is responsible for a variable mortality and morbidity, despite the wide range of antibacterial drugs available. Early diagnosis is the most important factor in determining the final outcome, and delay may be associated with significant central nervous system handicap in survivors. It is especially important to entertain the diagnosis in very young children, in whom the accepted clinical signs of meningitis are frequently absent. After the first weeks of life, three organisms — Haemophilus influenzae, Neisseria meningitidis and Diplococcus pneumoniae — are responsible, in that order of frequency, for the majority of cases. In the neonatal period a wide variety of bacteria may cause meningitis, but Gram-negative organisms predominate.

Expert bacteriological advice is essential for proper interpretation of the Gram stain of cerebrospinal fluid. The newer technique of counter immunoelectrophoresis may also prove useful in rapid identification of the infecting organism. When immediate diagnosis is impossible, treatment should be started at once to cover the three most common pathogens, and ampicillin in a dose of 200 to 400 mg/kg/day intravenously, is at present acceptable. Dosage should not be decreased with clinical improvement, as cerebrospinal fluid penetration of the drug is directly related to the protein and cell content. Benzylpenicillin is the drug of choice for meningococcal and pneumococcal meningitis and can be substituted as the results of culture become known with certainty. If localising abnormal central nervous system signs are present when the patient is first seen, chloramphenicol may be preferred for H. influenzae meningitis, but in cases diagnosed early ampicillin remains, at present, the drug of choice. Drugs for intravenous use should not be mixed with acidic infusion fluids such as dextrose, but given as a slow injection at 4 or 6 hourly intervals. In the neonatal period, when the infecting organism is not known, a combination of ampicillin and gentamicin is advisable, and in meningitis due to Gram-negative organisms at least, and when hydrocephalus is present, intrathecal therapy will also be necessary.

There are still unanswered questions in the management of meningitis and new treatment regimens as other drugs become available need constant evaluation. Vigilant examination of the patient during the course of the illness is essential if complications are to be recognised and treated early. Follow up is important, and in very young children should always include an expert assessment of hearing. Prevention of meningitis may be a more positive line of approach for the future. The development of vaccines against H. influenzae and N. meningitidis is a step in this direction.