Listeria monocytogenes meningitis in previously healthy adults.

A retrospective study of four sporadic cases of Listeria monocytogenes meningitis is reported. Contrary to the conventional epidemiology these patients were adults who were not immuno-compromised. Although all four cases produced positive cerebrospinal fluid cultures, in three, listeria was not microscopically identified. Protein and glucose contents of cerebrospinal fluids were variable and all samples showed lymphocytic pleocytosis. All four had neutrophil leucocytosis in peripheral blood. The unwary may dismiss lymphocytic meningitis as being of 'viral' origin, thereby making an important diagnostic misjudgement of vital therapeutic importance. Intravenous ampicillin is the drug of first choice for treatment of listeria meningitis; third generation cephalosporins are ineffective.