Acute meningitis of unknown aetiology: analysis of 219 cases admitted to hospital between 1977 and 1990.

Clinical and biochemical parameters in 219 patients with meningitis of unknown aetiology were analyzed according to their initial CSF leucocyte count. The male/female ratio was 1.1 and the median age 30 years,(males = 22 years/females = 42 years). Pre-admission antibiotic, which may inhibit bacterial growth, was given to 28% patients. On admission symptoms of meningitis were predominant: 96% had fever, 91% neck rigidity and 19% a severely affected mental state. In addition, 10% had a petechial rash. A bacterial aetiology was likely, as 91% had a predominance of polymorphonuclear leucocytes in the CSF and in 50% it was frankly purulent. The CSF leucocyte count correlated positively with age, the period of fever and the length of hospitalization, but did not relate to the 10.1% in-patient mortality rate. Mortality was related to advancing age, but not to the antibiotic regimen chosen. Patients admitted directly from their homes had the least complicated disease course and all survived. A low CSF leucocyte count, mainly found in young patients so admitted, could indicate either a non-bacterial self-limiting aetiology or diagnosis at an early stage of the disease. We found, however, that bacterial meningitis cannot be excluded on the basis of the CSF leucocyte count in combination with any clinical and biochemical parameters. Rapid hospital admission, regardless of age, is of major importance for prognosis. Improvement of non-cultural diagnostics tests and adjunctive therapy regimens are essential.