Community-acquired bacterial meningitis: Risk stratification for adverse clinical outcome and effect of antibiotic timing

Background: Community-acquired bacterial meningitis causes substantial morb idity and mortality in adults. Objective: To create and test a prognostic model for persons with community -acquired bacterial meningitis and to determine whether antibiotic timing i nfluences clinical outcome. Design: Retrospective cohort study; patients were divided into derivation a nd validation samples. Setting: Four hospitals in Connecticut. Patients: 269 persons who, between 1970 and 1995, had community-acquired ba cterial meningitis microbiologically proven by a lumbar puncture done withi n 24 hours of presentation in the emergency department. Measurements: Baseline clinical and laboratory features and times of arriva l in the emergency department, performance of lumbar puncture, and administ ration of antibiotics. The target end point was the development of an adver se clinical outcome (death or neurologic deficit at discharge). Results: For the total group, the hospital mortality rate was 27%. Fifty-si x of 269 patients (21%) developed a neurologic deficit, and in 9% the neuro logic deficit persisted at discharge. Three baseline clinical features (hyp otension, altered mental status, and seizures) were independently associate d with adverse clinical outcome and were used to create a prognostic model from the derivation sample. The prediction accuracy of the model was determ ined by using the concordance index (c-index). For both the derivation samp le (c-index, 0.73 [95% CI, 0.65 to 0.81]) and the validation sample (c-inde x, 0.81 [CI, 0.71 to 0.92]), the model predicted adverse clinical outcome s ignificantly better than chance. For the total group, the model stratified patients into three prognostic stages: low risk for adverse clinical outcom e (9%; stage I), intermediate risk (33%; stage II), and high risk (56%; sta ge III) (P = 0.001). Adverse clinical outcome was more common for patients in whom the prognostic stage advanced from low risk (P = 0.008) or intermed iate risk (P = 0.003) at arrival in the emergency department to high risk b efore administration of antibiotics. Conclusions: In persons with community-acquired bacterial meningitis, three baseline clinical features of disease severity predicted adverse clinical outcome and stratified patients into three stages of prognostic severity. D elay in therapy after arrival in the emergency department was associated wi th adverse clinical outcome when the patient's condition advanced to the hi ghest stage of prognostic severity before the initial antibiotic dose was g iven.