Encephalitis is associated with significant mortality and morbidity, but its cause remains largely unknown. We designed a national prospective study in France in 2007 to describe patients with encephalitis, investigate the etiologic diagnosis of encephalitis, and assess risk factors associated with death. Patients were enrolled by attending physicians according to case definition, and data were collected with a standardized questionnaire. The etiologic diagnosis was investigated after a standardized procedure. Risk factors associated with death during hospitalization were assessed by multivariate logistic regression. A total of 253 patients with acute infectious encephalitis from 106 medical units throughout France were included in the study. Their ages ranged from 1 month to 89 years (median age, 54 years); 61% were male. Cause of the encephalitis was determined in 131 patients (52%). Herpes simplex virus 1 (42%), varicella-zoster virus (15%), Mycobacterium tuberculosis (15%), and Listeria monocytogenes (10%) were the most frequently identified agents. Twenty-six patients (10%, all adults) died, 6 of them with tuberculosis and 6 with listeriosis. Risk factors independently associated with death during hospitalization identified by the multivariable analysis were age (odds ratio [OR], 1.2; 95% confidence interval [CI], 1.0-1.4; for 5-year increase), cancer (OR, 17; 95% CI, 2.3-122.6), immunosuppressive treatment before onset (OR, 24; 95% CI, 1.3-426.0), percentage of hospitalized patients receiving mechanical ventilation (OR, 2.0; 95% CI, 1.4-3.0; for 10% increase), the etiologic agent, coma on day 5 after admission (OR, 16; 95% CI, 2.8-92.3), and sepsis on day 5 after admission (OR, 94; 95% CI, 4.9-1792.2). Our prospective study provides an overview of the clinical and etiologic patterns of acute infectious encephalitis in adults in France. Herpes simplex virus 1 remains the main cause of encephalitis, but bacteria accounts for the highest case-fatality rates.
