Journal Article

Beyond Viruses: Clinical Profiles and Etiologies Associated with Encephalitis

C. A. Glaser, S. Honarmand, L. J. Anderson, D. P. Schnurr, B. Forghani, C. K. Cossen, F. L. Schuster, L. J. Christie and J. H. Tureen

in Clinical Infectious Diseases

Published on behalf of Infectious Diseases Society of America

Volume 43, issue 12, pages 1565-1577
Published in print December 2006 | ISSN: 1058-4838
Published online December 2006 | e-ISSN: 1537-6591 | DOI:
Beyond Viruses: Clinical Profiles and Etiologies Associated with Encephalitis

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Background. Encephalitis is a complex syndrome, and its etiology is often not identified. The California Encephalitis Project was initiated in 1998 to identify the causes and further describe the clinical and epidemiologic characteristics of encephalitis.

Methods.A standardized report form was used to collect demographic and clinical data. Serum, cerebrospinal fluid, and respiratory specimens were obtained prospectively and were tested for the presence of herpesviruses, arboviruses, enteroviruses, measles, respiratory viruses, Chlamydia species, and Mycoplasma pneumoniae. The association between an identified infection and encephalitis was defined using predetermined, organism-specific criteria for confirmed, probable, or possible causes.

Results. From 1998 through 2005, a total of 1570 patients were enrolled. Given the large number of patients, subgroups of patients with similar clinical characteristics and laboratory findings were identified. Ten clinical profiles were described. A confirmed or probable etiologic agent was identified for 16% of cases of encephalitis: 69% of these agents were viral; 20%, bacterial; 7%, prion; 3%, parasitic; and 1%, fungal. An additional 13% of cases had a possible etiology identified. Many of the agents classified as possible causes are suspected but have not yet been definitively demonstrated to cause encephalitis; these agents include M. pneumoniae (n = 96), influenza virus (n = 22), adenovirus (n = 14), Chlamydia species (n = 10), and human metapneumovirus (n = 4). A noninfectious etiology was identified for 8% of cases, and no etiology was found for 63% of cases.

Conclusions. Although the etiology of encephalitis remains unknown in most cases, the recognition of discrete clinical profiles among patients with encephalitis should help focus our efforts toward understanding the etiology, pathogenesis, course, and management of this complex syndrome.

Journal Article.  5126 words.  Illustrated.

Subjects: Infectious Diseases ; Immunology ; Public Health and Epidemiology ; Microbiology

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