title: Beyond viruses: clinical profiles and etiologies associated with encephalitis.
abstract: 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.
authors.affiliation: Viral and Rickettsial Disease Laboratory, California Department of Health Services, Richmond, CA 94804, USA. cglaser@dhs.ca.gov
authors.forename: C A
authors.initials: CA
authors.lastname: Glaser
authors.forename: S
authors.initials: S
authors.lastname: Honarmand
authors.forename: L J
authors.initials: LJ
authors.lastname: Anderson
authors.forename: D P
authors.initials: DP
authors.lastname: Schnurr
authors.forename: B
authors.initials: B
authors.lastname: Forghani
authors.forename: C K
authors.initials: CK
authors.lastname: Cossen
authors.forename: F L
authors.initials: FL
authors.lastname: Schuster
authors.forename: L J
authors.initials: LJ
authors.lastname: Christie
authors.forename: J H
authors.initials: JH
authors.lastname: Tureen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D004660:Encephalitis / Q000382:microbiology / Q000503:physiopathology* / Q000821:virology; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D012107:Research Design / Q000592:standards*; D013577:Syndrome; D014780:Viruses / Q000302:isolation & purification