CLINICAL DESCRIPTION
A mosquito-borne viral illness of variable severity, characterized by sudden onset, fever, relatively slow pulse, headache, generalized muscle pain, and jaundice. Most infections resolve at this stage. After a brief remission of hours to a day, some cases progress into the ominous stage of intoxication and liver and renal failure.

CASE CLASSIFICATION

1. CONFIRMED
   
   A clinically compatible case, AND:
• Demonstration of fourfold or greater rise in yellow fever antibody titer in a patient who has no history of recent yellow fever vaccination and cross-reactions to other flaviviruses have been excluded, OR
  
• Demonstration of yellow fever virus, antigen or genome in tissue, blood or other body fluid.
  
  
2. PROBABLE
   
   A clinically compatible case, AND:
• Demonstration of stable elevated antibody titer to yellow fever virus (equal to or greater than 32 by complement fixation, 256 by immunofluorescence assay, 320 by hemagglutination inhibition, 160 by neutralization, or a positive serologic results by immunoglobulin M-capture enzyme immunoassay).
  
• Cross-reactive serologic reactions to other flaviviruses must be excluded, and the patient must not have a history of yellow fever vaccination.
  
  
3. POSSIBLE
   
   Not used