Case Definition

 Confirmed Case

Clinical illness¹ with laboratory confirmation of infection:

• isolation of yellow fever virus;
  

OR

• detection of yellow fever viral antigen or nucleic acid in body fluids or tissue;

OR

• a significant (e.g. fourfold or greater) rise in antibody titre to the yellow fever virus or a single elevated yellow fever IgM antibody titre in the absence of yellow fever vaccination within the previous 2 months.
  

Probable Case²

Clinical illness with a stable elevated antibody titre to yellow fever virus with no other known cause.

Notes:

1. Clinical illness: a mosquito-borne viral illness characterized by acute onset and constitutional symptoms followed by a brief remission and a recurrence of fever, hepatitis, albuminuria, and in some instances, renal failure, shock, and generalized hemorrhages.
   
2. For probable cases, cross-reactive serologic reactions to other flaviviruses must be excluded, and the patient must not have a history of yellow fever vaccination.