Case definition for surveillance of Zika virus infection

This case definition was published in Commission Implementing Regulation (EU) 2026/2097, which lists the diseases and health issues under EU surveillance.

Definition

Clinical criteria 

Clinical manifestations compatible with Zika virus disease (for example, rash, fever, a foetus or newborn with microcephaly or intracranial calcifications or other central nervous system abnormalities).

Laboratory criteria

Probable case 

Detection of anti-Zika virus IgM antibodies in a single serum sample. 

Confirmed case 

At least one of the following five: 

  • Isolation and identification of Zika virus from a clinical specimen; 
  • Detection of Zika virus nucleic acid in a clinical specimen; — Detection of Zika virus antigen in a clinical specimen; 
  • Detection of acute infection through serological methods (for example, IgM antibodies in a single serum sample, seroconversion or four-fold antibody titre increase in paired serum samples, low-avidity IgG antibodies in a serum sample), AND confirmation of the specificity of antibodies by simultaneous neutralisation assays with serologically cross-reacting viruses, or with another equivalently discriminatory method; 
  • Detection of anti-Zika virus IgM antibodies in amniotic fluid or cerebrospinal fluid of a foetus or newborn with microcephaly or intracranial calcifications or other central nervous system abnormalities.

Epidemiological criteria  

At least one of the following four: 

  • Residing in, or having visited within the two-week period prior to the onset of symptoms, an area where Zika virus transmission has previously been detected; 
  • Having received substances of human origin from a donor who has resided or visited (within the four-week period before donation) an area where Zika virus transmission has previously been detected; 
  • Sexual contact within the two-week period prior to the onset of symptoms with a probable or confirmed case of Zika virus infection; 
  • Mother having had a probable or confirmed Zika virus infection during pregnancy

Case Classification

A. Possible case NA 

B. Probable case 
A person meeting the laboratory criteria for a probable case AND the clinical criteria AND the epidemiological criteria 

OR 

A foetus or newborn with microcephaly or intracranial calcifications or other central nervous system abnormalities with a mother meeting at least one of the epidemiological criteria. 

C. Confirmed case 
A person meeting the laboratory criteria for a confirmed case. 

Note: Serological results should be interpreted according to previous exposure to other flaviviral infections and the flavivirus vaccination status.

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