Current case definition for zoonotic influenza in humans

This is the case definition for zoonotic influenza, as published in the Official Journal of the European Union (Commission Implementing Regulation (EU) 2026/2097).

Zoonotic influenza

Zoonotic influenza in humans is an infection caused by an influenza virus that is primarily adapted to non-human animal hosts (such as birds, pigs, horses) and is not circulating in the human population but can cause a human infection through direct or indirect exposure to infected animals or contaminated environments.

Clinical Criteria

At least one of the following:

—acute respiratory infection

—influenza-like illness

—Severe acute respiratory infection

—Conjunctivitis;

—Neurological presentation (for example encephalitis);

—Other severe or unusual clinical presentations not explained by an alternative diagnosis.

Laboratory Criteria

At least one of the following:

—Isolation of a zoonotic influenza virus from a clinical specimen;

—Specific antibody response to a zoonotic influenza virus (four-fold or greater rise);

—Detection of a zoonotic influenza virus nucleic acid in a clinical specimen (in case of nucleic acid positivity only, clinical, and/or epidemiological, and/or other laboratory criteria shall be verified to rule out sample contamination)..

Epidemiological Criteria

In the 14 days prior to symptom onset, at least one of the following:

—Close contact with a probable or confirmed human case of zoonotic influenza;

—Close contact with an animal in which zoonotic influenza A virus has been confirmed;

—Presence in a setting (for example, home, farm, market, workplace) in which zoonotic influenza A virus has been confirmed in animals or the environment;

—Laboratory exposure to zoonotic influenza virus.

Case Classification

A. Possible case NA

B.Probable case:

Any person meeting the clinical AND the epidemiological criteria

OR

Any person meeting the epidemiological criteria AND detection of unsubtyped non-seasonal influenza A – (pending confirmation).

C. Confirmed case:

Any person meeting the laboratory criteria (laboratory confirmation performed by a national reference laboratory for influenza or European Union reference laboratory or WHO Collaborating Centre or other WHO reference laboratory.).