This document gives recommendations to EU/EEA Member States on testing, typing and subtyping to identify zoonotic influenza virus infections in humans during the influenza season, 2024?2025 in the European Union/European Economic Area (EU/EEA). The recent detection of a human case of avian influenza A(H5N1) in Missouri, United States through the state’s surveillance system for seasonal influenza emphasises the importance of influenza virus typing, subtyping and further virus characterisation.

Raising awareness among healthcare workers (in primary and secondary care)

In areas where outbreaks of avian influenza in birds or mammals have occurred, there is a possibility that there may be human cases of zoonotic influenza infection with unknown exposure and therefore public health authorities should encourage laboratories and hospitals/clinicians to consider increasing testing for influenza, typing and subtyping.
Raising awareness should include communicating the local epidemiological situation, including avian influenza in birds and animals, to healthcare workers (including primary care workers) in the region.
In order not to miss or delay diagnosis of potential human zoonotic influenza cases, healthcare workers should ask patients about any symptoms compatible with zoonotic influenza infection and their history of exposure to animals, particularly in the context of any ongoing avian influenza outbreaks in birds or mammals.
Testing of exposed persons to infected animals with zoonotic influenza

Persons exposed to zoonotic influenza should be monitored for 10?14 days from last day of exposure.
If exposed individuals develop symptoms, they should self-isolate and be tested immediately.
Asymptomatic individuals who have been exposed to zoonotic influenza may be tested on a case-by-case basis, taking into account the level of exposure and the epidemiological context.
Testing, typing and subtyping for influenza in hospital settings

Patients admitted to hospital with respiratory symptoms or other symptoms compatible with avian influenza virus infection should be asked about their history of exposure to animals potentially infected with avian influenza or other sick/dead animals.
Patients admitted to hospital due to respiratory or other influenza-related symptoms should be tested for influenza A/B infection in accordance with a clinical decision, including subtyping. Decisions on who to test and type/subtype should take into account the epidemiological situation (e.g. avian influenza outbreaks in the area) and the risk of exposure and be linked to a national risk assessment. As the avian influenza epidemiological situation is dynamic, ECDC is continuously re-assessing the risk and will update the risk assessment as necessary in the quarterly ECDC/EFSA avian influenza monitoring report.
It is recommended that all hospitalised patients with unexplained viral encephalitis/meningoencephalitis in whom an alternative causative agent cannot be identified should be tested for influenza virus. Isolates from patients who test positive for influenza A should then be subtyped to rule out zoonotic influenza.
Severely ill patients with unexplained illness who have had prior animal exposure should be considered for influenza virus testing and further typing/subtyping if they test positive for influenza A.
Clusters of severe respiratory infections requiring hospitalisation should be investigated, and patients should be tested for zoonotic influenza if routine testing/subtyping for respiratory pathogens is inconclusive, or if they test positive for influenza A which cannot be subtyped.
Influenza testing in specimens from sentinel ILI/ARI/SARI surveillance sources

Ideally, all sentinel influenza-positive specimens from both primary and secondary care sentinel sources should be typed and subtyped.
Influenza testing in specimens from other sources (including non-sentinel)

If there are known avian influenza outbreaks in birds or mammals in the area, even in the absence of known exposure to infected animals, laboratories/clinicians are encouraged to increase typing and subtyping of influenza-A positive cases.
Wastewater surveillance

Wastewater surveillance is currently emerging as a novel surveillance tool to detect low-level circulation of avian influenza viruses due to outbreaks in birds or mammals, with studies mainly originating from the national system in the US.
In the EU/EEA, wastewater surveillance for influenza is currently being conducted in six EU/EEA countries (see reference 38), and additional countries have expressed interest in contributing to wastewater surveillance activities related to avian A(H5N1) influenza viruses.
Wastewater surveillance can be used as a potential complementary system useful for the early identification of the presence of circulating avian influenza viruses in specific areas.