Guidance

Guidance for the management of people exposed to birds or other animals infected with influenza A(H5)

Updated 15 January 2026

This guidance covers:

• bird and other animal case definitions
• types of human exposure to infected birds or other animals, and the management of those individuals
• personal protective equipment (PPE), testing, antiviral use, and principles for health protection teams (HPTs)

1. Background and purpose

This guidance is for clinical and public health professionals responding to humans exposed to influenza A(H5) in birds or other animals.

Check this page regularly for updates, including changes to recommendations in this guidance.

Influenza A(H5) is currently circulating in birds and has caused mammalian outbreaks and human zoonotic infections globally. Due to reassortment with other avian viruses, there are many genotypes, some of which have distinct properties. There is also the potential for mutations to be acquired which facilitate changes in the virus profile or host range.    

Following a new process approved by the Advisory Committee on Dangerous Pathogens (ACDP), a joint UK Health Security Agency (UKHSA), Animal and Plant Health Agency (APHA), and Department for Environment, Food and Rural Affairs (DEFRA) risk assessment will be undertaken at the start of each avian influenza season using available genomic, laboratory, and epidemiological data on influenza A(H5) viruses circulating in Europe and early seasonal wild bird detections in the UK. The risk assessment will guide the approach to the public health response to human exposures to birds or other animals infected with influenza A(H5) and associated premises for the season.

If there are no signals of increased risk associated with the viruses circulating (such as frequent genomic features associated with mammalian adaptation, or a high rate of zoonotic cases previously associated with the same virus) in the risk assessment, this guidance document will cover the management of humans exposed to influenza A(H5) in birds or other animals and infected premises.

If there are any features of a higher risk virus being detected or the situation changes suggestive of an increased risk in the risk assessment, this guidance document would not apply. Instead, the ‘strict approach’ in which antivirals are offered to all those in contact with affected birds or other animals and infected premises, regardless of use of PPE use, should then be used as an additional safeguard.

If the situation changes during the avian influenza season, the risk assessment will be revisited.

2.  Principles of prevention of human infection with influenza A(H5)

In situations where influenza A(H5) is suspected or confirmed in infected premises the following principles should apply:

• keep the number of people exposed to the infected birds or animals and premises to a reasonable minimum; this may need to be balanced against the need to undertake necessary control measures
• reduce human risk by limiting the number of individuals required to enter infected premises for occupational reasons (such as for collection or disposal of birds or animals, and cleaning or decontamination) and those that should have access to the premises
• ensure that people who are likely to be exposed as responders (and therefore have the potential to become exposed individuals) are advised and trained on the appropriate and safe use of PPE, including donning and doffing, and should be fit-tested where appropriate

For working with suspected or confirmed infected poultry, the appropriate PPE is set out by the Health and Safety Executive (HSE).

Subject to a local risk assessment undertaken by the employer, elements of this guidance may be relevant to work with other farm animals or in other agricultural settings.

Clinical and public health professionals should provide with information on influenza A(H5) to all exposed individuals, including what to do if they develop symptoms of infection.

Start antiviral post-exposure prophylaxis as soon as possible after exposure, where indicated.

The advice for members of the public is not to touch sick or dead wild birds – where removal and disposal of dead wild birds is unavoidable, individuals should follow the advice in Avian influenza (bird flu): advice for the public to reduce the risk of catching avian influenza.

3. Animal case definitions: influenza A(H5)

The APHA has published detailed guidance on suspect case definitions, diagnostic criteria and testing in mammals, which should be used by HPTs in conjunction with the case definitions below in Table 1. The influenza A(H5) case definitions for birds and other animals below are for influenza A(H5N1) but can be used for other H5 subtypes. They may be updated or expanded if the evidence changes, so it is important to regularly refer to this page when using this guidance. The APHA Surveillance for Avian Influenza in Wild Birds and Wild Mammals in GB map can be used to inform HPTs where positive wild birds and animals are found, or where mass mortality events are reported in wild birds, as not all may have been tested.

Table 1. Infected bird and other animal definitions: influenza A(H5) (for use during avian influenza season, or in a restriction zone in or out of season)

Infected animal and premises definitions	Animal clinical definitions	Laboratory test results
Probable infection: wild (non-domestic) bird species, mammal or genus which is listed as affected by influenza A(H5) by APHA	Dead or clinical signs suggestive of infection with influenza A(H5) during avian flu season and informed by the extant wild bird risk level, or APHA advises should be treated as a probable case regardless of whether testing will be undertaken	Test results unavailable
Confirmed infection: individual bird or other animal, either domestic or non-domestic	Clinical signs suggestive of infection with influenza A(H5) based on clinical case definitions	Positive for presence of influenza A(H5Nx) virus (notifiable avian disease)
Infected premises: may include poultry, other non-domestic or domestic birds, or other animals	Clinical signs suggestive of infection with influenza A(H5) based on clinical case definitions	APHA have declared an infected premises following a positive influenza A(H5) result (PCR) from clinical samples of an animal in a herd/flock Chief Veterinary Officer has confirmed presence of disease

Note: Information on avian influenza in mammals is available from Influenza A(H5N1) infection in mammals: suspect case definition and diagnostic testing criteria.

4. Human exposure to influenza A(H5) from a zoonotic source

HPTs should assess people potentially exposed to avian influenza A(H5) using Table 2 and classify them as having either high or low risk exposure (or not exposed). APHA can provide an infectious period estimate for the birds or other animals. When an influenza A(H5) infection has been confirmed in poultry, a minimum of a 3km protection zone is put in place around the infected premises by APHA or DEFRA. These are refreshed on the notifiable animal disease cases and zones site.

HPTs should consider the examples provided as principles when carrying out risk assessments.

Contact acute.respiratory@ukhsa.gov.uk, or the Epidemic and Emerging Infections (EEI) consultant on-call (out of hours details circulated with the UKHSA Out of Hours rota) for support, or where consensus cannot be reached locally.

Table 2. Human exposure to infected birds or other animals: influenza A(H5)

The table below classifies the types of human exposure (high or low) to confirmed or probable infected birds or other animals (captive or wild), and confirmed or suspected infected premises, with influenza A(H5) as defined in Table 1.

Exposure risk	Description	Examples
High: unprotected physical or direct contact or likely respiratory exposure	An individual not wearing full PPE as set out by HSE, or who has had a breach in PPE use, who undertakes one or more of the examples	Close or direct contact [note 1] with confirmed or probable infected birds or other animals (captive or wild) [note 2] Close or direct exposure to the contaminated environment [note 3] of infected birds or other animals Close or direct exposure to contaminated materials from confirmed or probable infected birds or other animals, for example faecal material, animal produce, including eggs, milking equipment or during poultry rendering
Low: protected physical or respiratory exposure	Individual wearing full PPE as set out by HSE (with no breaches in PPE use) who has close contact with an infected animal or infected premises declared by APHA	Close or direct [note 1] contact with confirmed or probable infected birds or other animals [note 2] Close or direct exposure to the contaminated environment [note 3] of infected birds or other animals Close or direct exposure to contaminated materials from confirmed or probable infected birds or other animals, for example faecal material, animal produce such as eggs, milking equipment, or during poultry rendering
Low: no physical contact, unlikely respiratory exposure	An individual not wearing full PPE as set out by HSE, who undertakes any of the examples	A visit to or work on an infected premises with no contact with infected animals or their contaminated environment, for example walking through an infected premises staying more than 1 metre away from infected animals or contaminated environment [note 3]

Notes

Note 1: close contact is defined here as within 1 metre (aligned with current ECDC advice). Includes veterinary workers, farm workers or people living on the farm, abattoir workers or equivalent (person giving direct care to an animal). 

Note 2: for example, wild birds, poultry, non-domestic, domestic, or mammals.  

Note 3: contaminated environment includes surfaces contaminated with animal or bird parts for example carcasses, internal organs, or faeces from influenza A(H5N1) infected birds or other animals

5.  PPE for working with suspected or infected birds or other animals

The correct use of PPE should reduce exposure risk. However, due to the difficulty in effectively assessing PPE usage and compliance, use of PPE does not completely remove the possibility of exposure or infection.

Recommended PPE when working with poultry is described in the HSE guidance, Avoiding the risk of infection when working with poultry that is suspected of having H5 or H7 notifiable avian influenza.

Individuals working at suspected infected premises should wear PPE at all times. All PPE should be suitable for the wearer and, where appropriate, must be fit-tested to the person.

6. Management of individuals exposed to influenza A(H5) in birds or other animals

HPTs should assess people exposed to infected birds, other animals, or premises should be assessed according to their exposure risk (see Table 2). Depending on the level of exposure, individuals will receive active or passive follow-up and may require antiviral prophylaxis. Clinical and public health professionals should arrange for clinical assessment and testing for individuals that develop symptoms within 14 days of exposure to influenza A(H5) as per section 7.

6.1 High-risk exposure

If the individual has had a high-risk exposure to birds or other animals with influenza A(H5), HPTs should:

• inform exposed person about the risk
• provide active monitoring information leaflet
• carry out active monitoring [note 4] for 14 days following last exposure
• recommend chemoprophylaxis [note 5]

Note 4: this involves daily contact (by text, telephone, or email) to check that the exposed person has not developed any symptoms compatible with avian influenza

Note 5: chemoprophylaxis for high-risk exposures to influenza A(H5):

1. Initiate as soon as possible (ideally within 48 hours) after exposure to the case.

2. Use oseltamivir treatment course 75mg twice daily for 5 days. This recommendation is based on limited data that support higher chemoprophylaxis dosing for avian influenza A(H5N1) virus infection. It aims to reduce the potential for the development of antiviral resistance from receiving once daily chemoprophylaxis.

Antivirals can be started up to 7 days after the last exposure but is likely to be less effective if delayed; rapid access to antivirals should be a priority. For additional guidance on dosage recommendations, such as for those with renal impairment or treatment by age group, see Patient Group Direction (PGD) for the supply of oseltamivir for pre and post exposure of avian influenza.

6.2 Low-risk exposure

If the individual has had a low-risk exposure to birds or other animals with influenza A(H5), HPTs should:

• inform the exposed person about the risk
• provide passive monitoring information leaflet
• carry out passive monitoring for 14 days following last exposure
• advise exposed person that they may continue with normal activities

7. Management of symptomatic individuals who have been exposed to influenza A(H5) in birds or other animals

Clinical and public health professionals should carry out a risk assessment for possible A(H5) infection in any individual who develops signs or symptoms (see section 7.1) of an influenza-like illness (ILI) or conjunctivitis, or any severe infectious illness that does not have a plausible alternative explanation, within 14 days of high or low risk exposure to influenza A(H5).

If the individual or HPT is concerned about their symptoms or they are getting worse, then they should contact NHS 111 and tell them they have been potentially exposed to avian influenza. If the exposed individual becomes seriously unwell and requires urgent medical attention, then they should telephone 999 and tell them they have potentially been exposed to avian influenza.

Influenza A(H5) has been classified as an airborne high consequence infectious disease (HCID) requiring transmission-based-precautions.

Use infection prevention control (IPC) measures as set out in the NHS National Infection Prevention and Control Manual (NIPCM). Use PPE according to the addendum on HCID PPE for acute care settings.

7.1 When to clinically suspect influenza A(H5) in exposed symptomatic individuals

This section provides guidance for clinicians on when to suspect influenza A(H5) in patients who are symptomatic and who have been exposed.

Consider Influenza A(H5) infection when a patient presents with any one or more of the relevant signs or symptoms [note 6], influenza-like illness (ILI) [note 7] or conjunctivitis, or any severe infectious illness that does not have a plausible alternative explanation and close contact (within 1 metre) with one or more of the following in the 14 days before the onset of symptoms:  

• any animal, including birds, suspected or confirmed as having avian influenza including infected premises and/or live bird markets in an area of the world (including within the UK) affected by avian influenza [note 8]  
• secretions from infected animals (respiratory secretions, faeces, unprocessed animal products such as unpasteurised milk)  

Influenza A(H5) infection should also be considered where recommended by the HPT (such as an individual on passive follow up that develops symptoms).

Notes

Note 6: signs and symptoms compatible with influenza may include one or more of:

• acute uncomplicated upper respiratory tract signs and symptoms also referred to as ILI (fever at or above 37.8°C plus cough or sore throat)
• fever or feeling feverish
• cough
• sore throat
• runny or stuffy nose
• muscle or body aches
• headaches
• fatigue
• eye redness (or conjunctivitis)
• shortness of breath or difficulty breathing

Less common signs and symptoms include:

• diarrhoea
• nausea
• vomiting
• seizures
• other severe or life-threatening illness suggestive of an infectious disease process such as multi-organ failure or meningoencephalitis

It is important to remember that infection with influenza viruses, including avian influenza A viruses, does not always cause fever.

Note 7: influenza-like illness (ILI) is defined as fever at or above 37.8°C and cough or sore throat. Where the index of suspicion is raised due to exposure or comorbidity, clinical and public health professionals should assess atypical presentations on a case-by-case basis.

Note 8: check the UKHSA list of HCID country-specific risks. If unsure, discuss with UKHSA TARZET Acute Respiratory Team acute.respiratory@ukhsa.gov.uk in hours or the Epidemic and Emerging Infectious (EEI) consultant on call (out of hours details circulated with the UKHSA Out of Hours rota).

See Managing sporadic avian influenza human spillover cases and their contacts in England for when clinicians should suspect avian influenza in symptomatic patients with:

• exposure to a confirmed human case of avian influenza or their infectious secretions
• human cases of unexplained illness resulting in death from affected areas [note 8]
• human cases of severe unexplained respiratory illness from affected areas [note 8]

7.2 What to do when you suspect an Influenza A(H5) infection

For a suspected Influenza A(H5) infection in an exposed symptomatic individual, clinicians should manage the patient as an HCID case until proven otherwise. The clinical team should carry out the initial assessment in strict accordance with the trust’s established HCID Assessment Pathway Protocol.

This protocol aligns the required steps, documentation, and escalation procedures to ensure accurate risk assessment, timely intervention and compliance with national and local guidelines.

Clinical assessment

Clinical assessment should take place in an acute NHS setting or via locally agreed or commissioned services.

Before carrying out an in-person clinical assessment:

• isolate the patient in a single occupancy room, preferably a respiratory isolation room and ideally under negative pressure; positive pressure rooms must not be used
• minimise patient contact to staff and other patients and ask the patient to wear a surgical mask when outside the room
• ensure transmission-based-precautions and PPE (including donning and doffing procedures), as outlined in the NIPCM addendum on HCID PPE – start oseltamivir treatment as per the British National Formulary (BNF)

The local clinician or microbiologist should:

• contact the duty microbiologist or virologist at the nearest regional UKHSA Clinical Network Laboratory (CNL - previously known as the Public Health Laboratory) to discuss sampling and testing arrangements
• if the CNL duty microbiologist or virologist agrees that testing is indicated, follow the laboratory investigations algorithm and notify the local HPT

HPTs should:

• arrange immediate clinical assessment and diagnostic testing [note 9]
• recommend antiviral treatment
• advise the person to self-isolate [note 10] for 14 days following onset of symptoms
• complete the Zoonotic Influenza Enhanced Surveillance Questionnaire and send to acute.respiratory@ukhsa.gov.uk

Note 9: arrange diagnostic nose and throat swab if any respiratory symptoms develop and diagnostic conjunctival swab if conjunctivitis symptoms develop.

Note 10: Clinical and public health professionals should advise individuals self-isolating at home to:

• self-isolate in private accommodation, unless an alternative has been agreed with UKHSA 
• avoid contact with other household members 
• not share towels, bed linen, toothbrushes or eating and drinking utensils such as cutlery or cups 
• not go to work, school or public areas

8. Case definitions for public health management (for HPTs)

The case definitions below are provided to support HPTs with the public health management of individuals exposed to influenza A(H5) infected birds or other animals. They should not be used by clinicians to determine which individuals should be assessed for clinical diagnostic testing.

8.1 Case definitions for individuals exposed to influenza A(H5) infected birds or other animals

Possible case 

A possible case is an individual who meets all of the following:

• any high or low risk exposure to an infected bird, other animal, or infected premises in the 14 days prior to symptom onset (see Table 2)
• influenza-like illness (ILI) or conjunctivitis or any severe infectious illness that does not have a plausible alternative explanation
• not yet tested for influenza A or pending a test result

Probable case 

A probable case is an individual who meets all of the following:

• any high or low risk exposure to an infected bird, other animal, or infected premises in the 14 days prior to symptom onset (see Table 2)
• any clinical presentation (symptomatic or asymptomatic)
• influenza A positive but un-subtypable or subtype unavailable in local PCR assays

Confirmed case

A confirmed case (alive or deceased) is an individual, with a positive avian influenza subtype A(H5N1) confirmed by the UKHSA Respiratory Virus Unit (RVU) in any clinical sample.

UKHSA regional labs or NHS labs are only able to detect avian influenza A H5 subtypes, these presumptive positive results will need to be confirmed by RVU.
Epidemiological criteria include persons with recent (within 14 days) high or low level exposure to a confirmed or probable infected bird or other animal or suspected or infected premise.

Historic case: an individual with serological confirmation of influenza A(H5) infection by an appropriate test and sample, who has not tested positive for influenza A(H5) in a molecular laboratory test (PCR and/or sequencing).

Discarded case: an individual who was initially classified as a possible or probable, who tested negative for influenza A(H5) at the UKHSA CNL or Respiratory Virus Unit (RVU) with appropriately timed samples (while likely to be shedding virus – within 5 days of symptom onset or if asymptomatic, within 14 days of last exposure).

Unresolved case: an individual who was initially classified as a possible or probable case who had symptoms but either did not get tested (PCR and or sequencing) or was tested (PCR and or sequencing) but the results were uninterpretable (for example, testing was not conducted within the 14 days after exposure).

9. Diagnostic testing and results

9.1 Laboratory investigations and sample handling

Laboratory investigations, sample transfer instructions including roles for the UKHSA duty doctor microbiologist or virologist, Respiratory Virus Unit (RVU), EEI Consultant and the HPT are outlined in Diagnostic testing for avian influenza A(H5) and other zoonotic influenza viruses.

9.2 Results and repeat sampling

Actions to take by clinical and public health professionals in line with test results are as follows.

Positive influenza A(H5) subtype at UKHSA Clinical Network Laboratory (CNL): 

• isolate and manage as a confirmed case
• UKHSA CNL should discuss with RVU and arrange urgent forwarding of samples to RVU for confirmation
• reserve baseline serum sample; UKHSA CNL will advise on further testing

Influenza A detected but unsubtypable (or subtyping not available) at local laboratory (such as an NHS laboratory) and has relevant exposure for H5 avian influenza:

• isolate and manage as a probable case pending further test results
• ensure 2 samples, collected into Viral Transport Medium (VTM), are sent to a UKHSA CNL for A(H5) subtyping
• if the UKHSA CNL is unable to determine subtype (unsubtypable sample) or avian influenza testing results are inconclusive, UKHSA CNL to contact RVU to discuss results and options for further testing and to arrange forwarding of samples to RVU
• UKHSA CNL to immediately report result to referring laboratory and RVU

Test result is negative in a UKHSA Clinical Network Laboratory (CNL) for influenza A AND H5 subtyping or influenza A detected and subtyped as seasonal A(H3) or A(H1) AND A(H5) negative:

• de-isolate
• provide the patient with standard influenza advice as appropriate including where to seek treatment if indicated
• if new clinical symptoms develop as defined in the case definition within 14 days of last exposure, re-test
• if appropriate samples were obtained and an alternative diagnosis is likely, then A(H5) may be considered excluded. If clinical suspicion remains, including possible non-A(H5) avian influenza, the UKHSA CNL duty microbiologist/virologist should contact the RVU reference laboratory to discuss results and options for further testing