Guidance

Risk assessment of avian influenza A(H5N1): fourth update

Updated 31 January 2023

Background

From 2003 until 25 November 2022, 868 confirmed human cases and 457 deaths due to avian influenza A(H5N1) had been reported to the World Health Organization (WHO) from 21 countries.^{[footnote 1]}

Highly pathogenic avian influenza (HPAI) A(H5N1) was first reported in the Far East, but is now enzootic in poultry across Asia and Africa. Although there have been very few human cases of A(H5N1) reported since 2015, outbreaks of HPAI A(H5N1) have occurred among poultry in several countries across Africa, America, Europe and Asia.^{[footnote 2]}

The vast majority of human cases have reported contact with poultry and there is no reported evidence of sustained human-to-human transmission. No major changes have been detected in recently characterised viruses from human cases.

Risk assessment

The risk of influenza A(H5N1) infection to UK residents within the UK is very low.

The risk of influenza A(H5N1) infection to UK residents who are travelling to affected areas is very low, but may be higher in those with exposure to specific risk factors within the region, such as poultry.

The level of risk of influenza A(H5N1) infection in those who arrive in the UK from affected areas and meet the case definition is low, but warrants testing.

The probability that a cluster of cases of severe respiratory illness in the UK is due to influenza A(H5N1) is very low, but warrants testing. A history of travel to affected areas would increase the likelihood of influenza A(H5N1).

If there is good compliance with guidance on infection control measures, the risk to healthcare workers caring for cases of influenza A(H5N1) in the UK is very low. However, febrile or respiratory illness in healthcare workers caring for cases of influenza A(H5N1) warrants testing.

The risk to contacts of confirmed cases of influenza A(H5N1) infection is low, but warrants follow-up in the 7 days following exposure and urgent investigation of any new febrile or respiratory illness.

Advice for travellers

No specific restrictions to travel are advised. However, to help reduce the risk of infection, NaTHNaC advises that travellers:

• avoid close or direct contact with live poultry
• avoid visiting live bird and animal markets (including ‘wet’ markets) and poultry farms
• avoid contact with surfaces contaminated with animal faeces
• avoid untreated bird feathers and other animal and bird waste
• do not eat or handle undercooked or raw poultry, egg or duck dishes
• do not pick up or touch dead or dying birds
• do not attempt to bring any poultry products back to the UK
• maintain good personal hygiene with regular hand washing with soap and use of alcohol-based hand rubs

Travellers to affected areas should be alert to the development of signs and symptoms of influenza for 7 days following their return. It is most likely that anyone developing a mild respiratory tract illness during this time is suffering from seasonal influenza or other commonly circulating respiratory infection. However, if they become concerned about the severity of their symptoms, they should seek appropriate medical advice and inform the treating clinician of their travel history.

Advice for clinicians and health professionals

Clinicians should retain a high level of suspicion of influenza A(H5N1) when managing patients with confirmed or suspected influenza A and a history of travel to affected areas in the 7 days before the onset of symptoms.

Guidance on the public health management of possible cases and their contacts is available. Contact the local health protection team to discuss possible cases and testing criteria.

The local UK Health Security Agency (UKHSA) Public Health Laboratory can provide advice on arranging testing for influenza A due to H5/H7.

Case definition for possible cases of A(H5N1)

Clinical criteria

• fever ≥ 38°C

or

• acute respiratory symptoms (cough, hoarseness, nasal discharge or congestion, shortness of breath, sore throat, wheezing or sneezing)

or

• other severe or life-threatening illness suggestive of an infectious process

Additionally, patients must fulfil a condition in either category 1 or 2 of the exposure criteria below.

Exposure criteria

• close contact (within 1 metre) with live, dying or dead domestic poultry or wild birds, including live bird markets, in an area of the world affected by avian influenza** or with any confirmed infected animal, in the 10 days before the onset of symptoms

or

• in the 10 days before the onset of symptoms, close contact* with:
  • a confirmed human case of avian influenza
  • human case(s) of unexplained illness resulting in death from affected areas**
  • human cases of severe unexplained respiratory illness from affected areas**

*This includes handling laboratory specimens from cases without appropriate precautions, or was within 1 metre distance, directly providing care, touching a case or within close vicinity of an aerosol generating procedure, from 1 day prior to symptom onset and for duration of symptoms or positive virological detection.

**See the HCID country list. If unsure, discuss with UKHSA Clinical and Public Health (CPH).

Further reading

1. Cumulative number of confirmed human cases for avian influenza A(H5N1) reported to WHO, 2003 to 2022 (6 January 2023) ↩

2. World Organisation for animal health – avian influenza (27 January 2023) ↩