Guidance

Avian influenza A(H7N4): risk assessment

Updated 17 July 2020

UK Health Security Agency’s risk assessment for H7N4

Update July 2020: all risk assessments are reviewed regularly, but are not updated unless there is a significant epidemiological development or change in risk. Since the initial report of this case, in April 2018, no further cases have been reported.

Description of incident

A 68-year-old woman with coronary heart disease and hypertension from Jiangsu province, China, developed severe pneumonia and was admitted to hospital on 1 January 2018. The individual survived their illness and was discharged after 21 days. A throat swab specimen was taken from the patient and tested by real-time RT-PCR and sequencing; these tests detected influenza A(H7N4). The individual’s close contacts (28 in total) were monitored and did not report symptoms. Throat swabs taken from the same group tested negative.

Investigation of source

The individual had slaughtered poultry during the putative incubation period, prior to the onset of illness. Ducks and chickens on the same premises were investigated and tested positive for low pathogenicity avian influenza A(H7N4). There is presently insufficient information about whether this virus is found in other poultry in China. There have been previous unrelated avian influenza A(H7N4) outbreaks in Australia (1997) and the Netherlands (2010).

Virological information

Sequencing information related to the specimen from the human case showed that the virus is genetically similar to avian influenza viruses that are circulating in wild birds. Sequencing also demonstrated that the HA gene was distinct from that seen in A(H7N9) viruses circulating in China. Sequencing did not identify any known mutations associated with reduced susceptibility to antiviral medicines such as neuraminidase inhibitors (for example, oseltamivir). There was one marker associated with mammalian adaptation (627K at PB2). The World Health Organization (WHO) has not recommended the development of a candidate vaccine virus (CVV). No sequence information has been published in the GISAID database to date.

Overall summary

Internal gene reassortments are to be expected among wildfowl and it would be expected that there may be sporadic assortments in animal hosts. Depending on exposures to poultry, there may be sporadic infections in humans.

Risk assessment

The risk to UK residents in the UK from avian influenza A(H7N4) is very low, as there is no known animal reservoir in the UK.

The risk of avian influenza A(H7N4) to UK residents travelling to mainland China is low, but would be higher in those individuals with a history of poultry exposure and associated activities.

The probability that a cluster of severe acute respiratory illness in the UK is due to avian influenza A(H7N4) is very low, but testing would be indicated. A history of travel to mainland China would increase this probability.

If compliance with infection control guidance is good, the risk to healthcare workers caring for any cases of A(H7N4) is very low. However, any respiratory illness among healthcare workers undertaking this work would be rapidly investigated for this infection.

The risk of infection to contacts of laboratory-confirmed cases of avian influenza A(H7N4) is currently considered low. Such individuals would be subject to public health follow-up following their exposure, however, and tested for infection if they developed any new febrile or respiratory illness.

Travel advice

To help reduce the risk of infection, the National Travel Health Network and Centre (NaTHNaC) advised travellers visiting China or other areas affected by avian influenza to:

• 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
• not eat or handle undercooked or raw poultry, egg or duck dishes
• not pick up or touch dead or dying birds
• not attempt to bring any poultry products back to the UK
• maintain good personal hygiene with regular handwashing with soap
• use alcohol-based hand rubs

Travellers to China or other affected areas should be alert to the development of signs and symptoms of influenza for 10 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 infections. 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.

Testing

Testing of avian influenza A(H7N4) should be arranged urgently if an individual meets at least one criterion from Part A and at least one criterion from Part B.

Part A

• fever ≥ 38°C and clinical or radiological findings of consolidation/ARDS and/or
• other illness suggestive of an infectious process

Part B

• the patient has visited mainland China in the 10 days before the onset of symptoms and/or
• the patient has had close contact with a confirmed case of avian influenza A(H7N4) in the 10 days before symptom onset

In addition, any returning traveller from mainland China who meets the above criteria should also be considered against the criteria for avian influenza A(H7N9) and avian influenza A(H5) infections.

Further guidance on public health investigation and arranging laboratory testing for avian influenza is available.

Sources

1. WHO: Human infection with avian influenza A(H7N4) virus – China, 22 February 2018.
2. ECDC: Communicable disease threats report: Week 7, 11 to 17 February 2018.
3. WHO: Antigenic and genetic characteristics of zoonotic influenza viruses and candidate vaccine viruses developed for potential use in human vaccines, 22 February 2018.