Key Points
• Influenza or ‘Flu’ is an acute viral infection affecting the respiratory tract. There are three main types or ‘genera’ of viruses that affect humans: Influenza virus A, Influenza virus B and Influenza virus C.
• Influenza A, which can infect many animal species, is the most common and virulent and is usually the cause of flu epidemics. In temperate zones, influenza is typically seasonal with most cases occurring during the winter months.
• This guidance should be followed in conjunction with the guidance in the National Infection Prevention and Control Manual (NHSE 2024) A to Z of Pathogens resource (and references therein) for Endemic and Pandemic influenza.
This is a controlled document. If you are using a printed copy, check it against the guidelines site to ensure you are using the latest edition. Print copies must be destroyed after use.
Abbreviations
1.0 Introduction
Influenza or ‘Flu’ is an acute viral infection affecting the respiratory tract. There are three main types or ‘genera’ of viruses that affect humans: Influenza virus A, Influenza virus B and Influenza virus C.
Influenza A, which can infect many animal species, is the most common and virulent and is usually the cause of flu epidemics. In temperate zones, influenza is typically seasonal with most cases occurring during the winter months.
This guidance should be followed in conjunction with the guidance in the National Infection Prevention and Control Manual (NHSE 2024) A to Z of Pathogens resource for Endemic and Pandemic influenza.
2.0 Influenza Symptoms
Influenza symptoms often have a sudden onset, and can include:
• a sudden high temperature
• an aching body
• feeling tired or exhausted
• a dry cough
• a sore throat
• a headache
• difficulty sleeping
• loss of appetite
• diarrhoea or tummy pain
• feeling sick and being sick
The symptoms are similar for children, with the addition of ear pain and appearing less active.
Vulnerable group are at a higher risk of complications (such as bronchitis and pneumonia) include children, elderly, individuals who are morbidly obese, those with chronic medical conditions (such as diabetes and COPD), and those who are immunocompromised.
The incubation period ranges between 1-3 days, with cases being infectious from one day before, to five days after symptom-onset.
Influenza is transmitted by breathing in droplets coughed out into the air by infected people or by the droplets landing on mucous membranes. Transmission may also occur by direct or indirect contact with respiratory secretions for example via soiled tissues or from contaminated surfaces. It spreads easily in crowded populations (such as acute hospital environments) and in enclosed spaces.
People with asymptomatic infections are likely to be infectious to some extent and transmit it.
Experiments have demonstrated that Influenza ‘A’ viruses can survive:
• Up to 72 hours (only small quantities were detectable beyond 48 hours) on hard surfaces (stainless steel counter, plastic wash bowl)
• Up to 24 hours (only small quantities were detectable after 12 hours) on soft material (pyjamas, handkerchiefs)
• Up to 5 minutes on hands.
3.0 Categories Of Influenza
3.1 Seasonal/ Endemic Influenza
Seasonal (endemic) influenza most often occurs in the winter months, with prevalence peaking between December and March, and is most often caused by the circulating strains of influenza A and B.
Influenza A is the most common and virulent and is usually the cause of influenza epidemics.
3.1.1 Infection Prevention – Vaccination
The best way to reduce risk of infection, is through vaccination.
Trust staff are actively encouraged to take up the seasonal influenza vaccination offered every year, as circulating strains vary from year to year.
Staff should make every contact count and encourage and promote vaccination in eligible patient groups.
For more information about influenza vaccination, refer to the Green Book (UKHSA 2023) Chapter 19.
3.1.3 Infection Prevention – Post-Exposure Prophylaxis
Refer to the Trust Microguide for guidance on prophylaxis of inpatients exposed to influenza. Prophylaxis is advised if the contact is not adequately protected by vaccination, for example, if there has been less than 14 days between vaccination and date of exposure (UKHSA 2021).
3.1.4 Management of Seasonal Influenza Cases
3.2 Avian Influenza
Avian influenza includes a group of influenza A strains which affect birds. The majority of these viruses do not infect humans, however on rare occasions they can infect other animals including humans.
Avian influenza H7N9, H9N2, H5N1, and H5N6 are categorised as airborne High Consequence Infectious Diseases (HCID).
3.2.1 Clinical presentation
For H7N9, H9N2, H5N1, H5N6 and any other avian influenza associated with severe human disease:
- 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.
** For H7N9, H5N1 and H5N6 see the HCID country list. For H9N2, affected areas include China and Oman.
3.2.2 Management of Avian Influenza Cases
3.3 Pandemic influenza
Pandemic influenza is a global outbreak of a novel influenza A virus strain. Influenza pandemics are uncommon but serious, as:
• the virus can spread quickly due to lack of immunity to the novel strain in the population,
• immediate vaccination might not be available, and
• large numbers of cases worldwide can cause an excessive burden on healthcare services, as well as education and businesses/ economy.
The most recent influenza pandemic was the 2009/10 ‘Swine flu’ pandemic, which was caused by the influenza A strain H1N1.
Pandemics have the potential to be caused by other non-human influenza A viruses, such as those causing Avian Influenza.
The guidance for the infection prevention and control management of seasonal influenza (section 3.1.4) should be followed, in addition to any national guidance released in the event of a pandemic, for the specific influenza strain associated for the pandemic.
4.0 Monitoring:
Monitoring of practices in line with this guidance, is carried out by the Infection Prevention & Control Team as part of clinical ward rounds, audit, and surveillance.
In the event of the occurrence of Pandemic Influenza cases, this document would be monitored as part of the Major Incident monitoring process.
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This guideline has been registered with the Trust. However, clinical guidelines are guidelines only. The interpretation and application of clinical guidelines will remain the responsibility of the individual clinician. If in doubt, contact a senior colleague or expert. Caution is advised when using guidelines after the review date.
This guideline is for use in Frimley Health NHS Foundation Trust hospitals only. Any use outside this location will not be supported by the Trust and will be at the risk of the individual using it.
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