Swine Flu

Synonyms: swine influenza, influenza A/H1N1v.

Swine flu is an influenza A virus most frequently of subtype H1N1, usually found in pigs but can be transferred to humans. Until recently, human-to-human spread was rare.

Influenza viruses often mutate and this new strain has a unique gene segment combination not previously seen. Because this influenza A virus is sufficiently different from previous viruses, the human community initially may have little immunity to it.

The 2009 outbreak began in Mexico but has spread across the world with the first case confirmed in the UK on 27 April 2009. It has now reached pandemic status here - with human-to-human spread causing “community-level outbreaks”, and some deaths. There will be epidemics worldwide with considerable morbidity and mortality.^1,2

Up-to-date incidence data is available from the Health Protection Agency (HPA).³

Symptoms are similar to those of the usual human seasonal influenza infection. The incubation period is thought to be between two and five days, but may be up to seven days.

Clinicians are encouraged to diagnose swine flu based on symptoms if there is a pyrexia (≥ 38 °C), fever or history of fever and flu-like illness (two or more of the following symptoms: cough, sore throat, rhinorrhoea, muscle and joint aches, headache).¹
There may also be fatigue, loss of appetite and sometimes diarrhoea and vomiting.

It is no longer appropriate to test patients in primary care or emergency departments where admission is not required.¹

Testing may be appropriate if patients are hospitalised (for control of symptoms or placing patients with swine flu together) or if there are atypical symptoms where the diagnosis is particularly in doubt.

Follow the current guidance algorithm:^1,4

• Initially manage the patient by telephone where possible - avoid patient coming to surgery.
• Consider patient for antivirals:
  • Give priority to early treatment with antivirals of people in higher risk groups:⁵
    • Chronic lung disease
    • Chronic heart disease
    • Chronic kidney disease
    • Chronic liver disease
    • Chronic neurological disease
    • Immunosuppression (whether caused by disease or treatment)
    • Diabetes mellitus
    • Patients who have had drug treatment for their asthma within the past three years
    • Pregnant women
    • People aged 65 years and older
    • Young children under 5 years old. Children below 1 year of age may be treated with low dose oseltamivir (seek paediatric advice if any concerns).
  • In considering treatment of people aged 5-64 years with no underlying illness, doctors are advised to take a precautionary approach and offer antivirals to patients with symptoms strongly suggestive of swine flu. It is acknowledged that doctors must use their clinical judgement and will not usually choose to offer antivirals in circumstances where there are minor or unrelated respiratory symptoms.
  • Prophylaxis should not usually be offered to contacts of cases unless, for example, a household member has serious underlying health problems or there are other special circumstances.
• If severe or life-threatening illness refer to hospital for further management. Apply algorithm to see whether admission criteria are met - and refer those patients to hospital:⁶
  1. Severe respiratory distress
     • Adult: severe breathlessness, e.g. unable to complete sentences in one breath. Use of accessory muscles, supra-clavicular recession, tracheal tug or feeling of suffocation.
     • Child: lower chest wall indrawing, sternal recession, grunting, or noisy breathing when calm.
  2. Increased respiratory rate measured over at least 30 seconds:
     • Adult: over 30 breaths per minute.
     • Child: ≥ 50 breaths per minute if under 1 year, or ≥ 40 breaths per minute if ≥ 1 year.
  3. Oxygen saturation ≤ 92% on pulse oximetry (breathing air). Absence of cyanosis is a poor discriminator for severe illness.
  4. Respiratory exhaustion:
     • Adult: new abnormal breathing pattern, e.g. alternating fast and slow rate or long pauses between breaths.
     • Child: respiratory exhaustion or apnoeic episode - apnoea defined as a ≥ 20 second pause in breathing.
  5. Evidence of severe clinical dehydration or clinical shock:
     • Adult: systolic blood pressure < 90 mmHg and/or diastolic blood pressure < 60 mmHg. Sternal capillary refill time > 2 seconds, reduced skin turgor.
     • Child: evidence of severe clinical dehydration or clinical shock. Sternal capillary refill time > 2 seconds, reduced skin turgor, sunken eyes or fontanelle.
  6. Altered conscious level:
     • Adult: new confusion, striking agitation or seizures.
     • Child: strikingly agitated or irritable, seizures, or floppy infant.
  7. Causing other clinical concern to their own GP or clinical team: e.g. a rapidly progressive or an unusually prolonged illness.

Inform local Flu Response Centre⁷ by phone, e-mail or fax to ensure access to antiviral treatment.

Antiviral treatment⁸

Testing has shown that the human swine influenza A/H1N1v can be treated with the antiviral oseltamavir (Tamiflu®) and zanamivir (Relenza®).⁹ Standard treatment dose of oseltamivir in adults (age > 13 years old) is 75 mg bd for 5 days. Paediatric suspension of oseltamavir is available (see SPC for dosages),¹⁰ and the hard capsules can be opened and contents sprinkled on food when suspension is not available (see SPC).¹¹

Standard treatment dose of zanamivir is 10 mg bd for 5 days (inhaled),¹² and may be more suitable for pregnant patients and those with renal failure.¹³

Prophylaxis should not ordinarily be given to contacts. However, clinical judgement should be used where risk is identified to particularly vulnerable individuals. In particular, prophylaxis may be considered in the following circumstances:¹⁴

• Prophylaxis in household settings - where there is close prolonged contact in a household setting by someone belonging to a higher risk group;
• Prophylaxis in institutional settings - where people at high risk of the complications of influenza live in close proximity. The decision to provide prophylaxis for control of disease in an institutional setting should be made on a case-by-case basis and should usually be made by the local health protection unit.

As described in Influenza record.