Influenza

Dr Matt Doyle gives a round-up of the latest thinking on another key nMRCGP subject area

What is it?

RNA viruses of the family orthomyxoviridae with serotypes of A,B and C. Influenza A is further categorised by its surface antigens: haemagglutinin and neuraminidase, hence nomenclature such as H5N1. Causes a respiratory illness responsible for significant morbidity and mortality worldwide. Primary transmission route is aerosol (such as coughing and sneezing).

Average incubation period two to three days. Period of infectivity can range from less than a week to several weeks in immunocompromised individuals.

Is it a problem?

It certainly was in 1918/19 during the Spanish Flu pandemic. Estimates suggest up to 100 million people lost their lives throughout the world. This was the H1N1 virus and it predominantly affected young and healthy people.

The Asian Flu outbreak (H2N2) in China between 1957 and 1958 was responsible for more than a million deaths. Hong Kong Flu (H3N2) caused more than one million deaths in 1968/9. Avian Flu (H5N1) is currently considered as a major pandemic threat. It has killed around 200 people worldwide (about 60 per cent of all confirmed cases).Each year up to 15 per cent of the population may be affected (primarily during the winter months).

Clinical

Can cause a broad spectrum of illness ranging from mild respiratory symptoms to a multi-system illness. Generally causes pyrexia, myalgia, coryza, headache, cough and pharyngitis.

Diagnosis is generally made on clinical grounds. Investigations (such as nasopharyngeal swabs) are useful for surveillance purposes.

Telling the difference between influenza and influenza-type illness can be difficult. A positive answer to the four questions below increases the likelihood of influenza:

• Are influenza viruses known to be in the local area?
• Does the person have systemic and respiratory symptoms, particularly cough?
• Did the person experience a sudden onset of symptoms?
• Is temperature significantly raised?

Antivirals

Under NICE guidance, antivirals are licensed and indicated for treatment of influenza in the following circumstances:

• Influenza is known to be in the area
• The patient is able to start treatment within 48 hours of symptom onset
• They are in an at-risk category: over 65, diabetic, immunocompromised, severe cardiovascular, respiratory or renal disease

Oseltamivir (Tamiflu) is licensed from one year of age. It can also be used for prophylactic treatment.

Vaccination

Vaccination does not contain live virus; hence it does not cause influenza. Contraindicated in allergy to egg proteins. Offered under NHS to the following groups:

• Chronic respiratory disease or asthma needing continuous or repeated steroids or with exacerbations requiring admission
• Chronic heart, renal and liver disease
• Diabetics (excluding diet-controlled)
• Immunosuppressed patients, and over-65s

Current controversies

Supply

Difficulties in growing one of the strains for this season's flu vaccination UVIG (UK Vaccine Industry Group) announced in June 2006 resulted in delays in supplying all the 15.2 million vaccinations ordered by the Department of Health.

Value of vaccination programme

Dr Tom Jefferson of the Cochrane vaccine field in Rome argued recently that there was a significant gap between the evidence for the vaccination programme against influenza and the current policy for immunisation in the UK. Last year's vaccination programme cost the NHS £115m (BMJ 2006;333:912-915, 28 October).

Matt Doyle passed the MRCGP this year and works as a full-time partner in Huntingdonshire