The flu: what are the symptoms and what should I do?

The flu has arrived, folks. With latest figures showing a doubling in the rates of ILI (influenza-like illness) in the community, it’s time to batten down the hatches in advance of what some experts have said will be an especially bad flu season.

Predictions of so-called “Aussie flu” – a H3N2 strain of influenza A that caused a nasty epidemic in the southern hemisphere winter just gone – have been proved correct. But what is a surprise is the emergence of equivalent numbers of the completely separate influenza B virus. Usually just one type, either influenza A or B, is responsible for the majority of cases.

The term influenza originated in the Italian Renaissance when an outbreak of flu was thought to be due to the influence of a particular planetary alignment. There are three types of flu virus: influenza A, B and C, and within each type lies the potential for a myriad of subtypes.

All viruses are able to mutate. They alter their genetic make-up in response to changing environmental circumstances. Influenza virus is especially good at this, which explains why you can catch flu more than once and also why it is necessary to vaccinate people annually.

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Flu virus invades the cells of the human body by injecting a spike of its own cell wall into the cells of the respiratory tract. It then begins to multiply, using the human cell as a new home.

The virus reaches the respiratory tract via droplets in the air, which come from the coughs and sneezes of other flu victims.

The H and N nomenclature used to identify particular sub types of Influenza A refers to proteins on the surface of the virus. One is called neuraminidase (N) and it enables the replicating influenza virus to break away from the cell it initially invaded and to spread throughout the body.

There are nine types of neuraminidase. The other is haemagglutinin (H), of which there are 12 basic types; it is the means by which the virus enters the cells of its host.

Antiviral drugs such as Tamiflu act as neuraminidase inhibitors and prevent newly formed influenza particles from escaping infected cells, thereby interrupting the spread of infection within the body.

Infection rates are not yet at flu epidemic levels and there is certainly no evidence that we are in for a season equivalent to the 1968 Hong Kong influenza pandemic experience, despite the doomsday predictions of some. That flu pandemic cost an estimated one million lives across Asia, Europe and the US.

A recent study in The Lancet provided a much needed update on the global mortality burden of seasonal influenza. The authors calculated a new estimate of 291,243–645,832 seasonal influenza-associated respiratory deaths per year (4–8·8 per 100,000 people). This is an increase on previous figures; in addition older people were shown to have high mortality at 51·3–99·4 annual deaths per 100,000 individuals for those aged 75 and older.

What should you do if you think you have the flu?

The sudden onset of symptoms such as fever, cough, sore throat, aching muscles and joints mean you should probably isolate yourself in bed. Drink plenty of fluids and take paracetamol to reduce your temperature. Most people will recover with self-care in about a week to 10 days after the onset of infection.

However, if you develop any of the following, then it is important to seek medical advice: increasing difficulty breathing, for example unable to complete a sentence; sharp chest pains that make it difficult to breathe or cough; thick yellow or green phlegm or bloody phlegm; severe ear ache; uncharacteristic changes in behaviour such as becoming confused or appearing terrified (particularly in children); and being so drowsy as to have difficulty eating, drinking or talking.

And finally: man flu and woman flu are treated similarly.