H1N1 is a relatively recent strain of the influenza virus, known as swine flu. It was first identified in Mexico in April 2009, and declared a global pandemic in 2009/10. The epidemic was not as serious as feared in the UK, with most cases being relatively mild. However, some people became more seriously ill and some died, including previously healthy people. It spread quickly because it was a new type of flu virus that few, if any, people had full resistance to. It is also possible that the virus will change over time and become stronger.

Although it is no longer considered a pandemic, H1N1 was still the main flu virus circulating during the UK's 2010/11 winter flu season. Some people were seriously ill and there were some deaths.

H1N1 is very contagious and spreads from one person to another in small droplets of saliva when someone with swine flu coughs or sneezes – the same way colds and ordinary flu are spread. The virus can live on a hard surface for 24 hours and on a soft one for about 20 minutes. People can be infected through the droplets left by an infected person on objects such as phones, keyboards and door handles.

The incubation period is usually between two and five days but can be up to seven in children. People are most infectious soon after they develop symptoms and are not considered infectious anymore once their symptoms have disappeared.

Good hygiene is the most effective way of stopping the transmission of viruses such as H1N1. Washing your hands regularly with soap and water and cleaning surfaces regularly will help prevent infection. For people with H1N1 flu, sneezing and coughing into a tissue, throwing the tissue away and then washing your hands, will also help prevent onward transmission.

Swine flu can be treated with the antiviral medicines oseltamavir and zanamivir. In some situations, people with HIV may be entitled to receive one of these as a preventive measure.

If you do have a low CD4 count or have an AIDS-defining illness, it would be a good idea to check with your HIV clinic whether you could be taking any other action to reduce risk.

A vaccine was developed against the H1N1 virus and, as was the case last year, in 2011/12 it is being included in the seasonal flu vaccine. This means a seasonal flu vaccination will protect you against H1N1 and other strains of flu.

It is recommended that people in high-risk groups, including people with HIV, be vaccinated. People with HIV are entitled to receive the vaccination free of charge. The vaccine is available at GP surgeries. You will need to be registered with a GP and to have told them of your HIV status.

Research has shown that the vaccine is safe in people with HIV; like other seasonal flu vaccines, it doesn’t have ‘live’ virus in it. The vaccine is effective in people with HIV, although there is some evidence that people with low CD4 counts are less likely to be protected by it. One study found that a booster dose improved the number of people with HIV protected by the vaccine.

Your GP should take into account other drugs you are taking that may interact with the flu vaccine. You can check for any reported interactions between the flu vaccine and anti-HIV drugs at www.hiv-druginteractions.org.

HIV-positive people do not seem to be at higher risk of getting swine flu.

Some people are considered at higher risk of complications if they get H1N1, including people whose immune systems are damaged. Some research has shown that generally HIV doesn't seem to affect the severity or outcome of having swine flu, although having a low CD4 cell count (under 200) can increase the risk of complications. Having a condition such as asthma or TB as well can increase the risk further, especially as complications are most often chest infections such as bronchitis or pneumonia. 

The symptoms of swine flu are similar to the symptoms of regular seasonal flu. People usually have a fever or high temperature (over 38°C or 100.4°F) and two or more of the following symptoms: unusual tiredness; headache; runny nose; sore throat; shortness of breath or cough; loss of appetite; aching muscles; diarrhoea or vomiting.

It’s possible that, if the numbers of people with swine flu go up dramatically at any stage, services at HIV clinics may be disrupted – or that you will be advised not to come in because of the risk of becoming infected yourself. Or you may be unwell and be unable to attend an appointment.

If you are on treatment, you should make sure you have enough supplies of your anti-HIV drugs to see you through – at least one month’s supply at any time. You could talk to your clinic about extra supplies at your next appointment.

Generally , you should stay at home, rest, drink plenty of fluids, and use over-the-counter painkillers to relieve symptoms. Contact your GP for advice.

Swine flu can be treated with the antiviral medicines oseltamavir (Tamiflu) and zanamivir (Relenza). The drugs must be taken at or near the start of the illness to be effective. They are not a cure, but can relieve symptoms, shorten the length of time you are ill and reduce the risk of complications.

You should contact your GP if you have symptoms of swine flu and you have a serious existing illness (not including HIV if you have a CD4 count of over 200 and are otherwise well) or you are pregnant. Similarly, contact your GP if a child under twelve months shows symptoms of swine flu.

You should also contact your GP or go to A&E if you have swine flu and:

• your condition suddenly gets much worse. Things to look out for include shortness of breath or difficulty breathing; turning blue; chest pain; bloody or coloured sputum; being unusually drowsy or confused; a high fever lasting more than three days; low blood pressure. In children, you should watch out for fast or laboured breathing; lack of alertness; difficulty in waking up and little or no desire to play.
• after seven days (five for a child) your condition is still getting worse or fails to respond to antiviral drugs.

There is more information on swine flu on the NHS Choices website.

We will be reporting on any new information on swine flu and HIV as it becomes available on aidsmap. Sign up to our email bulletins to be kept informed of new developments.