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Last Updated: Friday, 4 November 2005, 17:44 GMT
How the virus might spread

Angela McLean
The way people behave has a profound effect on how fast an epidemic spreads through a community
Angela McLean
Angela McLean is Professor of Mathematical Biology in the Department of Zoology and Director of the Institute for Emergent Infections of Humans in the James Martin 21st Century School.

She uses mathematical models to aid our understanding of the evolution and spread of infectious agents. This encompasses modelling of the dynamics of infections and immune responses within individual hosts as well as models of the spread of infections from one host to another.

The way people behave has a profound effect on how fast an epidemic spreads through a community. This is because of the direct link between human behaviour and transmission of infection from one person to the next.

This was clearly illustrated during the SARS epidemic where the time from onset of symptoms to hospitalisation in Hong Kong fell from seven days at the start of the epidemic to just two days a month later.

Isolation of cases through hospitalisation was enough to end the SARS epidemic. This was only true because SARS patients were not very infectious during the early days of their illness.

Unfortunately people tend to be very infectious with influenza even before they feel ill and for this reason it is unlikely that isolation of influenza cases would be sufficient to stop an influenza pandemic.

Even if isolation of cases could not stop a pandemic it could play an important role in slowing the spread of infection so that the epidemic curve is longer and flatter.

This would mean that the weeks with the highest number of very sick people were less likely to overwhelm hospital services.

Staying at home once sick is an important way for people to avoid infecting others, but there are other behaviour modifications that can make individuals less likely to become infected in the first place.

Avoiding large gatherings and frequent hand-washing are two ways to reduce the risk of catching influenza. The first simply reduces the risk of encountering someone who is infectious. The second reduces the risk of transferring infectious viruses that are on the hands into the eyes or mouth.

There is a range of evidence showing that viruses that cause colds and flu pass rather easily from hand-to-hand and that people who wash their hands frequently are less likely to catch these respiratory diseases.

Of course this is a behaviour modification that will protect against colds and influenza any winter - not only during a pandemic.


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