A second person in the UK has caught swine flu without having visited Mexico, tests have confirmed.
The news follows the case of Graeme Pacitti from Falkirk, who was infected after contact with the first Britons to develop the flu, Iain and Dawn Askham.
The UK's second "onward transmission" case is thought to be a 42-year-old man from South Gloucestershire.
Meanwhile, a new case of swine flu has been announced in South-East England, bringing the UK total to 13.
Director of Public Health for South-West England Dr Gabriel Scally said the Gloucestershire patient had not been taken to hospital.
"The man himself is as well as can be expected and he has been very effectively and very rapidly treated. Like many of the other cases in the UK, it has been a relatively mild illness for him," he told the BBC.
Symptoms of swine flu in humans appear to be similar to those produced by standard, seasonal flu.
Cases 'not connected'
In cases outside Mexico - where the virus is suspected in more than 160 deaths - the effects do not appear to be severe, although the death of a Mexican child has been confirmed in the US.
The World Health Organization has set its pandemic alert level at five but says it has no immediate plans to move to the highest level of six.
Earlier the Health Protection Agency confirmed that a woman from the Merseyside area and a schoolgirl in South-West England had contracted the virus.
Both had recently returned from Mexico.
The girl's school - Downend, which is also in South Gloucestershire - will be closed until 11 May and parents have been told to contact their family doctor if any child shows symptoms.
Officials said the two Gloucestershire cases were not connected.
"It is concerning but I have to stress that it doesn't mean there's more reason for people to worry," she said.
"We are still very much in the containment phase of this infection."
Of the 13 UK cases confirmed so far, all are thought to have responded well to treatment.
Prime Minster Gordon Brown, who was visiting an NHS Direct centre in Beckenham, south-east London, said the UK was in a good position to cope with the illness .
"There will be more cases, but at the same time it is treatable," he said.
"If we can get to people quickly, we can trace their contacts and if we can give those affected Tamiflu [anti-viral drug], then we can avoid the problems that we see in some of the other countries," he said.
England's Chief Medical Officer Sir Liam Donaldson has said it is impossible to predict how many deaths there could be in the UK until more is known about the virus strain.
Members of the public can call 0800 1513513 for recorded information about swine flu. In Scotland, anyone with concerns about the virus can call 08454 24 24 24.
An advertising campaign urges people to catch the sneeze before binning the tissue
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