New strains of a superbug are spreading among healthy people in the community, doctors have warned.
New strains of MRSA have been identified
The MRSA or methicillin-resistant Staphylococcus aureus is a recognised problem in hospitals and nursing homes, where it spreads between patients weakened by illness.
Now different strains are spreading among healthy people in the communities.
Outbreaks have been seen in the US and Europe, including cases in Scotland.
These strains are spread via skin-to-skin contact and appear as sores which look like insect bites.
Although these bugs can be very unpleasant, they are not life-threatening in themselves
Dr Giles Edwards, Scottish MRSA Reference Laboratory
If not treated properly, abscesses and boils can develop.
It is not certain if each outbreak is caused by exactly the same strain, but most appear to contain a gene called PVL, responsible for the production of a toxic protein.
Doctors believe it is this gene which causes the spread of the MRSA strains between healthy people with unbroken skin who would not normally be expected to pick up infections in this way.
New Scientist magazine reports outbreaks have been seen in US prisons, towns and cities.
Athletes, schoolchildren and newborn babies have been infected.
Many cases have also been seen amongst the gay community.
MRSA is not spread through sexual contact, but doctors say the more partners a person has, the higher their risk of contracting the superbug.
Cases of PVL strains have also been seen in the Netherlands, Scotland and France.
The strains are resistant to methicillin, but do respond to several common types of antibiotic.
Dr Giles Edwards, deputy director of the Scottish MRSA Reference Laboratory, which identified two strains of PVL strains, told BBC News Online: "Although these bugs can be very unpleasant, they are not life-threatening in themselves.
"But it's known that these PVL strains are associated with the much rarer condition of necrotising pneumonia. That's certainly a life-threatening infection."
In the US, health experts are concerned about the spread of community MRSA infections.
Elizabeth Bancroft, of the Los Angeles County Health Department, said hospitals have reported "scores" of cases amongst gay men in the city.
Thirty-five children have also been admitted to hospital with the infection.
In the county jail, almost 1,000 prisoners have been affected, with 66 needing hospital treatment.
Other cities including New York, Boston and Miami have also seen outbreaks.
In San Francisco, health officials have sent an MRSA alert to masseurs, gyms and sex club operators.
Diane Portnoi, chief investigator at the San Francisco Health Department, said: "We're monitoring the situation very closely.
"Most likely there have been some deaths due to these cases. But we don't know for sure because we just don't record MRSA deaths."
Scott Fridkin, a medical epidemiologist at the US Centers for Disease Control in Atlanta, Georgia, which is investigating the outbreaks, said: "We are greatly concerned that MRSA has emerged in the community in people with no ties to healthcare."
Health officials are running checks to see if all the cases in Europe and the US have been caused by the same strain.
US health officials have confirmed the LA cases are all from the same strain of MRSA, which was first isolated in New York in 1997.
Dr Edwards said it was likely that the US strain would spread to Europe, if it had not already done so.