Scientists have identified an emerging "superbug" strain of salmonella that is highly resistant to the antibiotic Ciprofloxacin, or Cipro, often used for severe salmonella infections, and say they fear it may spread around the world.

The strain, known as S. Kentucky, has spread internationally with almost 500 cases found in France, Denmark, England and Wales in the period between 2002 and 2008, according a study in the Journal of Infectious Diseases.     

French researchers who led the study also looked at data from North America and said reports of infection in Canada and contamination of imported foods in the United States suggest the strain has also reached there.

The study was published on Wednesday as US health officials reported a multi-state outbreak of another strain of antibiotic-resistant salmonella -- called S. Heidelberg -- which has so far made 77 people sick and killed one.

Salmonella infection is a major public health problem worldwide. There are an estimated 1.7 million infections in North America each year and more than 1.6 million cases were reported between 1999 and 2008 in 27 European countries.    

Although most salmonella infections produce only mild gastroenteritis with stomach cramps, fever and diarrhoea, older people or those with weaker immune systems are particularly at risk of life-threatening infections.      

These cases are typically treated with drugs in a class of antibiotics known as fluoroquinolones, which includes the commonly-used medicine ciprofloxacin. Cipro was originally developed by Bayer and is now available as a generic.

But as with many bacteria, multi-drug-resistant, or "superbug", strains of salmonella infection have developed as the bacteria has found new ways of outfoxing the drugs, and these can spread in food and from person to person.

In the French-led study, Francois-Xavier Weill and Simon Le Hello from the Institut Pasteur looked at surveillance data from the European countries and the United States and found 489 reported cases of the superbug S.Kentucky strain. Case numbers rose every year from 3 cases in 2002 to 174 cases in 2008.     

They said the earliest infections seemed to have been picked up mainly in Egypt between 2002 and 2005, but since 2006 the infections have also been acquired in various parts of Africa and the Middle East.

"The absence of reported international travel in approximately 10 percent of the patients suggests that infections may have also occurred in Europe through consumption of contaminated imported foods or through secondary contaminations," they wrote. 

As part of the study, multi drug-resistant S Kentucky was also isolated from chickens and turkeys from Ethiopia, Morocco, and Nigeria, suggesting "poultry is an important agent for infection" the researchers said, adding the common use of fluoroquinolone antibiotics in chicken and turkey production in Nigeria and Morocco "may have contributed to this rapid spread".  -Reuters