THREE patients have died in Scotland after catching a new strain of hospital bug Clostridium difficile (C.diff) – the first cases of their kind in the world.

All three were treated in the same health board area and two were in one hospital at the same time.

Health Protection Scotland (HPS), which is responsible for monitoring healthcare infections, is refusing to name the health board concerned.

The patients, who were all seriously ill with other conditions, contracted C.diff ribotype 332. HPS says it is the first time people falling ill with this rare form of the bacteria has been reported anywhere in the world.

An investigation has been launched to discover how the bug might have spread from the first two patients, who were diagnosed with the infection in December and January, to the third patient.

The individual was treated in a different hospital 15 miles away in March. C.diff was a contributing factor in the third patient's death.

Samples from other patients who may have crossed the paths of both parties are being checked for the new C.diff bug.

Dr Camilla Wiuff, strategic lead for microbiology at HPS, said: "We know the three patients themselves were not moved or transferred because they were too ill from other conditions, but it is difficult to completely eliminate that other patients have not been transferred or gone through the same admissions unit at some point."

It is understood a separate review has been ordered by the health board concerned to see whether mistakes in the care of the patients led to the infections.

The DNA of C.diff continually evolves in the bacteria's fight for survival, resulting in hundreds of strains or ribotypes. Last year a new strain, known as ribotype 244 – which has been linked to a sudden increase in cases and more severe illness in Australia – was also found in Scotland. Dr Wiuff said of ribotype 332: "It might not develop any further, it might stay as a rare ribotype. It has caught our attention because there has been these three cases in a very small geographical area. That is why we are alerting our NHS colleagues in hospitals."

Patients become vulnerable to C.diff infections when antibiotics they have taken for other health problems destroy the so-called "good" flora in their gut, giving C.diff the chance to multiply. Rates of the illness among hospital patients in Scotland have fallen dramatically since 2009 amid a crackdown on hygiene and antibiotic prescribing. In 2011 C.diff caused or contributed to 169 deaths in Scotland, compared to 270 in 2010 and 465 in 2009.

Dr Wiuff said such infection control measures had been very effective against the most common types of C.diff but scientists were now seeing a more diverse range of strains which may require more complicated treatment. She added: "In terms of the number of cases, we might get a flatline now where we cannot get the reduction down before we find out where these new strains come from."

Professor Hugh Pennington, emeritus professor of microbiology at Aberdeen University, said it was not known why new strains evolve. He added: "We can watch these bugs coming and going and sometimes they might get nastier, but the bottom line is, it is the same control measures which need to be in place for all ribotypes."

A Scottish Government spokesman said: "HPS has active surveillance and infection control measures in place. Research shows that, although this is a new strain, there is no increased risk to patients or the public.

"Healthcare-associated infections have reduced significantly over recent years, however, this remains a key priority. Staff, patients and visitors all have a role to play in making sure good standards of cleanliness and hand hygiene are maintained."