The infection came to light after a whistleblower contacted the Scotsman to say all elective surgery, which is necessary but not emergency, had been suspended on Monday and Tuesday.
A multidisciplinary Incident Management Team (IMT) has been deployed but the original source of the infection has still to be identified.
The number of patients affected is believed to be under five and they are being monitored in the hope that their condition does not deteriorate.
NHS Lothian confirmed the patients are suffering from different strains of the bacteria Pseudomonas aeruginos, found widely in the environment, including in soil and ground water.
This bacteria thrives in wet places such as sinks, drains, taps and showers. Infections caused by P.aeruginosa can normally be treated with antibiotics.
READ MORE: Glasgow hospital baby deaths source may ‘never be known’, admits health chief The latest infection comes after a spate of incidents in the NHS Greater Glasgow and Clyde health board including the death of two babies who contracted the staphylococcus aureus bacterium at the Princess Royal Maternity Hospital in January.
READ MORE: Health Secretary rejects claims half of Scots hospitals haven’t had safety inspection Professor Alex McMahon, Director of Nursing, NHS Lothian, said: “A very small number of patients in a ward in the Western General Hospital, Edinburgh, have been identified with an infection caused by the bacteria Pseudomonas aeruginos. The cases, which are not linked, continue to be treated and the patients are being monitored very closely.
“A multidisciplinary Incident Management Team (IMT) has been established and tests are ongoing.
“The bacteria has been identified in a shower and some taps in one area of a ward in the Department of Clinical Neurosciences. This bacteria is common and rarely affects healthy individuals, but can be harmful to a small number of patients who are very vulnerable to infection.
“All necessary infection control measures are being carried out in the ward and, as a precaution, also in an adjacent area, to ensure patient safety is maintained.
“Unfortunately this has resulted in elective procedures in the department being postponed on Monday and Tuesday.
"We are sincerely sorry for the inconvenience and disappointment this inevitably causes our patients and their families however, above all else, we must prioritise the safety of our patients."
In December a 10-year-old boy and an adult died after becoming infected with cryptococcus, an infection related to pigeon droppings at the Queen Elizabeth University Hospital in Glasgow.
Miles Briggs MSP, Shadow Cabinet Secretary for Health said: “It is deeply concerning to learn that patients in a ward at the Western General Hospital, have been identified with an infection caused by the bacteria Pseudomonas aeruginos. I sincerely hope those patients infected make a quick and full recovery.
“It is obviously crucial that all infection control procedures are followed and that the infection is contained as quickly as possible.
“Patients and staff will no doubt be extremely concerned at this latest outbreak at a Scottish hospital and they must be reassured that the hospital is safe
“It is now crucial that NHS Lothian and the SNP government are as open and transparent as possible, to ensure these incidents do not reoccur.
Labour health spokeswoman, Monica Lennon MSP added: “The news of another potentially serious infection outbreak in a Scottish hospital will worry people right across the country, at a time when the Health Secretary recognises that confidence has been shaken.”
“Our hospitals and health centres should be places where people go to get better, not run the risk of falling ill through infections.
“The Health Secretary must keep patients in the Lothians and Parliament updated on this latest outbreak.”