A suspected E. coli outbreak at Princess Margaret Hospital that is thought to have claimed the life of a doctor and sickened two others could have spread in a washroom, a microbiologist said on Wednesday.

Hong Kong University's Yuen Kwok-yung told RTHK that this is because the bacteria survive longer in humid conditions.

"Because they would use the same toilet in their department and that of course could be a place of transmission," he said.

"After using the toilet it would be humid, therefore it is possible that the virus was spread there."

Yuen added, however, that since the washroom in question would have been sanitised before samples were taken, the likelihood of finding E.coli there is slim.

Three oncologists at the hospital are thought to have caught E. coli. While one died last Friday, the other two only had mild symptoms.

Yuen said the deceased oncologist was young and was not known to have been suffering from chronic illnesses, so work was still ongoing to find out why the doctor may have succumbed to such an infection.