An E coli infection linked to the death of a doctor in Princess Margaret Hospital is unlikely to lead to widespread transmission, according to renowned microbiologist Yuen Kwok-yung.

He said on Wednesday the infection might have spread through the shared restrooms in the offices of three doctors in the hospital, although he did not rule out other possibilities.

The infection of the Shiga toxin-producing Escherichia coli involved three oncologists at the hospital, all of whom had gastrointestinal symptoms, such as diarrhea, in the past week. One of them – a doctor in his 30s – died on Feb 7 despite being treated with antibiotics.

Speaking in a radio program, Yuen, who heads the infectious disease unit at the University of Hong Kong’s Department of Microbiology and is helping in investigations into the cause of the infection, said since Shiga toxin isn’t airborne and healthcare professionals have adhered to hand hygiene practices before interacting with patients, it’s unlikely there would be widespread infections within the hospital, and subsequent transmission to patients is minimal.

He said the avenues of infection for Shiga toxin-producing bacteria typically involve food and water contamination.

These pathogens are commonly present in raw beef, unpasteurized milk, and similar products. He said residents should eat fully-cooked food, warning that undercooked beef and salad with sprouts are high-risk foods.

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Yuen said if the cluster infection had spread in restaurants, it would be likely more than three doctors would have been infected.

He believes the shared restrooms within the offices of the three infected doctors might have been the transmission route. Toilets are communal and often moist, which might help the spread of the disease.

Environmental samples of the doctors’ office and the shared restroom have been collected for further tests and investigations, hoping to identify the source of the infections.

Yuen noted there’re many uncertainties in the case, and it may take a long time before a conclusion is reached. At this stage, other potential causes of death, such as chemical-related issues or autoimmune problems, cannot be ruled out. He said the latest gene sequencing technology is being used for further investigation.

The stool sample of one of the doctors with mild symptoms had tested positive for the Shiga toxin-producing E. coli, while those for the other two, including the deceased, proved negative.

It’s possible that the two patients who didn't test positive had taken antibiotics before providing their stool samples, and this could have interfered with the detection of the virus, Yuen said.

He warned that once a person is infected with the Shiga toxin, taking antibiotics might worsen the patient’s condition, and complications might follow. Medical workers with diarrhea should avoid taking antibiotics directly, and should examine their stool first to help in the diagnosis.

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Shiga toxin-producing E. coli infections are considered rare in Hong Kong, with an average of zero to six reported cases annually. The Center for Health Protection received five reports of infections last year and six in 2023.