A lethal toxin suspected to be behind a fatal food poisoning outbreak at an eatery in Taipei was found in the stool of the restaurant’s chef.

Of the 34 people who took ill after dining at the Xinyi District branch of Malaysian restaurant chain Polam Kopitiam between March 18 and 24, two died, seven remain hospitalised and 25 are recuperating at home as at April 6, Focus Taiwan reported. Four are in critical condition.

The toxin, bongkrekic acid, was detected in faecal samples collected from the Xinyi outlet’s chef on March 27, said Deputy Health Minister Victor Wang in a Facebook post on April 6.

Earlier samples taken from his hands on March 24 also tested positive for the deadly toxin, which – even in a minute dose of 1mg – can kill a human being.

The same toxin was found in most of the sick diners, local media reported.

In his post, Mr Wang added that the chef’s health condition is normal. The chef underwent blood and urine tests for the toxin on April 5 but the results were negative, he added.

Mr Wang suggested that the chef might not have eaten the contaminated food but only ingested a trace amount of the acid, which his body then metabolised.

Mr Wang explained that the chef’s hands may have been contaminated when he touched tainted ingredients, and the toxin may have ended up in the stool sample he submitted for testing.

Mr Wang added that 14 environmental samples collected from surfaces in the chef’s home, such as door handles and a washbasin, on March 30 returned negative results for Burkholderia gladioli, a bacterium that produces bongkrekic acid.

To look for the bacterium is the “key to the incident”, he said. Health ministry inspectors collected 27 additional samples from two other places the chef visited on April 4 to test for the bacterium.

At present, contaminated flat rice noodles in char kway teow – a Malaysian favourite – are the primary source of the outbreak.

The two fatalities are a 39-year-old man who ate at the restaurant on March 22 and died two days later, and a 66-year-old man who ate there on March 19 and died on March 27.

All Polam Kopitiam outlets were ordered to close during the ongoing investigations, though Mr Wang’s post reiterated that the outbreak was confined to the Xinyi branch.

Although the restaurant passed a food safety inspection in 2022, Taipei health inspectors who visited the eatery after the outbreak found cockroach droppings on the premises, knives stored on the counter next to the sink, and a failure to provide employee health records, local media reported.

A special prosecutor is also overseeing the investigation, according to local media.