Doctor: Even cooking mussels may not remove biotoxins

Doctors: Contaminated mussels from Australia can cause diarrhoea and vomiting
ZACHARY SOH The New Paper 24 Mar 16;

Squeezing lime juice on your shellfish may make it tastier, but don't count on it to kill the bacteria in your food.

Its acidity does not make your seafood any more hygienic to eat, said Dr Leong Hoe Nam, 45, an infectious diseases specialist at Mount Elizabeth Novena Hospital.

He was dispelling some myths about shellfish, following the recall of some batches of mussels from Australia.

The Food Standards Australia and New Zealand had warned that some batches of Spring Bay Australian mussels had been contaminated with a biotoxin which causes diarrhoeic shellfish poisoning.

Yesterday, The New Paper spoke to Dr Leong Hoe Nam and Dr Leong Choon Kit, 49, a general practitioner at Mission Medical Clinic, to better understand the dangers of consuming such shellfish.

Apart from the lime juice myth, another myth, said Dr Leong, the specialist, is that cooking the shellfish will make it safe.

He said: "Cooking may reduce some of the biotoxins in the shellfish, but not all of them, as some are heat stable. Even if you cook them a thousand times, it will not work.

"A biotoxin is a poisonous substance produced by a living organism. In this case, it is a toxin from the algae the mussels feed on.

"However, mussels in particular have more biotoxins than other kinds of shellfish as the toxins from the algae remain in them."

There is always a small amount of biotoxins in mussels, he added.

"A person (who eats them) will be fine as long as the amount does not cross his threshold," he said.

The contamination may be due to an increased amount of algae that produces more biotoxins.

"The mussels are at the mercy of the surrounding ecology," he said.

"The algae they eat may produce more biotoxins than other strains of algae. It is an uncontrolled situation with many environmental factors."

He added that these toxins can affect the intestines and even the central nervous system.

"In most cases, it can cause diarrhoea and vomiting, which leads to dehydration. In more severe cases, the toxins can affect the brain and lead to paralysis," he said.

"In extremely rare cases, it may even cause death."

He added that for mild cases, drinking water to replenish the fluids lost from diarrhoea and vomiting is essential.

However, for severe cases, one might need to be admitted to the hospital for intravenous rehydration for one or two days.

His advice? "Everything in moderation. If you are older or have a poorer immunity, eat less shellfish.

"The person who eats 20 mussels in one day may feel sicker than the person who just ate two."


Dr Leong, the GP, said most of the patients he sees for shellfish food poisoning are people who have just come back from overseas trips.

"They may have eaten seafood that was not freshly cooked. Some of them even have fever and blood in their stools."

He advised those who suspect they have shellfish toxin poisoning not to self-medicate, but to see their nearest GP.

"For most cases, it can be easily treated with proper hydration and antibiotics. But make sure to inform your doctor of any travel history."

The GP said that exercising universal precaution is important for frequent travellers.

He said: "I always tell my patients, 'When you are overseas, and your seafood is not freshly cooked in front of you, do not eat it.'"


The Agri-Food and Veterinary Authority (AVA) announced on Monday that selected batches of mussels from Australia have been recalled.

They had been contaminated with a biotoxin that may cause illness if consumed.

The affected products are the 1kg blue packets and 2kg yellow packets with use-by dates of March 24, 25, 26 and 27.

Also affected are the 1kg net bags with use-by dates of March 22, 23 and 25.

AVA advises those who have consumed the affected products to seek medical advice if they have concerns.