A spicy rice snack pack very nearly turned into the last meal Richard Strang ate.

It left him in a four-day induced coma in Wellington Hospital, his stay due to a toxin not seen in New Zealand for more than 30 years.

Strang, who had been living in Japan, was visiting his mother in Wellington last month when he ate a pack of pre-cooked "heat and eat" organic risotto that was probably well past its best-before date.

He was struck down by botulism, a rare and potentially fatal illness caused by a toxin that attacks the nervous system.

His lungs and other organs began shutting down, and "it was all pretty much touch and go", he said.

The last - and only - suspected case was that of two Rotorua sisters thought to have contracted botulism from watercress and boiled mussels in 1984.

Botulism was also the toxin wrongly thought to have been present in a batch of whey sent to China by Fonterra in 2013.

Strang is still going through rehabilitation, and needs to stay in New Zealand until he regains enough strength to return to Japan.

The Ministry for Primary Industries said the rice snack he ate contained no preservatives, and "incorrect handling" was thought to be the cause of his illness.

The meal had been made following appropriate regulations, but MPI understood it was not refrigerated, as instructed, and was eaten "well after its likely best-before date".

Strang ate it despite noticing its "blue cheese" smell.

The ministry said that, as the manufacturer was not at fault, it was inappropriate to name the brand.

Regional Public Health medical officer of health Annette Nesdale confirmed Wellington Hospital's clinical diagnosis of botulism. "It's extremely unusual and rare. He is very fortunate to have had a good recovery."

According to the World Health Organisation, botulism comes from the bacterium clostridium botulinum, which produces toxins that are "one of the most lethal substances known".

The WHO estimates it kills 5 per cent to 10 per cent of those infected and warns: "Ready-to-eat foods in low-oxygen packaging are more frequently involved in botulism."

The American Medical Association reported botulism could be used as a biological weapon.

It poses "a major bio-weapon threat because of its extreme potency and lethality; its ease of production, transport, and misuse; and the need for prolonged intensive care among affected persons".

After eating the packet meal, Strang returned to his hotel in central Wellington. While having a bath that night he felt "terrible" waves of impending vomit. "They finally got so strong I had to stand up."

Strang then became violently ill. He called hotel reception and within a minute trained medical staff were in his room. He collapsed into their arms.

An ambulance crew rushed him to Wellington Hospital, where a doctor recognised his illness as possible botulism. He was in the intensive care unit in an induced coma for four days.

His lungs stopped working and he was put on dialysis. "My organs were shutting down."

Thanks to "absolutely brilliant and unrelenting" 24-hour care at the hospital, he came out of the coma and was taken to Kenepuru for rehabilitation.

During the ordeal, his weight dropped from 94 kilograms to 77kg.

Massey University food safety professor Steve Flint said botulism was incredibly rare in New Zealand but its spores could be found in many products. It was usually found in food that had been canned or preserved.

A more common form of food poisoning from rice was bacillus cereus, which usually came from rice that had been cooked then stored. Its main symptoms were vomiting and diarrhoea.

Laboratory confirmation of botulism was very difficult, especially in cases such as Strang's where the food in question had been disposed of, he said.