A combination of food poisoning and asthma likely caused the deaths of a Queensland mother and daughter who died in Bali.

The chances of Noelene and Yvana Bischoff dying from a rare form of food poisoning were one in a million, maybe a billion.

Had the Queensland mother and daughter been served a different piece of fish when they sat down for dinner at the Padang Bai Beach Resort in Bali last month they may still be alive.

And had anyone else been served the same meal, it’s unlikely their symptoms would have been fatal.

“This is just a one in a million – one in a billion – thing to happen,” Noelene’s brother Malcolm Bischoff told Fairfax Media.

He says autopsies have shown the pair likely died from scombroid (histamine) poisoning, a rare form of food poisoning that’s extremely unlikely to cause serious illness.

It’s caused by elevated levels of histamine being present in fish, which can cause an allergic reaction.

Noelene and Yvana were asthmatic and it’s believed this may have contributed to their severe reaction.

Mr Bischoff said the pair was extremely unlucky.

“It is also possible that other people ate pieces of the fish further away from (the contaminated part of the fish) that may have been fine,” he told ABC Radio.

The pair became violently ill less than a day after checking in at the Padang Bai resort.

Noelene, a 54-year-old nurse, died on January 4 while being taken by ambulance to a hospital in Denpasar. Yvana, 14, died hours later at the clinic without knowing her mother was dead.

Australian Medical Association federal president Steve Hambleton said the pair’s asthma put them at greater risk.

“From what we’ve read they got a pretty big dose of the histamine which resulted in all of those symptoms; the palpitations, burning, headaches, anxiety, the diarrhoea and abdominal pain,” he told AAP.

“Plus they had asthma so they got the respiratory symptoms and those in combination is probably where it went wrong.”

He said it was unlikely the pair would have survived had they been treated in Australia.

“From the severity of their attack it may have been that no matter where they were they wouldn’t have been able to be rescued,” he said.

Scombroid poisoning is rare and severe cases are almost unheard of.

OzFoodNet figures show 57 people contracted the poisoning in Australia between January 2009 and December 2013. Nine were hospitalised but no deaths were reported.

Symptoms include welts or a chest rash, and relief is provided by common anti-histamines.

Dr Hambleton says Noeline and Yvana would not have been able to detect high levels of histamine in the fish as it doesn’t alter the taste.

“You can’t taste, it could be a delicious reef fish that tastes pretty good,” he said.

He says the handling of fish immediately after it has been caught was a critical factor, and the disease could arise if it was improperly cooled or left to thaw for too long.

Although the disease is rare, Dr Hambleton advised travellers to stick to well established tourist spots when eating out overseas, rather than roadside stalls.