Two Canadian sisters who were found dead in their Phi Phi Island hotel room in 2012 were probably killed by phosphine, a deadly chemical used to kill bedbugs, a Canadian coroner says.
Phosphine is officially banned in Thai hotels but is probably used illicitly for fumigation, Dr Renee Roussel was quoted as saying by the National Post newspaper in Toronto.
As many as 20 tourist deaths since 2009 throughout Southeast Asia, many of them in Thailand, may be linked to the chemical, she said.
Phosphine is one of few substances that can kill and leave little trace in the environment or in the body, according to the coroner's report.
The autopsies found lesions on the brain caused by a severe lack of oxygen, which is consistent with phosphine poisoning.
"Phosphine is a pesticide that kills all that lives and all that breathes," the report states, adding that the chemical is cheap and widely available.
"Science doesn't allow us to confirm [the cause of death] without a doubt. Maybe one day it will."
The Montreal-based coroner's conclusion, released last week, contradicts that of a Thai autopsy conducted in June 2012 on the bodies of Audrey and Noemi Belanger of Pohenegamook, Quebec. It identified the insect repellent DEET as the likely cause of death.
The Thai autopsies, conducted in Bangkok, suggested the sisters died after drinking a cocktail popular with the party crowd on the southern island. Served in plastic buckets, the drinks contain cough syrup, cola, DEET and the mild narcotic kratom.
Audrey, 20, and Noemi, 25, fell ill after their first night on Phi Phi on June 13, 2012 and were not seen again until a maid at the Phi Phi Palms Hotel found their lifeless bodies in their room two days later.
Dr Roussel said she found that the levels of DEET present in the victims' bloodstream were not toxic. Exhaustive toxicological analysis performed in Montreal also turned up no evidence that kratom had been consumed.
Laboratory testing done for more than 800 drugs, metals and chemicals found nothing except low levels of DEET, consistent with the amount that would be found on the skin of someone using the repellent, and an anti-malarial medication the sisters were taking.
The Canadian coroner reported that 20 western tourists, mostly women, have died in Southeast Asia in circumstances similar to the Belanger sisters since 2009, and phosphine is considered the likely cause. A Norwegian and an American died on Phi Phi in 2009.
The four Phi Phi deaths have similarities to a series of deaths in Chiang Mai, mostly at the Downtown Inn, a hotel that has since been demolished, and two deaths in Vietnam.
A British couple, a young New Zealander and a Thai tourist guide died in still largely unexplained circumstances in Chiang Mai.
Agents with the US Federal Bureau of Investigation, which has looked into unexplained deaths involving western tourists, travelled to Ottawa in 2013 to help with the Belanger investigation, and they also believed that phosphine was responsible, Dr Roussel said.
Her report calls on public health officials in Quebec to advise travellers of the lethal danger posed by some pesticides and to offer advice on how to detect symptoms of poisoning and treat it before it is too late.
For the women's parents, the new findings provided a small measure of comfort. For more than two years they have been living not only with the loss but also the suggestion that the women had been reckless.
"I am proud of my girls," father Carl Belanger told Radio-Canada after the coroner’s report was released. "If there had been the slightest hint of an overdose that Thailand could have pointed to, they would have. But they were not able to prove it. ... We knew our daughters were not drug users."