Mystery remains after pesticides blamed for Thailand tourist deaths

The father of one of the tourists has called for a fresh investigation into her death after Thai authorities said she had probably died after eating 'toxic seaweed'

Questions remain over the mysterious deaths of six foreign tourists and a local tour guide in the northern Thai city of Chiang Mai despite a five-month investigation.

The deaths, including those of an elderly British couple and a 23-year-old New Zealand backpacker, occurred between January and March this year. Four of the victims died while, or shortly after, staying at the same hotel and all but one died from sudden heart failure.

The report from Thailand's Department for Disease Control said three of the victims "probably died of exposure to pesticides" but it is not known what the chemicals were. The agency's report concluded that George and Eileen Everitt, from Boston, Lincolnshire, could have been poisoned by the same chemicals, but a direct link to the other deaths could not be found.

"Despite the best efforts of the Thai authorities and their international partners in undertaking an exhaustive investigation [...] the precise causes for the deaths and illnesses cannot be definitively identified or confirmed," the report concluded. Full laboratory tests had been inhibited due to inadequate samples, because the need for such tests was "not foreseen at the time of death", it added.

Mr and Mrs Everitt's son Stephen said he was frustrated by the investigations' conclusions. "The case may be closed to the Thai authorities, but not to me," he told The Independent. Mr and Mrs Everitt were found dead in their room at the three-star Downtown Inn hotel in Chiang Mai on 19 February. Thai authorities said the couple suffered fatal heart attacks just minutes apart.

"I don't understand why such deadly chemicals would have been used in a hotel – there's no explanation. The Downtown Inn is still open and no one has been held accountable for what happened. We need answers," Mr Everitt said. David Mabey, professor of communicable diseases at the London School of Hygiene and Tropical Medicine, said it is "very surprising" that such strong pesticides should be used in a hotel, but said little more can be done to investigate the deaths without adequate samples to work from.

Thailand's public health department enlisted experts from the World Health Organisation in May after doubts were raised over claims made by local authorities that the deaths were coincidental, and possibly caused by food poisoning.

Richard Carter, father of the New Zealand backpacker Sarah, called for a fresh investigation into his daughter's death after Thai authorities said she had probably died from myocarditis (swelling of the heart) after eating "toxic seaweed" from a market next to the hotel.

A Thai tour guide who had been staying in a room next to Ms Carter and the Everitts died on 3 February, three days before Ms Carter.

The report said Thai authorities are "taking measures to reduce the risk of chemical and pesticide exposure to future visitors to Chiang Mai and other main tourist provinces".