Authorities in Thailand trying to establish what caused five foreign tourists in the northern city of Chiang Mai to mysteriously die have said that there could be a link to exposure to toxic chemicals. A Thai tour guide also died. The government has said that a New Zealand woman and a Thai woman may have been exposed to gas, pesticides or a toxic chemical before they died.

Eileen and George Everitt, a British couple staying in the same hotel, also died and investigators are not ruling out a possible link. Toxic exposure may also have caused the death of an American woman, although she was staying in a different hotel.

The deaths occurred in January and February and it was reported at the time that other tourists had also fallen ill. Included in the report is the death of a French woman, although the authorities claim she was suffering from symptoms including a fever before she arrived in Chiang Mai and so have ruled that the case is likely to be unrelated.

The investigation into the deaths has been undertaken by the south-east Asian country’s Department of Disease Control in conjunction with the World Health Organisation. The report said it was not possible to identify the toxic agents which may have been a contributing factor.

However, an independent investigation by a TV station in New Zealand apparently found that there were traces of chlorpyrifos, an insecticide used to combat bedbugs, at the hotel in which the tourist from New Zealand had been staying.