Authorities in Thailand say they are still not certain what caused the death of six tourists in the northern city of Chiang Mai but suggest some may have died from being exposed to pesticide or other toxic chemicals.
The deaths include that of a Thai tourist guide, two tourists from Britain, one tourist from France, one tourist from New Zealand and one from the United States. The tourists were staying in three different hotels in the city during January and February 2011. Three other tourists also fell ill but recovered.
The latest news comes from a posting on the Thai government's Department of Disease Control website on Tuesday, that said the authorities have have conducted an investigation into the mysterious deaths but the results were inconclusive, and the "specific agents that caused the deaths and illnesses in these events cannot be identified". It also says the authorities cannot establish exactly how the victims came to be exposed to them.
The American tourist who died was a 33-year-old woman. She died on 11 January from injury to the heart muscle. The website report suggests here death was probably caused by a "chemical or biotoxin" pesticide and that lab tests ruled out drugs and viral causes. Her travelling companion, a 29-year-old woman from Canada, also got sick but recovered. Both were staying in the same hotel room at one of the three hotels.
A 25-year-old French woman died 19 January. In her case, the investigation concluded her death was unrelated to the others. They found she had died of severe myocarditis (inflammation of all the heart muscles), most likely due to a viral infection rather than exposure to a poison. She had checked into a second of the three hotels, and a female travelling companion who checked in at the same time did not get sick.
Most of the evidence so far concerns four women: a 47-year-old from Thailand, who was found dead on 3 February, a 23-year- old from New Zealand, who died on 6 February and her two friends, also 23 years old, who recovered.
The three New Zealand women fell ill on 3 February and were found to have developed severe metabolic acidosis (abnormal acid level in circulation) and two of them had injury to the heart muscle. The Thai woman probably died from sudden arrhythmia, said the report. All four women were staying in the same hotel, the third of three investigated.
The investigators suggest the cause of the sickness in the four women was probably the same, given the proximity of their rooms, and it is unlikely to be bacterial or viral and may be "some toxic chemical, pesticides or gas". They ruled out pesticides in the "organophosphate, organochlorine and carbamate group, such as cholpyrifos, are also unlikely to be the cause because they conflict with clinical specimens and blood test".
Tests also ruled out other chemicals, such as "sodium monofluoroacetate (compound 1080) and phosphine gas", but the report also emphasizes that negative results do not always confirm absence, as chemicals can dissipate before the tests are done. The investigators also found aluminium traces in some of the rooms and elsewhere in the hotel, but no evidence it came from the pesticide aluminum phosphide.
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