Results of the probe on Chiang Mai tourist and Thai guide deaths and illnesses completed

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Department of Disease Control, Thailand Ministry of Public Health

Update 5
Results of the probe on Chiang Mai tourist deaths and illnesses completed

16 August 2011

Thai authorities have concluded their investigation into the deaths of five tourists and a Thai guide. Following the months-long investigation, experts ultimately could identify the likely cause of death for most cases, but not the specific agents. Experts also concluded that some, but not all of the cases appear to have been causally related. The conclusions, investigation constraints, and actions taken by Thai authorities are explained in detail below.

The investigation covered the six deaths and associated illnesses of three other tourists (travelling companions) in Chiang Mai between 11 January and 19 February of this year. The conclusions follow an exhaustive probe during which Thai and international experts from numerous disciplines were consulted in several rounds of face-to-face, tele- and video-conferences to consider the available scientific evidence. These included clinical and biological samples from patients, the results of on site environmental experiments, and chemical samples from one of the concerned hotels and a nearby market. Chemical and tissue samples were tested at certified laboratories in Thailand, the United States, Japan and Germany during the course of the inquiry.

The investigation also included interviews with co-travelers and some family members in the US, Canada, France and New Zealand in an effort to gather information about all possible exposures. Potential viral, gaseous, toxin and chemical hypotheses were considered by domestic and international partners. These include the Department of Disease Control and the Department of Medical Sciences at the Ministry of Public Health; the Provincial Public Health Office, Chiang Mai; Ramathibodi Poisons Centre, Bangkok; the Ministry of Agriculture and Cooperatives; the World Health Organization (WHO), and the United States Centers for Disease Control (US CDC). Staff of the consulates and embassies concerned were also kept informed.

The final conclusions were reached by the official Chiang Mai investigation team in conjunction with a review panel of outside experts in infectious disease, toxicology, pathology and forensic medicine, epidemiology, and environmental science and pesticide use.

Investigation findings:
The people who died and fell ill were grouped under four events based on suspected causes. The case findings are as follow:

Event 1:
One American woman, age 33, died on 11 January. Her friend, a Canadian woman, age 29, fell ill but recovered. Both stayed in the same room at Hotel “A” and developed severe vomiting on the night of 8 January.

The diagnosis based on clinical and pathological findings is that the American woman died from myocardial injury (injury to the heart muscle). Laboratory tests indicate that drugs and other suspected viruses (Adenovirus, Echovirus, EBV, Influenza A) are unlikely to be the cause. The suspected agent that caused her death is likely to be chemical or biotoxin in nature and it is probable that it might have been a pesticide. However, the exact agent could not be identified because the quantity of sample from the case was insufficient. The two women are likely to have the same cause of illness but no epidemiological linkage is found between them and other cases in other events.

Event 2:
One French woman, age 25, died on 19 January. She developed fever and other symptoms on 16 January before arriving in Chiang Mai where she checked in at Hotel “B” on 17 January with a female friend who remained well.

Based on the evidence gathered and the clinical presentations of the case, investigators and experts concur that the French woman had acute severe myocarditis (inflammation of all the heart muscles) that represents a sporadic case most likely due to a viral infection, rather than exposure to a poison. The clinical symptoms and inflammatory cells found throughout the heart muscle (confirmed in 3 different laboratories including two in Thailand and one at the US CDC) support this opinion. Although state-of-the-art tests were performed for many viruses and bacteria, no etiologic agent could be identified. There is also no epidemiological linkage with the other events.

Event 3:
a) One New Zealand woman, age 23, died on 6 February. Her two female traveling companions, both age 23 and also from New Zealand, fell ill but recovered. All three women stayed in the same room and developed severe vomiting on the morning of 3 February.

b) One Thai woman, age 47, a tour guide, was found dead in her room on the morning of 3 February.

The three NZ women had severe metabolic acidosis (abnormal acid level in circulation) and two of them suffered myocardial injury (injury to the heart muscle). Clinical symptoms of the Thai woman are unknown since she was found dead in her room. Forensic autopsy found nothing abnormal only a 40% occlusion of the right coronary artery. It is probable she died from sudden arrhythmia (abnormal rhythm of the heart beat).

The women grouped in this event stayed at Hotel “C”. The Thai tour guide was in a room adjacent to that of the three NZ women. The investigation found that it is very likely the cause of the illnesses of these four women is the same given the timing of the onset of their illness and the proximity of their rooms. The cause is unlikely to be bacterial or viral. 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.

The clinical manifestation in the three NZ women, who were all hospitalised, can be explained by exposure to some chemicals such as those found in pesticides.

It should be noted that tests on blood and biological samples from the three NZ patients at US CDC and German laboratories returned negative results for suspected chemicals such as sodium monofluoroacetate (compound 1080) and phosphine gas. However negative results from some of these toxic substances do not necessarily confirm their absence as sometimes the suspected chemical is difficult to detect or dissipates easily from the biological specimen. Tests on the two rooms of the NZ and Thai women found aluminum molecules on carpet samples but it can not be definitively concluded that these came from pesticide containing aluminum phosphide. The aluminum molecules could have come from the paint on the walls and ceilings or from fluids used to clean air-conditioning units. Aluminum is an ingredient in paint and air-conditioning cleaning fluids and aluminum molecules were also found in other rooms sampled including that of the hotel manager.

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