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

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Two separate rounds of environmental experiments on the air quality in their rooms were also carried out to test the theory of poisoning by carbon monoxide, sulphur dioxide, nitrous oxide and nitrous dioxide as the women stayed at the hotel during Chinese New Year when incense and ritual burning of silver and gold paper was carried out by a neighbouring shrine. The experiments resulted in only a small amount of these gases entering the rooms and experts agreed that this should not have caused their illness.

Event 4:
An older couple from the United Kingdom – man (78) and woman (74) – was found dead in their room on the afternoon of 19 February. Consequently their clinical symptoms were unknown. Forensic experts estimated the time of death to be between 17-18 February. Autopsies and standard panels of tests for chemical, drug and pesticide were performed but found nothing abnormal. There is evidence of 40-80% occlusion in three coronary arteries in the man, and 30-60% occlusion in the woman. It is not unusual for older people to die from cardiac arrest but it is uncommon for a couple to die of this at the same place and around the same time,

As they also stayed at Hotel “C” albeit on a different floor to that of the women in Event 3, the possibility that the cause of this event is related to Event 3 cannot be excluded.

Investigation Constraints
As most of the deceased were foreign nationals and there were no evidence of a criminal cause, their bodies were quickly turned over to relatives who took them home. Some relatives also did not want an autopsy to be performed, consequently biological samples were limited and were insufficient for the large number of tests that had to be undertaken.

In addition current laboratory technologies to detect many toxins are subject to certain limitations, especially given the time lag between the deaths and arrival of samples at laboratories. Certain tests also require that samples be taken by a particular method and stored and transported in special containers. This was not possible because the need for testing for these toxic causes were not foreseen at the time of death.

What the findings mean?
Despite the best efforts of the Thai authorities and their international partners in undertaking an exhaustive investigation, the specific agents that caused the deaths and illnesses in these events can not be identified and it can not be determined exactly how people were exposed to them.

However, the investigation team and the panel of experts agree that available evidence suggests the following:

1. Event 1: the two cases in this event, an American and a Canadian woman, have similar clinical manifestations as those of the three NZ women in Event 3. Although there is a possibility that these two events might have the same causative agent, investigators cannot find supporting evidence.
2. Event 2: the illness and death of the French woman is not related to any other cases or events. It is a sporadic case of myocarditis most likely of viral origin.
3. Event 3: the four women, three New Zealanders and one Thai, are most likely to have the same cause of illness, probably exposure to some toxic chemical, pesticides or gas, but the agent can not be identified.
4. Event 4: this event, involving the older English couple, is possibly related to Event 3 as they occurred in the same hotel but again laboratories could not establish a direct link or the specific cause.

Investigators spent five months pursuing numerous hypotheses about potential causes. More than 350 drug, chemical and organism tests were done in each fatal case and more than 1250 tests were done on the New Zealand case. These tests were done in laboratories both in Thailand and overseas and a large number of personnel in Chiang Mai and Bangkok, as well as from the WHO and US CDC, worked on these events. However, as difficult as it may be to accept, the precise cause cannot be confirmed.

Actions taken by Thai authorities to reduce future risks

Thai authorities are taking measures to reduce the risks of chemical and pesticide exposure to future visitors to Chiang Mai and will also apply to other provinces in Thailand;

1) A panel will be set up to investigate and recommend stricter measures for the use of chemicals including pesticides in hotel and market areas.
2) A channel to receive notification of illness of tourists and expatriates has been set up. Visitors can post their notification at Chiang Mai Provincial Public Health or call 053-216592. Events will be verified and investigated.
3) Surveillance of hospitalised tourists, already in effect, will be continued and a new protocol for investigation of fatal cases is being adopted.
4) Retailers of household and agricultural chemicals (pesticides) must declare a watch list of products whose procurement and sales are to be closely monitored. The provincial health office will carry out periodic checks on them.
5) Hotel operators must use only licensed pest control companies and their contracts must specify which chemicals are to be used and samples collected and sent for testing by the authorities twice a year.
6) Municipal authorities are to give safety advice and monitor public celebrations where the burning of ritual papers and other materials are performed in communities, temples and shrines as part of traditional festivals.
7) Develop the food safety standard at eateries and among street vendors, especially around the Night Bazaar area, frequented by tourists in Chiang Mai.
8) Health Education Cards to advice tourists about food safety and other health concerns will be made available to foreign visitors to the province.
9) The Ministry of Public Health will apply these measures to safeguard tourists in other provinces.

Additional information on these events – Timeline of events, Frequently Asked Questions (FAQ), Roles & Responsibilities of Partners – are published on the website of the Department of Disease Control.

Any persons who may have specific medical or public health concerns about this event are invited to report them or make queries using this email address: [email protected].

The investigation team would like to express their appreciation and thanks to the following agencies for their assistance in this investigation: The provincial health office in Chiang Mai; the Forensic Department of Chiang Mai University; the Pathology Department of Chiang Mai University; the Toxicology Centre of Ramathibodi Hospital, Mahidol University; the Faculty of Dentistry, Mahidol University; the Department of Medical Science, Ministry of Public Health; the Department of Disease Control, Ministry of Public Health; the Faculties of Medicine, Science and Agriculture, Chiang Mai University; Central Laboratories, Ministry of Agriculture and Cooperatives; Osaka University; the International Health Regulation (IHR) Focal Point of New Zealand; the IHR focal point of the USA; the IHR focal point of France; the International Emerging Infectious Disease Programme of the Thai and US CDC Collaboration; the US Center for Diseases Control and Prevention; and the World Health Organization.


Related: Chiang Mai tourist death probe finds no common link

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

Related: Timeline of events related to the investigation and deaths of tourists in Chiang Mai

Related: Roles and responsibilities of key partners in the Chiang Mai tourist death investigation

Related: Frequently asked questions relating to the investigation into a cluster of tourist death in Chiang Mai

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