OTTAWA, Canada (AFP) — An eight-month investigation failed to identify a cause of the mysterious illness that afflicted Canadian and US diplomats last year in Cuba, a senior Canadian government official said Wednesday.

The official said 27 Canadian diplomats and family members were tested after complaining between April and December of dizziness, headaches, nausea, nosebleeds or sleeplessness.

Eight people flew back to Canada for medical care from a group of military doctors, but none were hospitalised and none are believed to have suffered any permanent damage.

Three diplomatic families, however, have chosen not to return to Cuba out of concern for their wellbeing.

People are getting sick and nobody has any idea why, the official said, describing the situation as unique in the world.

However, he said it does not warrant the closure of Canada’s mission in Havana.

Ottawa said it also does not believe there are any risks for Canadian tourists in Cuba. Briefing reporters on the case, the official said a whole-of-government investigation led by the Royal Canadian Mounted Police (RCMP) in collaboration with US and Cuban authorities was unable to confirm US suspicions of a sonic attack, or even that a single cause was to blame for the symptoms.

Those who were afflicted included global affairs, immigration and national defense staff at the embassy as well as their spouses and children.

The last two cases in August and December involved individuals who claimed to have sensed what they described as waves of pressure.

Unlike their American counterparts who suffered injuries resembling brain trauma, however, no Canadian envoy reported hearing any suspicious sound prior to falling ill. One Canadian described hearing a high pitched noise like a sheet of metal being flexed, but they did not suffer any sickness.

Canadian authorities are currently conducting an environmental assessment that includes air and water tests at its embassy and staff residences in Cuba — but other leads have gone cold.

On Tuesday, in a hearing for the US Senate Foreign Relations Committee, State Department officials said they would open a review board into their own handling of the case, but offered frustrated American lawmakers little in the way of answers.

Initially US officials suspected the Americans had been targeted by some sort of acoustic weapon, although in public senior officials were more cautious, speaking of “health attacks.”

Now, US media reports suggest that FBI agents dispatched to Havana have not been able to find any evidence to support the acoustic or sonic weapon theory.