"We do not now know what caused the reported symptoms and we are not aware of any similar situations in China, either inside or outside of the diplomatic community", the State Department warned in a health alert.
A US State Department employee has suffered "subtle and vague, but abnormal, sensations of sound and pressure" that later lead to a diagnosis of "mild traumatic brain injury" while working in China - resulting in a warning to all US citizens there. Ten Canadian diplomats and their relatives also suffered a odd illness.
"The US government is taking these reports seriously and has informed its official staff in China of this event".
"Twenty-four people have had symptoms and findings consistent with what looks like a mild traumatic brain injury", State Department medical director Dr. Charles Rosenfarb told a Senate Foreign Relations subcommittee January 9 "The findings suggest that this is not an episode of mass hysteria".
"We can not at this time connect it with what happened in Havana but we are investigating all possibilities", a USA embassy official in Beijing told AFP news agency on condition of anonymity.
The Chinese foreign ministry could not be immediately reached for comment.
In Cuba, the American victims had associated the onset of their symptoms with "unusual sounds or auditory sensations". "Instead, move to a location where the sounds are not present", the State Department advises. The State Department ultimately confirmed 21 cases in Cuba.
The employee experienced the symptoms from late 2017 through April 2018 while on assignment in the southern Chinese city of Guangzhou, where a US consulate is located, according to Jinnie Lee, a spokeswoman at the USA embassy in Beijing. Officials believe some type of sonic weapon may have been used.
The US government has held Cuba responsible, arguing that Raul Castro's authoritarian state must have either carried out the assaults or at least known who was behind them.
The US State Department expelled 17 Cuban diplomats from its Washington embassy a year ago after the incidents came to light.
The cause of those incidents remains unresolved.
The symptoms included dizziness, headaches and a lack of ability to concentrate.
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