In October, a State Department official said the USA had "received a handful of reports from US citizens who report they experienced similar symptoms following stays in Cuba".
United States officials have issued a health alert in China following the incident.
That study found that 21 US government employees in Havana experienced "persistent cognitive, vestibular, and oculomotor dysfunction, as well as sleep impairment and headaches, were observed. associated with reports of directional audible and/or sensory phenomena of unclear origin". On May 18, the embassy learned that the diagnosis was mild traumatic brain injury.
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.
The U.S. government said it is taking this incident "seriously".
The Chinese foreign ministry could not be immediately reached for comment.
Dr. Charles Rosenfarb, the State Department's medical director, told a Senate subcommittee in January that the employees "associated the onset of these symptoms to their exposures with unusual sounds or auditory sensations".
"The US government is taking these reports seriously and has informed its official staff in China of this event", it said.
The State Department's health advisory noted the cause of the symptoms is unknown.
Officials initially suspected the Americans had been targeted by an acoustic weapon, but media reports have suggested that the Federal Bureau of Investigation has been unable to verify any evidence to support that theory.
The State Department said in its Wednesday statement that anyone who experienced "unusual acute auditory or sensory phenomena" while in China should move away from the source of the noise.
Multiple workers in Havana complained of an incapacitating "high pitch beam of sound".
While the USA has accused China of engaging in unsafe attacks on American personnel, including using lasers to harass and blind American pilots operating off the coast of Africa, there is now no evidence that China is involved in the incident, which has not yet been identified as an attack.
Of the 21 medically confirmed United States victims, some have permanent hearing loss or concussions, while others suffered nausea, headaches and ear-ringing.