The Penn team, which published its Cuba findings February in the Journal of the American Medical Association, was not able to prove what caused the symptoms in those patients.
"Symptoms to be attentive for include dizziness, headaches, tinnitus, fatigue, cognitive issues, visual problems, ear complaints and hearing loss, and difficulty sleeping", the warning stated.
The U.S. government has deemed the Cuba incidents "specific attacks" on American workers but hasn't publicly identified a cause or culprit.
More recently, U.S. diplomats in China also complained of symptoms similar to the ones suffered by colleagues in Cuba.
Cuba released details Sunday on the latest mysterious health incident involving a US diplomat in the country, saying that Cuban officials learned of the episode late last month when the USA said that an embassy official felt ill after hearing "undefined sounds" in her home in Havana.
The US embassy in China issued a new health alert for its citizens on Friday after more US government employees were evacuated from the country over fears they may have been hit by a mysterious illness.More news: The New Command and Conquer
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Two more people from the U.S. Embassy in Havana are undergoing medical evaluation, a State Department spokeswoman said on Friday, after a mysterious illness began to affect U.S. personnel and family members there since late 2016. "Instead, move to a different location". The U.S.is also examining new potential cases from a U.S. consulate in China. Most of the incidents were accompanied by freakish, unexplained sounds that initially led USA investigators to suspect a sonic attack.
Chinese Foreign Ministry spokeswoman Hua Chunying said on June 7 that as far as she was aware there had not been any formal communication between the two countries on any new cases.
People working in The Canton Place complex, a few kilometers (miles) from the consulate, said they were just hearing about the incidents, reflecting a lack of coverage in China's entirely state-controlled media.
The alert comes as a US medical team is screening more Americans who work at the Guangzhou consulate.
In April, Canada, whose personnel were also stricken, said it would remove families of diplomats posted at its embassy in Cuba as information from medical specialists has raised concerns of a new type of brain injury.