The agency emailed a notice to all US citizens in China about the employee at the consulate in Guangzhou who said there were “subtle and vague, but abnormal, sensations of sound and pressure”. It advised Americans to contact medical professionals if they experience any “unusual auditory or sensory of phenomena accompanied by unusual sounds or piercing noises”.
The incident harkens back to when nearly two dozen US employees working in Havana had sought medical treatment between December 2016 to May 2017 for headaches, ear pain, dizziness, and hearing issues.
Symptoms, sounds and sensations reportedly varied dramatically from person to person. Some have permanent hearing loss or concussions, while others suffered nausea, headaches and ear-ringing. Some are struggling with concentration or common word recall, The Associated Press has reported.
A subsequent FBI investigation did not reveal evidence of a “sonic attack”.
However, the reports put the largest strain on US-Cuba relations since former president Barack Obama forged closer ties in 2014.
Between September and October 2017, US President Donald Trump expelled 17 Cuban diplomats from the US, ordered US staff in Havana to come back, and issued a travel warning to the small, island nation - all implying the administration believed Cuba had some role in the mysterious illnesses of the diplomats.
Cuba, for its part, denied any wrongdoing and attributed the illnesses to a possible psychological cause.
The State Department said it is not aware of any similar situations in China and did not identify the person who reported the systems or when that information was relayed to the agency.
Jinnie Lee, a spokeswoman for the United States Embassy in Beijing, told the New York Times that the employee in question “reported experiencing a variety of physical symptoms” from late 2017 until April of this year.
“The embassy was told that the clinical findings of this evaluation matched mild traumatic brain injury,” Ms Lee said, but stopped short of further details in order to protect the employee’s privacy.
Ms Lee indicated the Chinese government is also investigating the matter. Nearly 2,000 US employees are stationed in the country and are closely watched by Chinese security.
The report comes at a crucial time in US-China relations as well. Trade negotiations between the two economic giants are taking place as well as preparations for an upcoming summit between Mr Trump and North Korean leader Kim Jong-un.
China has deep connections with North Korea – Pyongyang has long relied on it and Russia for basic economic needs along with a small number of other allies. However, China’s recent enforcement of strict United Nations sanctions on seafood, textiles, foreign exchange services and fuel are believed to have hurt the hermit kingdom.