The US government issued an alert Wednesday following reports that a government employee stationed in southern China experienced “subtle and vague, but abnormal, sensations of sound and pressure” and sustained a brain injury.

The case draws clear and eerie parallels to mysterious health problems that affected US diplomats in Cuba , who also experienced unexplained episodes of unusual sounds and pressure followed by diagnoses of traumatic brain injury.

Responding to an email from the New York Times, a spokesperson for the United States Embassy in Beijing said that the unnamed employee was working in the US consulate in the city of Guangzhou, just northwest of Hong Kong, and experienced a variety of symptoms from late 2017 until April of this year. In statements to the BBC, she noted that the employee had been sent back to the US. Last Friday, the 18th of May, “the embassy was told that the clinical findings of [an] evaluation matched mild traumatic brain injury,” she wrote.

Symptoms of such an injury can include headaches, nausea, fatigue, dizziness, feeling dazed, and problems with speech.

In the US State Department’s alert, the government said that it isn’t taking any chances, despite the mystery around the episode:

The U.S. government is taking these reports seriously and has informed its official staff in China of this event. We do not currently 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 situation is similar to the enigmatic episodes and injuries seen in US government personnel, family members, as well as some Canadian officials stationed in Cuba. As Ars reported previously, from late 2016 to August 2017, 24 US individuals reported experiencing bizarre sonic and sensory episodes there, followed by a constellation of neurological symptoms. The episodes tended to include directional, irritating sounds , such as buzzing and piercing squeals, as well as pressure and vibrations. Extensive medical testing of 21 of the 24 affected US individuals concluded that they sustained “ injury to widespread brain networks .”

Guesses and notions of what could explain their experiences and injuries abound, including malfunctioning surveillance equipment and a covert sonic weapon. But no clear leading hypothesis has emerged, and US officials have not suspected foul play from Cuba or China in either case.

Still, the US government is on edge. The embassy in Cuba remains staffed by a skeleton crew, and a travel alert is still in place. For those in China, the government urges vigilance: “While in China, if you experience any unusual acute auditory or sensory phenomena accompanied by unusual sounds or piercing noises, do not attempt to locate their source. Instead, move to a location where the sounds are not present.”