The United States has also not yet revealed how many people are being evacuated.
China said last month that it had found no explanation.
"As for the latest incident, my understanding is that the United States side hasn't had any formal communication with the Chinese side about it", foreign ministry spokeswoman Hua Chunying said at a regular press briefing.
China's government said Thursday that it investigated and could not find anything to cause the described symptoms, NPR's Anthony Kuhn reports from Beijing.
In testimony before the Senate Foreign Relations Committee last month about the first case in China, US Secretary of State Mike Pompeo said China had "said all the right things and have demonstrated their willingness to help us identify the vector which led to this medical incident".
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A group of USA diplomats stationed in China have been brought back to the states after being inflicted by a mystery illness that reportedly resembles the brain injuries previously suffered by staff in Cuba.
A US government official there reiterated that there had been only one confirmed case in China, announced last month, and the State Department was offering screening to anyone in the USA embassy or consulates in China who requested it.
State Department spokeswoman Heather Nauert said "a number of individuals" had been brought to the U.S. but did not say how many were affected or evacuated.
"By far, we have found no reason or clue that would lead to the situation reported by the U.S. side", ministry spokeswoman Hua Chunying said. It's one of five consulates the USA operates in China, along with its main embassy in Beijing, according to the State Department's website. Lenzi said they began hearing odd sounds in April 2017, which he compared to rolling marbles with static. A few months later, he - along with his wife and their young son - started experiencing headaches that would sometimes last several days. That person reported abnormal sensations of sound and pressure before being diagnosed with a mild brain injury.
The Penn team said that the patients from Cuba experienced persistent disability, though rehabilitation therapy customised for them seemed to help. In response, it downsized the US diplomatic staff in Havana and prohibited families from joining the diplomats who stayed. UPenn professors published a study in February finding that a "novel mechanism" was used to attack the diplomats in Cuba, confirming that the symptoms were the result of real physical damage and were not psychosomatic or the product of paranoia.
But despite an investigation by the FBI that has lasted for more than a year, USA officials have been unable to determine the cause of the injuries, much less who the perpetrators might be.