Another U.S. Embassy employee in Cuba has come down with mysterious health symptoms consistent with those suffered by at least two dozen workers at the Havana compound, the State Department said Thursday.

Confirmation of the symptoms in a 25th embassy employee — one of two staffers medically evacuated from Havana — brings investigators no closer to determining exactly what happened since the first incident was reported in late 2016.

“We still don’t know, to this day, what is causing it and who is responsible,” said State Department spokeswoman Heather Nauert.

The second employee evacuated from Cuba is still being evaluated, Nauert said. Before this incident, the last time an embassy worker was known to have been affected was in August.

U.S. authorities are still investigating the confirmed cases in Cuba and one in China, where an employee at the U.S. Consulate in Guangzhou experienced similar symptoms. The Cuban government has denied any involvement, but U.S. officials have said Cuba is a “small island” and that they believe the government must know who the perpetrator is.

The stricken embassy employees in Cuba and China have reported health issues including concussions, hearing loss and disorientation after hearing odd, unexplained sounds. Many have been screened and treated by specialists in brain injury at the University of Pennsylvania.