US diplomats in two more Chinese cities have complained of symptoms similar to those suffered by victims of a suspected “sonic attack” in the southern city of Guangzhou. The latest incidents, in Beijing and Shanghai, come almost two months after a US government worker in Guangzhou experienced “abnormal sensations of sound and pressure” at home and was diagnosed with mild traumatic brain injury. The sickness is yet to be explained but one theory is that bugging devices emit sonic waves that cause dizziness, tinnitus and nausea. Beijing said that an investigation had uncovered no reason for the reported illnesses. One American from the consulate in Shanghai and two from the embassy in Beijing have been evacuated from China and sent home for medical examinations, according to The New York Times. Eight were evacuated from the consulate in Guangzhou several weeks ago. The US embassy in Beijing declined to comment.