(AP) — World Health Organization investigators have visited a research center in the central Chinese city of Wuhan that has been the subject of speculation about the origins of the coronavirus. The Wuhan Institute of Virology has extensive virus samples, leading to unproven allegations that it may have caused the original outbreak by leaking the virus into the surrounding community. China has strongly denied that possibility and has promoted unproven theories that the virus may have originated elsewhere. Over six days, the WHO team that includes experts from 10 nations has visited hospitals, research institutes and a traditional market tied to the original outbreak.