As nations reopen, warning emerges about coronavirus tracing voids

Authorities have cautioned that the scourge could come back with a vengeance without widespread testing and tracing of infected people’s contacts with others. Fears of infection spikes in countries that have loosened up came true in recent days in Germany, where new clusters were linked to three slaughterhouses; in Wuhan, the Chinese city where the crisis started; and in South Korea, where a single nightclub customer was linked to 85 new cases. The World Health Organization’s emergencies chief, Dr. Michael Ryan, said that robust contact tracing measures adopted by Germany and South Korea provide hope that those countries can detect and stop virus clusters before they get out of control.