A man in his 50s who had mild symptoms of the coronavirus was found dead in his room at a hotel which was being used as a quarantine facility in Atsugi, Kanagawa Prefecture, on Friday night.

Prefectural health officials held a news conference on Saturday at which they said the man, who was found in his room in a state of cardiac arrest, died of acute bronchopneumonia, Fuji TV reported. The man’s death is one of the few cases in Japan of someone with mild symptoms dying while recovering in a quarantine facility with medical personnel on duty.

Prefectural health officials said the man, who had no known pre-existing medical condition, was diagnosed with the coronavirus on Dec 4 and admitted to the hotel on Dec 9. At the time, he told doctors he was suffering muscular and joint pain.

Medical personnel at the hotel check with occupants about their condition on the messaging app Line each day at 8 a.m. and 3 p.m. On Dec 11, at 8 a.m., the man said he had a headache and felt fatigued. At 3 p.m. and again at 4 p.m., he failed to respond either on Line, his mobile phone or room phone. One more call was made at 6:30 p.m. but the man did not pick up his phone.

However, medical personnel did not go to his room until 8 p.m., at which time the man was unconscious. He was taken to hospital where he was confirmed dead.

At the news conference, prefectural health officials apologized for the fact that staff did not immediately check to see if the man was alright. They also said they are investigating to see why a doctor was not called to see the man when he complained about pain and fatigue during his 8 a.m. call.