Chiba Prefectural officials hold a news conference on the infection of a man in his 20s with the new coronavirus at the Chiba Prefectural Government headquarters in Chiba's Chuo Ward on the evening of Feb. 13, 2020. (Mainichi/Shohei Miyamoto)

CHIBA -- The Chiba Prefectural Government held a news conference on the evening of Feb. 13 after it was learned that a man in his 20s in the prefecture east of Tokyo had been infected with the new coronavirus, but officials were unable to pinpoint the source of his infection.

Reporters asked officials how the man had come to be infected, but local health crisis response official Shuichi Kubo was unable to provide details, repeatedly saying "We haven't linked it with a specific source of infection," "It's unclear," and "We don't know."

The man in his 20s is the sixth person in the prefecture confirmed to be infected with the coronavirus. However, his case is the first in which the source of infection remains unclear.

Health care official Masatoshi Watanabe, who was also at the news conference, appeared perplexed, commenting, "We're still investigating his recent actions, and we don't have any information ourselves."

(Japanese original by Shohei Miyamoto, Chiba Bureau)