In an email he shared with The New York Times, a disease intervention specialist with the Hawaii Department of Health did not confirm that Mr. Fujiwara’s friend was the one who had been diagnosed, but told him that he should contact the department if he had any symptoms before Tuesday, which would be two weeks after he saw his friend — the maximum incubation period for coronavirus.

Mr. Fujiwara said, “I plan to go to dinner with my girlfriend tonight, unless things change, specifically because I have it in writing from the State of Hawaii Department of Health to continue my daily routine.”

Janice Okubo, a spokeswoman for the Hawaii Department of Health, said that the man who was confirmed with the virus “is not believed to have had any prolonged, close contact with Hawaii residents,” but that health officials were continuing to investigate.

Dr. Sarah Park, the state epidemiologist, said the man had most likely been exposed to the virus before leaving Japan or while traveling to Hawaii. He and his wife, who was also confirmed on Saturday with the virus but did not show symptoms while in Hawaii, arrived on Maui on Jan. 28. The man was also symptom-free in Maui, but after the couple moved to Honolulu, on Oahu, on Feb. 3, he began showing signs of a cold.

A spokeswoman for Hilton Grand Vacations, which runs the hotel and time-share where the couple stayed in Waikiki, said the company was working with health officials. A letter slipped under the door of vacationers’ rooms provided tips on how to keep from getting the virus, washing hands being chief among them.

The man who became ill wore a mask when he was outside and while on the flight back to Japan, officials said, and was diagnosed with pneumonia, and later with coronavirus, after returning to the couple’s home in Nagoya, Japan’s fourth-largest city.