A man confirmed to have COVID-19 was found to have visited clubs in Itaewon, one of the popular nightlife districts in Seoul, authorities said Thursday, triggering concerns about the community spread of the virus.

The 29-year-old man, who lives in Yongin, Gyeonggi Province, has the first domestic infection reported in South Korea in four days. Most new cases over the past week have come from overseas.

How and where the patient contracted the virus remain unknown, raising fears that the virus may be spreading in communities undetected. He had no known contact with previous patients and he had not come into contact with anyone who recently returned from overseas, according to the initial epidemiological study.

The patient, who works at a software company in Seongnam, Gyeonggi Province, began to show symptoms -- high fever and diarrhea -- Saturday, visited a local clinic Sunday and got tested Tuesday.

According to the information on his movements released by the authorities, he visited at least three nightclubs in Itaewon during the country’s long holiday, as well as a restaurant, supermarket, clinic, shop and pharmacy.

The Itaewon clubs he visited Friday night and early Saturday had several hundred visitors within the same time frame, which put authorities on alert.

A 31-year-old Anyang City resident who accompanied him on the trip to Itaewon also tested positive, the Anyang City government said Thursday.

Including the Yongin resident, Korea reported four new COVID-19 cases in the 24 hours ending 12:01 a.m. Thursday, three of which were imported, according to the Korea Centers for Disease Control and Prevention. The total number of coronavirus cases here stands at 10,810. The Anyang resident’s case is not included in the most recent 24-hour tally but will be part of the next update, to be released Friday.

The number of new confirmed cases on a daily basis has stayed below 20 for 20 consecutive days, and under five since Tuesday, leading the government to ease its social distancing campaign starting Wednesday.

Despite the slowdown in infections, health authorities are on alert over cases in which the source of infection remains unknown, over fears of mass infections.

By Ock Hyun-ju (laeticia.ock@heraldcorp.com)