South Korea confirmed four more cases of novel coronavirus infections Thursday, bringing the total here to 23, with one case being a person who initially tested negative for the illness but was found to be infected later in a check-up.

The Korea Centers for Disease Control and Prevention said of the four new cases, three are believed to be person-to-person transmissions involving South Korean nationals, with the other one being a Chinese woman who arrived in the country on Jan. 23.

The public health agency called for more attention to be paid to people who have already been screened.

The agency said the 20th patient -- a 41-year-old woman who is a relative of a Korean man who was confirmed to have been infected Sunday -- initially tested negative for the virus, but when she was tested again when she started feeling unwell, she turned out to have been infected.

Her relative is the 15th person to be diagnosed with the virus.

He had traveled to Wuhan, the epicenter of the current outbreak, last month.

The 21st case is a 59-year-old woman who came into contact with the country's sixth patient, who in turn got the illness from a person who recently visited China. This person also infected his wife and son.

The 22nd person is a family member of the 16th patient who had visited Thailand recently.

The KCDC said that all three South Koreans had been in self-quarantine before being diagnosed with the virus. All the newly confirmed cases have been moved to proper quarantine hospitals so they can be monitored and treated.

It also said that all of the 22 people presently in quarantine after having been confirmed to have contracted the virus are in stable condition. One patient was discharged from a hospital after he was determined to be cured, with a second patient to be discharged later in the day.

The second person to be released is a 35-year-old Chinese woman who had come from Wuhan. She was diagnosed with the novel virus on Jan. 20, becoming the first confirmed case of the illness in South Korea. She was treated for pneumonia but has since made a full recovery.

Of the confirmed cases, four are Chinese nationals diagnosed with the coronavirus in South Korea, eight are South Koreans confirmed to be infected after returning from China, two are South Koreans who contracted the virus after visiting Singapore, one is a Korean confirmed to be infected after touring Thailand and the remaining eight are people who were contaminated in the country.

The public health agency said it is tracing the steps of the latest confirmed cases. More details on the four cases will be made available as soon as possible.

Since Jan. 3, the public health agency has screened 885 people and quarantined over 169 people for detailed check-ups for the novel coronavirus. Currently, there are 1,234 people who may have come in contact with infected people in self-quarantine, and they are being monitored carefully for signs of the illness. (Yonhap)