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Health officials believe the virus is likely to have spread to call centers since the end of last month, earlier than previously known. Authorities also believe that it is difficult to follow every one hundred close-up checkers now, and decided to quarantine the family or close contacts first.

This is reporter Nam Joo-hyun.

<Reporter>

During the epidemiological investigation, the city of Seoul confirmed a tester's statement that he felt the first symptoms of corona 19 last month.

It is more likely that the virus spread in the call center started at least two weeks ago.

The number of people who have contacted while the confirmed people are infected is bound to increase.

Health officials have admitted that epidemiological investigations that track the patient's movements are impossible because of the large number of confirmed patients and the distribution of copper routes throughout the metropolitan area.

[Eun-Kyung Chung / Head of Disease Control Division: I think it would be difficult to analyze the copper lines (as in the beginning) and to investigate a number of unspecified multi-use facilities.]

Instead, we hurriedly quarantined close contacts such as family members and inspected them, and we visited Korea Building after the 24th of last month and sent a letter to people who had suspected symptoms of corona 19 to be examined.

We are also in a hurry to investigate the call center environment.

[Eun-Kyung Chung / Head of Disease Control Division: There are several ventilation openings, and whether this is the ventilation of the entire building or whether it is being vented separately, we are currently investigating that.]

Health officials will determine if the ventilation system for ventilation is functioning properly and how the narrow and dense work environment has affected virus transmission.

(Video Editing: Choi Hye Young)