The higher the use, the more footprints are available for health officials to track, which makes it more difficult to track elderly people who are typically more averse to paying with plastic.

Credit card use leaves digital footprints that health officials are using to trace the exact paths traveled by coronavirus carriers.

The Bank of Korea in a report last month said cash transactions accounted for just 19.8 percent of household spending as of 2018. That means eight out of 10 people use plastic.

Quarantine officials determine potential carriers by identifying everyone who came within a 2-m distance of an infected patient starting a day before he or she began displaying symptoms.

They are then narrowed down depending on whether the infected person was wearing a mask, sneezed or was in an enclosed area at the time. Those in the narrower group are then told to quarantine themselves for 14 days to see if symptoms appear.

The Korea Centers for Disease Control and Prevention use CCTV camera footage and credit card records to determine who comes into contact with a confirmed carrier.

Mobile phone records are also used, but they are less precise than credit card records.

The KCDC sends vital information about a carrier to credit card companies as well as the date when symptoms first appeared, and the companies send back usage data. By law, health officials do not need court approval or the consent of the carriers to obtain the information, in a national crisis like the spread of contagious diseases.