For COVID-19, a close contact is anyone who you were within 6 feet for a combined total of 15 minutes or more over a 24-hour period.

An infected person can transmit SARS-CoV-2, the virus that causes COVID-19, starting 48 hours (2 days) before they have symptoms or their positive specimen collection date. Please note people who are infected but do not show symptoms (asymptomatic) and those who do not yet have symptoms (pre-symptomatic) can spread the virus to others. People who have been in close contact with someone who has COVID-19 should quarantine. People with recent exposure to COVID-19 who have been fully vaccinated may not be required to quarantine. People who were previously diagnosed with COVID-19 within the last three months may not be required to quarantine.

Source