For example, at the post-funeral reception at the retirement community in Rockville, authorities determined that only people who had physical contact with the infected person are likely to be at risk.

There are several factors behind a directive to self-quarantine, said Montgomery County health officer Travis Gayles. They include the type and duration of the interaction with the infected person and that person’s condition at the time of the interaction...

https://www.washingtonpost.com/local/dc-virus-christ-church-quarantine/2020/03/09/17567796-61fa-11ea-845d-e35b0234b136_story.html