The party in mid-June was hosted by someone who was sick with coronavirus at the time, Rockland County Executive Ed Day told USA TODAY on Thursday.

It worked: All eight partygoers responded to the subpoenas, avoiding possible fines of $2,000 per day from Rockland County, the first known county in the state to resort to legal action amid this public health emergency.

The party in mid-June was hosted by someone who was sick with coronavirus at the time, Rockland County Executive Ed Day told USA TODAY on Thursday.

Rockland County Health Commissioner Patricia Schnabel Ruppert said at a Wednesday press conference that health workers tried to talk to people who tested positive after attending the party in an effort to contain the coronavirus cluster.

Hear the latest information about the COVID-19 cluster in Rockland County and how the health department is responding

Rockland County has reported more than 13,600 cases of coronavirus, with 668 deaths, as of Thursday night

"They were not answering the questions of our contact tracers," John Lyon, spokesman for the Rockland County Executive Office, told USA TODAY. "It's a very important part of this process so we can notify people and they can quarantine as a precaution so they don't spread this to other people beyond that immediate circle."

The county also used subpoenas during a measles outbreak last year and found success in tracing the outbreak, leading to a countywide vaccination mandate for the disease, officials said