On the morning of March 8, three days after the party, Julie Endich, one of the guests, woke up in Westport with a fever that spiked to 104 degrees and “pain, tightness and heaviness like someone was standing on my chest,” she later wrote on Facebook. She knew her symptoms suggested COVID-19, the disease caused by the novel coronavirus, but it would be four days before she could get test results confirming that she had it.