Dartmouth College officials, in a message to students, said an investigation was underway to trace the close contacts of the individual, and said no Dartmouth students were considered close contacts to the patient at this time. It was unclear whether the second patient who tested positive had attended the mixer or was exposed at another time.

“The general vibe is we are all pretty concerned that this medical professional showed up to the event, despite being told to self-isolate,” said Christie Harrison, a first-year Tuck student who sang with the band that performed at the mixer on Friday night. She estimated that about a hundred business school students attended, along with 30 or 40 resident physicians associated with Dartmouth-Hitchcock, an academic medical center located near Dartmouth College.

“We all were just excited to have one of the last few parties of the quarter and be off campus,” Ms. Harrison said. She said investigators appear to have made efforts to trace those who interacted with the man at the mixer, and have asked them to self-quarantine. Those who did not interact with him, like herself, were simply told to monitor their health and alert authorities if they came down with symptoms, she said.

“The college was really great at communicating all of that to us, in a timely manner,” Ms. Harrison said. “The college has been really transparent with us throughout the process.”

Gunnar Esiason, a Tuck student who considered going to the mixer on Friday night, but did not, said he nonetheless felt distressed about the potential exposures because he has underlying health issues. “In my opinion, it is shocking that a health care worker would do this, if it is in fact true,” said Mr. Esiason. He has since left campus and was planning to take exams remotely.