Photos of the festival show hundreds of people crammed in front of a stage under neon lights, dancing, hugging and practicing little social distancing.

Ms. Diaz, 42, got a fever on March 15. The next day her girlfriend was also sick. By the time Ms. Diaz was confirmed positive for Covid-19, she had been grocery shopping, gone to the pharmacy and spent time with her employer’s 80-year-old father and 14-year-old daughter.

“I understand that was my choice to be there — I take full responsibility for that,” Ms. Diaz, who lives in Wilton Manors, Fla., said of the Winter Party Festival, which drew about 5,500 people and has been a fixture in the L.G.B.T.Q. community for more than 25 years.

“I am really upset for the way it was handled,” she said.

Loc Nguyen, a software developer, felt exhausted from the time he returned home to Los Angeles from the festival on March 9. He went to work the next day but had to call in sick after that, feeling shortness of breath and such terrible shivers that he wrapped himself in three winter jackets to go to the doctor.

“You’re coughing and gasping for air,” Mr. Nguyen said. “You are scared. You can’t breathe.”

His friend who went to the festival with him also tested positive. A third friend got sick but was unable to get a test.

Mr. Nguyen knew the risk of attending, but said he did not want to lose the money he had spent on tickets. He did not blame organizers for holding the festival, and pointed to mixed messages from local officials.

“If one city closes and one city is open, it’s not consistent,” he said. “And therefore you can’t stop this pandemic.”