New York City health officials are investigating a cluster of coronavirus cases linked to the Electric Zoo music festival earlier this month.

Sixteen people have tested positive since attending the three-day music festival, according to a statement released Wednesday by the city's Department of Health and Mental Hygiene. A spokesperson for the health department said the cluster was defined as "people who attended during their potential exposure period," and did not stem from a single group of attendees. The agency did not immediately answer whether the positive cases involved unvaccinated individuals but said more details would be released in the coming days.

Investigators have identified another eight attendees who were positive and likely contagious when they were at the festival.

"If you are someone who was at the festival, even if only for one day or one event during the three days of the festival, we do encourage you to get tested," Health Commissioner Dr. Dave Chokshi said Thursday at a City Hall press briefing. "And that recommendation stands, regardless of your vaccination status. But it's particularly important if you've had symptoms."

The city didn't release an official estimate of the crowd size, but WNYC/Gothamist reported over Labor Day weekend that the long-running and widely popular outdoor rave likely brought tens of thousands of partiers to Randall's Island. Attendees were required to share proof of vaccination or a negative COVID-19 test within three days. While the coronavirus is less likely to spread outdoors, the risk isn’t zero, according to the Centers for Disease Control and Prevention. This safety net is eroded further when social distancing isn't followed outdoors.

Prior to this week's announcement, some concert-goers were already warning their fellow attendees about a rumored outbreak at Electric Zoo.

"It got out in our community that an individual had passed through security with a fake vaccine card and was positive for COVID," said Chris, a 25-year-old attendee from Queens, who declined to give his last name. "I was mad that the individual knew and still chose to attend, risking everyone else’s health."

He said he planned to follow the commissioner's guidance and get tested on Thursday, after waking up to several worried texts from his mother.

News of the cases follows a frustrating summer for the concert industry, as the highly contagious delta variant scuttled plans for a strong rebound. In recent weeks, several high-profile acts have delayed fall tour dates or moved away from indoor venues, while some festivals, including the New Orleans Jazz and Heritage Festival, have canceled entirely.

In Chicago, health officials estimated that 203 cases of COVID-19 connected to Lollapalooza last month. The city's Public Health Commissioner said those cases were in line with expected totals and would likely not have a major impact on infection rates.

Inquiries to Electric Zoo were not returned. Governors Ball, the music festival at CitiField, is scheduled for September 24-26. Its requirement for entry is either full vaccination or proof of a negative COVID test.