Austin, Texas, health officials are investigating a cluster of at least 28 confirmed coronavirus cases after a group of young adults returned from a spring break trip to Mexico.

The Austin Public Health Department confirmed in a Tuesday statement that earlier this month, about 70 adults “in their 20’s” chartered a plane for a spring break trip to Cabo San Lucas. Following their return, 28 have tested positive for COVID-19 and dozens more are “under public health investigation.”

Four of the confirmed cases did not present any symptoms before testing positive. Some of the people in the group returned to the U.S. on commercial flights.

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The 28 confirmed patients are self-isolating, according to the department’s Tuesday statement. The department has contacted all of the spring breakers who went on the plane and are monitoring them.

The University of Texas at Austin confirmed to NBC News in a statement that many of those on the trip are students there. They called the incident a “reminder of the vital importance” of abiding by public health warnings.

The Centers for Disease Control and Prevention (CDC) has recommended that Americans avoid all nonessential travel during the pandemic, as well as generally avoiding groups larger than 10 people.

“A leisure vacation of any kind is not considered essential,” the Tuesday statement said.

“The virus often hides in the healthy and is given to those who are at grave risk of being hospitalized or dying,“ Austin-Travis County Interim Health Authority's Dr. Mark Escott said Tuesday. “While younger people have less risk for complications, they are not immune from severe illness and death from COVID-19.”

This isn't the first time that spring breakers have earned the ire of public officials amid the outbreak. A video from Miami released by CBS News went viral earlier this month featuring college students saying that health officials are “doing way too much” and telling the outlet “If I get corona, I get corona.”

The University of Tampa in Florida announced last week that multiple students tested positive for coronavirus after traveling with other students on a spring break trip.