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Almost 30 students who recently traveled to Mexico for spring break have tested positive for COVID-19.

Health officials in Austin, Texas, on Tuesday announced an investigation into a "cluster" of COVID-19 cases among a group of roughly 70 people in their 20s who traveled in a chartered plane to Cabo San Lucas, Mexico for spring break about a week-and-a-half ago amid the coronavirus crisis.

"Currently, 28 young adults on this trip have tested positive for COVID-19 and dozens more are under public health investigation," the Austin Public Health Department said. "Four of the confirmed cases did not present any symptoms."

The 28 people who tested positive are currently self-isolating, and more are being monitored while quarantined, according to the statement. The University of Texas at Austin told NBC News that the 28 young adults with COVID-19 are students at the school. Some individuals who went on the trip came back home on commercial flights, according to the Austin Public Health Department's statement.

Austin officials said that although Mexico wasn't under a federal travel advisory when the young adults traveled there, "Austin-Travis County residents should follow CDC's travel recommendations indicating travelers avoid all non-essential international travel," and "a leisure vacation of any kind is not considered essential." The University of Texas at Austin told NBC that this serves as a "reminder of the vital importance" of following health officials' warnings amid the coronavirus pandemic.