On March 19, the day the Trump administration urged Americans to stop traveling internationally, a group of students from the University of Texas at Austin returned from a spring break trip to a Mexican beach resort.
Within two weeks, 60 of the 183 travelers to Cabo San Lucas, along with four contacts, tested positive for the novel coronavirus, according to a report from the Centers for Disease Control and Prevention.
As students prepare to return to many universities this fall, the case study offers a window into how easily the virus spreads among college students — and how it can be contained. Researchers likened their close quarters and constant interaction to the environment of a nursing home in the potential for disease spread.
“Contact tracing and testing of close contacts, regardless of symptoms, is important in limiting spread, especially in young and healthy populations living in shared housing,” they wrote.
That effort limited the outbreak in this case, as did a local shelter-in-place order issued by Austin on March 25, six days after the students returned, the researchers concluded.
As schools reopen, “we need to have resources in place to be able to act and respond to these clusters,” including for people in isolation, said Darlene Bhavnani, an infectious-disease epidemiologist at UT-Austin’s Dell Medical School and the lead epidemiologist on the school’s contact-tracing efforts.
At the time, reports of positive cases provoked outrage among local leaders.
“It’s time to grow up,” Texas House Speaker Dennis Bonnen (R) said. “That is grossly irresponsible.”
Parents of some students defended their decisions to allow the trip, saying they were told by the travel company JusCollege they could not get refunds if they canceled because there was not yet a travel advisory to avoid Mexico.
“We take the safety of our customers very seriously and worked with public health authorities to assist with contact tracing where we could,” said a spokeswoman for JusCollege. “It was an unprecedented and rapidly evolving situation, and our communications to our customers were being updated in line with the changing U.S. government guidelines.”
The school began its investigation on March 28, after three of the travelers tested positive. They quickly identified the trip as a source of the outbreak through contact-tracing interviews. Although the first patient did not experience symptoms until the trip was over, some in the group became ill while in Mexico.
“Symptoms were mild in most cases,” Bhavnani said. “It was allergy season here, so a lot of people told us they weren’t really sure” whether they were sick.
Working with public health authorities, the school identified 298 travelers and close contacts and interviewed all but nine. Asymptomatic travelers and their contacts were advised to self-quarantine and monitor themselves for symptoms for 14 days. Symptomatic travelers and their contacts were offered tests and told to self-isolate until they got a negative test result, or for seven days after their symptoms began and three days without a fever. Ultimately, 231 people were tested.
But after half of the first batch of tests came back positive, the school decided to test anyone who had traveled to Cabo. Beyond April 2, two weeks after the travelers returned, testing continued only for symptomatic travelers and contacts. The investigation ended April 5, when the last symptomatic contacts got negative test results.
Bhavnani said the insular nature of the group helped contain the spread — “people would name each other as contacts, over and over again.” The travelers were sharing hotel rooms during the trip and dorms or houses after their return to Austin. About 90 percent took chartered planes to Mexico together, according to Bhavnani; the rest took private jets or commercial flights.
The median age in the group was 22. Although 78 percent of those who tested positive experienced symptoms, none required hospitalization, and none died. The most common symptoms were cough, sore throat, headache and loss of sense of smell or taste.
“Asymptomatic persons or those with mild symptoms likely play an important role in sustaining SARS-CoV-2 transmission during outbreaks, especially in younger populations, such as the one described here,” the researchers wrote.
Half of those who tested negative also experienced symptoms. The researchers suggest that those patients may have lied about symptoms to get a test early in the investigation or contracted a flu variety going around at the time. They also note that coronavirus tests have a false negative rate of up to 29 percent. Most students were tested only once, so some cases might have been missed.
“That was actually a limitation because we were not able to test over time,” Bhavnani said. “It could have been the case that someone’s result would have been positive later.”