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U.S. colleges could be COVID-19 superspreader sites, and the first two weeks of classes are the most dangerous, researchers warn.
They studied 30 campuses nationwide with the highest numbers of reported coronavirus cases and found that more than half had spikes that peaked well above 1,000 cases per 100,000 people per week within the first two weeks of class.
On some campuses, 1 in 5 students had been infected with the virus by the end of the fall term. Four of the schools had more than 5,000 cases.
On 17 of the campuses, computer modeling showed that college outbreaks were also directly connected with infection peaks in the counties where the schools were located.
Luckily, the researchers also found that strict management of outbreaks -- such as immediately switching from in-person to online learning -- can lower infection peaks within about two weeks.
The study was published Jan. 13 in the journal Computer Methods in Biomechanics and Biomedical Engineering.
When compared to peak incidences of 70 to 150 per 100,000 people per week in the first and second waves of the COVID-19 pandemic, the rate of 1,000 cases per 100,000 people per week found in the study shows that colleges are at high risk for extremely high rates of infection, said lead author Hannah Lu, of Stanford University's Energy Resources Engineering program.
"Policymakers often use an incidence of 50 COVID-19 cases per 100,000 people per week as a threshold for high-risk counties, states, or countries. All 30 institutions in our study exceeded this value, three even by two orders of that magnitude," Lu said in a journal news release.
"The number of students who had become infected just throughout the fall is more than twice the national average since the beginning of the outbreak of 5.3%, with 17.3 million reported cases at a population of 328.2 million," she noted.
For example, all 12,607 students at the University of Notre Dame were tested before the beginning of class and only nine tested positive. Less than two weeks into the term, the seven-day incidence was 3,083.
"However, with around 90 reported deaths nationwide, mainly college employees and not students, the campus-related death rate of 0.02% remains well below the average death rate of COVID-19," Lu said.
A limitation of this study is that the actual on-campus student population was often unreported and had to be estimated by the total fall quarter enrollment.
"This likely underestimates the real maximum incidence and the fraction of on-campus students that have been affected by the virus," the study authors wrote.
"Strikingly, these local campus outbreaks rapidly spread across the entire county and triggered a peak in new infections in neighboring communities in more than half of the cases," said senior study author Ellen Kuhl, the Robert Bosch Chair of Mechanical Engineering at Stanford.
"Our results confirm the widespread fear in early fall that colleges could become the new hot spots of COVID-19 transmission. But, at the same time, college administrators should be applauded for their rapid responses to successfully manage local outbreaks," Lu said.