College reopenings could be to blame for 3,000 new coronavirus cases per day in the US

• College reopenings appear to be fueling the recent uptick in US coronavirus cases.
• According to new estimates, which are still awaiting peer review, reopening colleges for in-person classes has added more than 3,000 new daily cases to the US tally.
• Overall, cases have spiked dramatically among people in their 20s, according to a new CDC report.

Once again, the hopeful trend in the US's coronavirus outbreak didn't last. Although the country's weekly average of coronavirus cases began dropping in July, new daily cases have risen by nearly 15% over the past week, according to data from Pantheon Macroeconomics.

The uptick isn't surprising, experts say. Many US colleges welcomed students back in late August. Even before classes officially started, outbreaks were recorded among student athletes, linked to fraternity parties, and traced to crowded local bars near campuses.

New research attempts to quantify the link between college reopenings and the recent uptick in the country's COVID-19 cases. According to that math, resuming in-person classes at colleges has added more than 3,000 new coronavirus cases per day to the US tally since July.

The study, which was released as a preprint and isn't yet peer reviewed, traced cell-phone activity across nearly 780 counties with college campuses from July 15 to September 13. The researchers then compared that data to confirmed COVID-19 cases during that time period.

"Colleges are bringing people together from all over the country and that's creating this mixing environment," Martin Andersen, a coauthor of the new study, told Business Insider. "Whenever you have mixing or this increase in flow, you would expect to see a potential for increased disease transmission."

Classrooms probably aren't the main culprit

Public-health experts say it often takes about two weeks for a coronavirus case to become part of the official total, since infections take five days to manifest in symptoms, on average. Then people usually wait a bit time before getting tested, and the results usually take at least three business days to come back.

That explains why college outbreaks are being reflected in the data we see now, but didn't immediately lead to a bump in the first days after classes resumed.

"It takes a little while for these effects to show up," Andersen said. "It's not like a campus reopens and immediately there's a spike in COVID-19 cases."

Andersen's research found that in the two weeks after college classes started, the average number of cell phones on a given campus rose by 47% compared to the two weeks prior. The increase in the number of cell phones was higher on campuses that resumed in-person classes: around 56%. Campuses that continued primarily with online learning only saw a 33% jump in the number of cell phones — probably because some students still returned to the dorms or local apartments, and teaching staff may have returned to campus as well.

But the researchers don't think classrooms are the epicenter of transmission on college campuses. Instead, they think colleges that resumed in-person classes are probably also less likely to require masks, and perhaps more likely to allow fraternity parties or fans at sporting events.

"Sitting in a classroom with a mask and instructor in a mask — we don't think that's a big opportunity for COVID-19 to be spread," Andersen said. "So it's probably these other things that are happening, you know, the college parties, the dorms, et cetera."

He noted, however, that his current data doesn't prove that yet.

'Do not send them home,' Fauci says of infected college students

Other data supports the theory that colleges are driving recent coronavirus transmission in the US.

More than 81,000 coronavirus cases were recorded at colleges from late July to mid-September, according to data from The New York Times. A new report from the Centers for Disease Control and Prevention also found that people in their 20s accounted for 20% of all COVID-19 cases from June to August — the highest of any age group. That's a jump from May, when people in their 20s accounted for only 15% of cases.

Andersen said his study doesn't mean that reopening a college inevitably leads to an outbreak, though.

"Where you draw students from matters a lot," he said. "Counties with schools that draw students from higher-risk places or places where the incidence of COVID-19 is going up have disproportionately larger increases in case counts."

That means colleges should be able to reasonably assess the risks they take when bringing students back.

"They know where their students are coming from," Andersen said. "They can do the math better than we can about the profile of their incoming class and how risky that is."

If students are getting sick on campus, public-health experts say, colleges should not ask them to return home, since that could lead them to infect others.

"They should be able to accommodate the students in a facility, maybe a separate dorm or a separate floor, so they don't spread among the student body," Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, said at a Senate hearing on Wednesday. "But do not send them home to their community."