What is the health cost of opening college campuses during a pandemic, for students and the broader community? New data from the Centers for Disease Control and Prevention finally offers an answer to the question that has plagued higher ed leaders for the last 10 months.

Cases of COVID-19 increased 56 percent in U.S. counties with large colleges that hosted classes in-person early this fall, according to new analyses from the CDC, published Jan. 8. By contrast, counties with large colleges that held classes remotely saw a nearly 18 percent drop in cases.

Here’s how the CDC tallied the results. Researchers looked at nonprofit colleges around the country that enroll at least 20,000 students, and matched the institutions with their host counties. In 22 counties, large colleges started the fall semester with remote classes. In 79 counties, institutions started with in-person classes. These 101 large-college counties account for almost a third of the U.S. population.

The CDC then compared virus incidence in each county during the three weeks before and the three weeks after classes started. Researchers also compared those results to case counts in about 3,000 counties that do not have large colleges. In those places, there was a 6 percent decline in COVID-19 cases during the same period.

Not only did large-college counties have a significant increase in COVID-19 cases—they also experienced a 30 percent increase in “hotspot occurrence,” meaning that case counts rose especially rapidly.

Some colleges that attempted in-person teaching required students to get tested, but that increase in testing rates does not explain the spike in case counts, the study says, because it was accompanied by increases in test percentage positivity.

The research has some limitations. It did not account for mask and social distancing requirements in counties or on college campuses. It could not determine whether the virus was spread in college spaces like classrooms and dorms, or in the broader community—although it does note that “congregate living settings at colleges and universities were linked to transmissions.” And the study does not consider whether the same trends would apply in the case of small colleges.

Still, study authors note their hopes that the research will “inform ongoing college and university operations and future planning” and emphasizes that “efforts to prevent and mitigate COVID-19 transmission are critical for U.S. colleges and universities.”

Read the full article about campuses opening during a pandemic by Rebecca Koenig at EdSurge.