The reopenings of US college campuses appear to have fuelled thousands of Covid infections and hundreds of deaths nationwide, scientists tracking?mobile phone records have concluded.

The number of campus-related infections ? estimated by the researchers at 3,200 per day for the first two weeks of the autumn semester ? would translate under US mortality averages to about 90 additional deaths each day.

The spread is largest in communities with institutions that both allowed students back to campus and offered in-person instruction, said one of the study¡¯s authors, Ana Bento, an assistant professor of epidemiology and biostatistics at Indiana University Bloomington.

Professor Bento and her colleagues??to medRxiv, a site for sharing research ahead of formal peer-review processes, as growing numbers of US institutions?suspend or cancel classes?in response to sustained Covid outbreaks.

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Her co-authors are professors of health, economics and higher education from Indiana, the University of Washington?in Seattle, the University of North Carolina at Greensboro and Davidson College.

Their numbers help affirm a separate??by?The New York Times, which has counted more than 88,000 infections on US college campuses since the pandemic began.

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Reports from various campuses have largely blamed the outbreaks less on classroom encounters than on non-academic student gatherings in dormitories, fraternities and off-campus restaurants and housing.

The study posted to medRxiv does not directly address that question. It does, however, show infection rates rose in communities as students returned ? and did so faster in places where in-person classes were offered.

By tracking GPS signals, the study authors showed that cellular device counts rose 54 per cent around campuses offering face-to-face instruction versus 33 per cent in communities where their institutions taught primarily online.

While exact locations of virus spread cannot be shown in the data, those comparative percentages offer strong evidence that colleges helped worsen the pandemic by encouraging students to return to their campus communities, Professor Bento said.

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That increased spread is likely to have repercussions beyond the additional 3,200 cases a day estimated by the study, Professor Bento said. ¡°You have to realise that for every case you record, you should expect a length of a chain of transmission behind it,¡± she said. ¡°We should expect far more cases, in fact, as a consequence of this event of opening the colleges and universities.¡±

A separate study by researchers at Louisiana State University (LSU), also using cellular data to estimate community-specific Covid spread, helped demonstrate the??practices.

The?LSU study, published in?PLOS One, did not specifically examine college campuses, said one of its authors, Rajesh Narayanan, a professor of finance at LSU. But the study does hold out for colleges the lesson that using cell-phone data to track social-distancing behaviours could help institutions issue more timely warnings to students engaged in risky practices, Professor Narayanan said.

paul.basken@timeshighereducation.com