Over the next week, more than 100,000 students in the State University of New York system will get tested for coronavirus. At Harvard, thousands more will do the same, as will students at the University of Wisconsin-Madison and the University of Michigan.

Colleges across the US are scrambling to secure tests for students ahead of Thanksgiving, a national migration that threatens not only to strain testing capacity but also become a mass superspreader event, according to public health experts.

The deluge of testing on campuses is just one front line of a surge in demand for testing as Americans hope to secure an “all clear” before congregating with family and friends.

The problem with that strategy, experts warn, is that tests may not pick up early-stage infections. Even if people test negative before travelling, they could still pick up the virus in transit, especially at hubs such as airports. If they contract the disease during Thanksgiving celebrations, they could transmit it to others while returning home.

“People are using testing as the primary wall between them being infected, but that is not going to work,” said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. “What does work is changing your behaviour.”

Test manufacturers have warned in recent weeks that their capacity to provide tests for everyone who wants one is under strain, as the country’s coronavirus outbreak continues to accelerate.

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The US has carried out an average of 1.3m tests a day over the past week and more than 1.8m on Thursday, according to a Financial Times analysis of Covid Tracking Project data. The American Clinical Laboratory Association say its members are carrying out a record 500,000 a day.

Quest, one of the largest companies selling diagnostic tests, said orders for its kits have increased by 50 per cent since the last week of September. This month, the company has already processed over 25m tests — more than in the whole of October, or any month since the pandemic began. Its main rival LabCorp said it is also experiencing a surge in demand.

The ACLA warned last week its members were suffering problems procuring vital supplies such as pipette tips.

Column chart of Seven-day average of Covid-19 tests, in millions, by geographic region showing Daily testing volumes in the US are at a record high

The prevalence of the disease, which is rampant across the US, has compounded testing companies’ problems.

The US reported a record 182,832 new coronavirus cases on Thursday, according to the Covid Tracking Project, bringing the total past 11.5m. Hospitalisations reached 80,698, another record.

In recent months, laboratories have pooled samples to test several at once. The method helped relieve strain on testing capacity by allowing labs to carry out individual testing only on the smaller portion of positive samples.

But positive results are now so common, laboratories have decided instead to test every sample individually, causing further delays to results.

Mara Aspinall, a professor of biomedical diagnostics at Arizona State university, said: “We are already seeing increased demand for tests, and producers say they are selling all of the capacity they can produce.”

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“This could lead to delays in the results,” he added. “The problem is that if it is taking 7-10 days, by the time they come back they are simply not relevant.”

Public health officials worry that the spike in demand for tests suggests that millions of Americans are planning to travel over the coming week, in contravention of official advice.

The US Centers for Disease Control and Prevention recommended on Thursday that Americans remain in place for the duration of the Thanksgiving break.

Public health officials are particularly worried that cold weather across much of the country will lead to households mixing indoors. Students also pose a particular threat, given that millions are keen to go home after a disrupted term when many were confined to their halls of residence while taking courses online.

“Whoever has not lived in your household for the 14 days before the celebration should not be considered a member of your household,” said Erin Sauber-Schatz, who leads the CDC’s community intervention work. “For college students coming home for the holidays or military members . . . you definitely need to take extra care.”

CDC officials said people should hold Thanksgiving meals outside if possible, or open windows and wear masks if indoors — even around members of their own family. Dr Sauber-Schatz recommended asking overnight guests to use a separate bathroom from the rest of the household if possible.

But experts worry that the CDC’s strengthened guidance has come too late to change travel plans for much of the country.

“Plans have already been made,” said Barry Bloom, professor of public health at Harvard University.

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US national holidays have already been blamed for fuelling the spread of the virus. The second wave of cases peaked in late July — almost exactly two weeks after Independence Day celebrations. A smaller rise was recorded two weeks after Memorial day in May.

Mr Bloom warned: “We may just begin to see the impact of what happens over Thanksgiving in mid-December — just as people begin travelling all over again for the Christmas break.”

Additional reporting by Peter Wells in New York

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Via Financial Times