New 'hypersensitive' rapid test can tell whether patients have Covid or flu


A new test developed by researchers at UC Santa Cruz looks for both the coronavirus and the flu, with an accuracy level comparable to gold-standard COVID tests.

The test uses a fluorescent probe to search for antigens – proteins on the surface of a virus molecule – which may belong to either disease.

Since COVID and flu have similar symptoms, a fast yet highly accurate test like this will help quickly rule out one infection and potentially confirm the other so that patients only have to endure one of the unpleasant screenings. 

And from a public health perspective, confirmation that someone has flu, coupled with a negative test for Covid will offer confidence that the person positive for flu doesn’t need to quarantine, or be contact traced to prevent an outbreak. 

The novel technology developed for this test may also be adapted in the future to test simultaneously for other diseases. 

A new test developed by researchers at UC Santa Cruz looks for both the coronavirus and the flu, with an accuracy level comparable to gold-standard COVID tests

A new test developed by researchers at UC Santa Cruz looks for both the coronavirus and the flu, with an accuracy level comparable to gold-standard COVID tests

Testing has been one of the most challenging aspects of the pandemic, as researchers and medical professionals alike struggle to determine how many people are actually infected with the coronavirus.

And while lines of thousands of cars snaked away from drive-in testing sites during the fall and holiday surges of COVID-19 in the U.S., the prospect of getting a ‘brain scraper’ test for Covid is hardly appealing. 

Currently if someone who tests negative for Covid wants to know if their symptoms are due to flu, they’ll have to go through a similar test again. 

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According to data from the Centers for Disease Control and Prevention (CDC), flu all but disappeared this past season amid the coronavirus pandemic.  

Stepped-up hand-washing, masking and people generally staying away from one another amid the pandemic was likely responsible for a dramatic reduction in the transmission of flu. 

But experts also suspect that this year’s flu cases are an undercount because many Americans skipped care generally amid fears of contracting COVID-19, or didn’t follow up with flu diagnostics after testing negative for coronavirus. 

The polymerase chain reaction (PCR) test for either Covid or flu, commonly accepted as the ‘gold standard,’ is highly accurate. 

But it can take days for patients to receive their results, and the test is expensive- making it challenging to use on a broad scale.

Antigen tests have steadily become more popular as a faster, cheaper alternative to PCR. While a PCR test searches for specific genetic material that matches the coronavirus, an antigen test looks for a protein on the surface of that virus.

These tests are also commonly called ‘rapid tests’ because they can give patients a result in fifteen minutes. Such a short time frame makes it easy for patients to act upon their result.

But the widely-used antigen tests are not as accurate as PCR. They have a higher rate of false negatives, meaning that someone who receives a negative result on an antigen test is more likely to actually be infected with the coronavirus, compared to someone who receives a negative result on a PCR test.

A new antigen test from researchers at University of California Santa Cruz addresses this accuracy issue and broadens the test’s utility by looking for the coronavirus and a common flu virus at the same time.

The test uses two biomarkers to identify a sample as coronavirus or influenza. If the patient has COVID, the test lights up green, and if they have the flu, it lights up red.

The test uses two biomarkers to identify a sample as coronavirus or influenza. If the patient has COVID, the test lights up green, and if they have the flu, it lights up red.

Like other antigen and PCR tests, the UC Santa Cruz test starts with a nose swab. This sample is then examined with a fluorescent reporter probe: a piece of genetic material that will ‘light up’ with fluorescence if it identifies a specific virus.

For this test, the UC Santa Cruz researchers developed a new molecule coded to look for a coronavirus antigen and a flu virus antigen at the same time.

This special molecule shines brightly enough that someone administering a test can see it without any extra equipment. And the genetic material doesn’t need to be amplified (copied over and over), so this test may provide results quickly like other antigen tests.

At the same time, since this fluorescent molecule is linked specifically to coronavirus and flu proteins, it can identify these viruses with a higher degree of accuracy than other antigen tests. For this reason, the researchers call their test ‘ultrasensitive.’

The test also has special, colored markers to distinguish between the two viruses. If coronavirus is present, the test will show a green mark, and if influenza is present, the test will show a red mark.

Novel tests help U.S. experts keep track of where the coronavirus is spreading.

Novel tests help U.S. experts keep track of where the coronavirus is spreading.

This ability to distinguish between two common viruses may be especially useful during flu season.

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COVID and the flu share similar symptoms. The CDC lists ten that are common to both diseases: fever, cough, shortness of breath, fatigue, sore throat, runny nose, muscle pain, headache, vomiting, and diarrhea.

While the 2020-2021 flu season has been mild in the U.S., past flu seasons have sent hundreds of thousands of Americans to the hospital. The 2017-2018 flu season, which was particularly harsh, killed an estimated 61,000.

Using a test like this one could help doctors quickly diagnose patients who come in with any of the common flu/COVID symptoms. The test may be useful in both hospitals and outpatient clinics.

The UC Santa Cruz test would also have great utility as an over-the-counter product. Some rapid antigen tests are now available at pharmacy chains, without any doctor’s note- imagine if you could go to your local CVS and pick up a test that can tell you, in 15 minutes, if you have COVID or the flu.

This fluorescent technology may be useful for detecting other viruses as well. In fact, the researchers were originally developing this technology for Zika virus when the pandemic hit.

‘Once we were allowed to come back to the lab for essential research, my students started coming in to work in the lab by themselves on a coronavirus test,’ said senior author Holger Schmidt in a press release. ‘It was a heroic effort by my students to develop these tests from scratch. First we were shut down by the pandemic, and then the wildfires hit and we had to evacuate our samples to Stanford and shut down again. But they kept going.’ 



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