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Frequent, rapid testing could cripple COVID-19 within weeks, can curb its spread

Frequent, rapid testing could cripple COVID-19 within weeks, can curb its spread

Last Reviewed : 11/24/2020
Frequent, rapid testing could cripple COVID-19 within weeks, can curb its spread

  • To curb the spread of COVID-19, test frequency and test turnaround-time are far more important than test sensitivity, according to a new study. Frequent, rapid tests make 'personalized stay-at-home orders' possible.
  • We should worry less about test sensitivity and, when it comes to public health, prioritize frequency and turnaround time.

 

Testing half the population weekly with inexpensive, rapid-turnaround COVID-19 tests would drive the virus toward elimination within weeks -- even if those tests are significantly less sensitive than gold-standard clinical tests, according to a new study published today by University of Colorado Boulder and Harvard University researchers.

When it comes to public health, it's better to have a less sensitive test with results today than a more sensitive one with results tomorrow. Rather than telling everyone to stay home so you can be sure that one person who is sick doesn't spread it, we could give only the contagious people stay-at-home orders so everyone else can go about their lives.

They used mathematical modeling to forecast the impact of screening with different kinds of tests on three hypothetical scenarios: in 10,000 individuals; in a university-type setting of 20,000 people; and in a city of 8.4 million.

For instance, in one scenario in a large city, widespread twice-weekly testing with a rapid but less sensitive test reduced the degree of infectiousness, or R0 ("R naught"), of the virus by 80%. But twice-weekly testing with a more sensitive PCR (polymerase chain reaction) test, which takes up to 48 hours to return results, reduced infectiousness by only 58%. When the amount of testing was the same, the rapid test always reduced infectiousness better than the slower, more sensitive PCR test.

That's because about two-thirds of infected people have no symptoms and as they await their results, they continue to spread the virus.

In a city where 4% of its individuals were already infected, rapid testing three out of four people every three days reduced the number ultimately infected by 88% and was "sufficient to drive the epidemic toward extinction within six weeks."

Antigen tests require a relatively high viral load -- about 1,000 times as much virus compared to the PCR test -- to detect an infection. Another test, known as RT-lamp (reverse transcription loop-mediated isothermal amplification), can detect the virus at around 100 times as much virus compared to the PCR. The benchmark PCR test requires as little as 5,000 to 10,000 viral RNA copies per milliliter of sample, meaning it can catch the virus very early or very late.

In the past, federal regulators and the public have been reluctant to embrace rapid tests out of concern that they may miss cases early in infection. But, in reality, an infected person can go from 5,000 particles to 1 million viral RNA copies in 18 to 24 hours, said Parker.

These rapid tests are contagiousness tests and are extremely effective in detecting COVID-19 when people are contagious. Rapid tests can cost as little as $1 each and return results in 15 minutes. Some PCR tests can take several days.

Rapid testing could also be the key to breathing life back into former super spreader threats like football stadiums, concert venues and airports, with patrons testing themselves on the way in and still wearing masks as a precautionary measure, Larremore said.

Less than .1% of the current cost of this virus would enable frequent testing for the whole of the U.S. population for a year.

 

Story Source: University of Colorado at Boulder.

Note: Content may be edited for style and length.

Reference:

  1. Daniel B. Larremore, Bryan Wilder, Evan Lester, Soraya Shehata, James M. Burke, James A. Hay, Milind Tambe, Michael J. Mina, Roy Parker. Test sensitivity is secondary to frequency and turnaround time for COVID-19 screeningScience Advances, Nov. 20, 2020; DOI: 10.1126/sciadv.abd5393

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