Frequent, rapid testing can curb Covid-19 transmission within weeks: Study

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Testing half the population each week with inexpensive and rapid Covid-19 tests can drive the pandemic to elimination within weeks, even though the tests are significantly less sensitive than benchmark clinical diagnoses, according to a new study. The research, published in the journal Science Advances, noted that such a strategy could lead to “personalized home orders” without closing restaurants, bars, retail stores and schools.

Scientists, including those at the University of Colorado at Boulder in the United States, say the sensitivity levels of the different types of Covid-19 tests currently in use around the world vary widely. Antigen testing requires a relatively high viral load – about 1,000 times more virus than PCR testing – to detect infection, they said.

Another test, known as the RT lamp, can detect the virus about 100 times as many viruses as PCR, the study noted. Scientists added that the benchmark PCR test requires only 5,000 to 10,000 copies of the viral genetic material, RNA, per milliliter of sample – meaning it can catch the virus very early or very late.

“Our general conclusion is that in public health, it is better to have a less sensitive test with results today than a more sensitive test with results tomorrow,” said lead author of the study Daniel. Larremore of the University of Colorado at Boulder in the United States.

“Rather than telling everyone to stay home to make sure someone who is sick doesn’t pass it on, we could give orders to stay home only to people with contagious disease so everyone can live their lives. “said Larremore.

In the study, scientists assessed whether the sensitivity, frequency, or time to complete tests are the most important in stopping the spread of Covid-19.

They analyzed the available literature on how the viral load rises and falls inside the body during infection, when people tend to have symptoms, and when they become contagious.

Using mathematical modeling, scientists predicted the impact of screening with different types 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 inhabitants.

They found that when it came to curbing propagation, frequency and turnaround time were much more important than the sensitivity of the tests.

Citing a hypothetical example, the researchers said that in a large city, widespread testing twice a week with a rapid, but less sensitive test reduced the degree of infectivity of the virus by 80%. But twice-weekly testing with a more sensitive PCR test, which takes up to 48 hours to return results, reduced infectivity by just 58%, the study noted. When the amount of testing was the same, he said the rapid test still reduced infectivity better than the slower, more sensitive PCR test.

Indeed, about two-thirds of those infected show no symptoms and, while awaiting their results, continue to spread the virus, the scientists explained. “This article is one of the first to show that we should care less about the sensitivity of tests and, in public health, prioritize frequency and turnaround time,” said Roy Parker, senior author of the study, from the Howard Hughes Medical Institute in the United States.

Researchers believe the results demonstrate the power of frequent testing to shorten the pandemic and save lives.

In one scenario, in which four percent of people in a city were already infected, they said rapid testing of three out of four people every three days reduced the number ultimately infected by 88 percent and was “enough to drive the disease.” epidemic towards extinction in six weeks. “” These rapid tests are contagiousness tests. They are extremely effective at detecting Covid-19 when people are contagious, “said Michael Mina, another co-author of the study. from the Harvard TH Chan School of Public Health in the United States.

Some rapid tests, he added, can return results in 15 minutes while PCR tests can take several days.

“In a matter of weeks, we could see this epidemic go from a huge number of cases to very manageable levels,” Mina said.

Researchers believe it’s time to change the testing strategy for Covid-19, from something available to people with symptoms, to seeing it as a vital tool in breaking the chains of transmission.

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