Researchers at Johns Hopkins University in the US have found that testing people for Covid-19 too soon will likely produce “false negative” results, even though they might eventually be tested positive for the virus. Also read – Langar in the Middle #BlackLivesMatter Protest: Sikh Community in New York Make Sure Protesters Don’t Sleep on Empty Stomach
“A negative test, whether a person has symptoms or not, does not guarantee that they are not infected by the virus,” study researcher Lauren Kucirka of JHU said in a paper published in the journal Annals of Internal Medicine. Also read – Malaika Arora Building Sealed by BMC After Resident Tests Coronavirus-Positive
“How we respond and interpret negative tests is very important because we put others at risk when we think the test is perfect,” Kucirka added. Also read – Anti-Virus Cloth to Combat Coronavirus? Gujarat Company Comes With Long-term Solution Amid the COVID-19 Pandemic
According to the researchers, one of several ways to assess the presence of SARS-CoV-2 infection is a method called transcription-polymerase back chain reaction (RT-PCR).
These tests quickly make copies and detect the genetic material of the virus. However, as shown in tests for other viruses such as influenza, if cotton does not collect virus-infected cells, or if the virus level is very low at the start of infection, some RT-PCR tests can produce negative results.
Because the tests return relatively fast results, they have been widely used among high-risk populations such as nursing home residents, hospitalized patients and health care workers.
Previous studies have shown or suggested false negatives in this population.
For the new analysis, the research team reviewed RT-PCR test data from seven previous studies, including two pre-printed and five peer-reviewed articles. The study included a combined total of 1,330 respiratory swab samples from various subjects including patients who were hospitalized and those identified through contact tracing in outpatient settings.
From this data, the researchers calculated the daily false negative rates, and have made statistical codes and data publicly available so the results can be updated as more data is published.
The researchers estimated that those who were tested with SARS-CoV-2 within four days after infection were 67 percent more likely to be tested negative, even if they had the virus.
When the average patient starts showing viral symptoms, the false negative number is 38 percent. This test shows the best performance eight days after infection but even has a false negative rate of 20 percent, which means one in five people who have the virus have a negative test result.
According to the researchers, ongoing efforts to improve tests and better understand their performance in various contexts will be important because more people are infected with the virus and more testing is needed.
“The faster people can be accurately tested and isolated from others, the better we can control the spread of the virus,” the authors wrote.
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