2 in 3 early Covid-19 tests show false negative, study shows
Share article:
Share article:

2 in 3 early Covid-19 tests show false negative, study shows

Credit: Belga

Testing people infected with the new coronavirus (Covid-19) too early in the course of the infection is likely to lead to a false-negative test result, a recent study shows.

Johns Hopkins researchers estimated that people that were tested for the virus in the four days after infection were 67% more likely to test negative, even if they had the virus, by reviewing RT-PCR (reverse transcriptase polymerase chain reaction) test data from seven prior studies.

When the average patient began displaying symptoms of the virus, the false-negative rate was 38%.

“A negative test, whether or not a person has symptoms, does not guarantee that they are not infected by the virus,” said Lauren Kucirka, M.D., Ph.D., M.Sc., obstetrics and gynaecology resident at Johns Hopkins Medicine.

The test performed best eight days after infection, which is about three days after symptoms start occurring, according to the report, published on 13 May in Annals of Internal Medicine, one of the most widely cited and influential speciality medical journals in the world.

However, even then, there was a false negative rate of 20%, meaning one in five people who had the virus had a negative test result.

“How we respond to and interpret, a negative test is very important because we place others at risk when we assume the test is perfect,” Kucirka said. “However, those infected with the virus are still able to potentially spread the virus,” she added.

Related News:


Patients who have high-risk exposure should be treated as if they are infected, according to Kucirka, especially if they have symptoms that are consistent with Covid-19.

As shown in tests for other viruses, as well as for the coronavirus, if a swab misses collecting cells infected with the virus, or if virus levels are very low early during the infection, some tests can produce negative results.

In April, Belgian virologist and inter-federal Covid-19 spokesperson Steven Van Gucht already suggested that testing too late could also result in false-negatives, after the Belgian centre for evidence-based medicine published an article stating that approximately 30% of PCR tests result in a false-negative.

However, since these tests are known for their quick results, they have been widely used among high-risk populations such as nursing home residents, hospitalised patients and health care workers.

False-negatives are mainly due to incorrectly swabbing a patient, according to Joris Moonens, spokesperson for the Flemish Agency for Care and Health.

Johns Hopkins Medicine researchers reviewed test data from seven prior studies, covering a combined total of 1,330 respiratory swab samples, from hospitalised patients as well as those identified via contact tracing in an outpatient setting.

“We are using these tests to rule out Covid-19, and basing decisions about what steps we take to prevent onward transmission, such as selection of personal protective equipment for health care workers,” said Kucirka.

“As we develop strategies to reopen services, businesses and other venues that rely on testing and contact tracing, it is important to understand the limitations of these tests,” she added.

Ongoing efforts to improve tests and better understand their performance in a variety of contexts will be critical as more people are infected with the virus and more testing is required.

The sooner people can be accurately tested and isolated from others, the better we can control the spread of the virus, the researchers say.

Maïthé Chini
The Brussels Times

Latest news

Covid-19 decisions made ‘too hastily’, socialist leader argues
The government is missing a "general lack of method" when it comes to how coronavirus fighting measures are decided on, according to the leader of ...
Aggression against railway staff more than doubled since 2020
In the first three quarters of 2021, the number of reports of aggression against national railway company SNCB's staff has more than doubled compared ...
Intervention hotline 1722 activated following bad weather warnings
Following bad weather warnings from Belgium's Royal Meteorological Institute of Belgium (RMI), the Federal Public Service (FPS) Home Affairs has ...
Several rush hour train services to be scrapped from Monday
Up to ten peak time trains to and from Brussels will be temporarily cancelled starting from Monday, Belgian railway company SNCB announced this ...
Thousands march in Brussels to raise awareness of violence against women
More than 3,000 people took to the streets of Brussels on Sunday afternoon for a national march to raise awareness of violence against women in ...
Efficacy of vaccines against new variant known in a few weeks, virologist says
The efficacy of the current coronavirus vaccines against the new Omicron variant will be clear in one to two weeks, Belgian virologist Marc Van Ranst ...
Scientists could have communicated better during pandemic, survey shows
The majority of Flemish people continue to trust scientists, however, only half of them feel scientists communicated understandably during the ...
Closing borders and new travel restrictions: Countries react to Omicron variant
As more cases of the new Omicron variant of the coronavirus are being reported across the world, more and more countries are imposing tougher travel ...
Europe’s largest vintage clothes store is in Ghent this weekend
Europe's largest pop-up store for second-hand clothes is once again setting up shop in Ghent on Sunday, offering more than five tonnes of vintage ...
Animal welfare in EU’s pork sector: What’s wrong?
EU has put into place legislation to ensure that animal welfare conditions are respected in its agricultural policy but the breaches of its ...
‘Not feasible’: Doctors refuse to follow new testing strategy
Doctors have warned they will not follow the government's adapted testing strategy which would see vaccinated people who were in close contact with a ...
Flanders introduces ‘invisible’ speed cameras
New digital speed cameras that are essentially invisible to the road user are being introduced on various roads and motorways in Flanders, Flemish ...