Almost a third of the negative coronavirus test results could be false, scientists say, leaving thousands of people to believe they are virus-free.
People who are wrongly says they do not have the virus when in fact – called a “false negative” – they could spread the disease if they think they can return to work safely.
The false negative results are mainly due to an incorrect swab, experts say. Health leaders have also admitted that the test itself, called the PCR test, is “not perfect.”
Health workers are trained to swab a potentially infected person, while home kits come with instructions – but experts say there are bound to be mistakes.
Scientists say it is “dangerous” to rely on test results to direct management only of the pandemic, in which at least 34,466 Britons died.
They argue that symptoms should not be ruled out simply because a person has a negative result and that they should be told to isolate themselves just in case.
It follows warnings to ministers that up to one in four cases of COVID-19 will be missed because the list of symptoms is not wide enough.
Heads of health in the UK have told the public to watch out for coughs and high temperatures for months.
But forgetting about sore muscles, loss of taste and odor and headaches, experts fear that Britain will not be able to contain the crisis.
Health workers are trained to swab a potentially infected person, while home kits come with instructions – but experts say there are bound to be mistakes. Pictured: a health worker takes a swab to test a key worker at the Royal Papworth Hospital in Cambridge on May 5, 2020
Nasopharyngeal swabs are the preferred choice of tests for SARS-CoV-2 worldwide because they collect the most concentrated sample. A long, soft cotton is supposed to be inserted deep into the nostril and along the “floor” of the nose to collect a sample of mucus. But the invasive test is so uncomfortable that it has been described as “being stabbed in the brain”
So far, nearly 2.5 million tests have been done across the UK, according to the Department of Health, of which 240,161 have been positive.
Some 40% of the tests have been repeated to clarify if someone has gotten rid of the virus, such as when a patient leaves the hospital.
Public Health England has not disclosed the number of test results that could be incorrect.
But experts estimate that false negatives are in the range of 10-30%.
Lawrence Young, virologist and infectious disease specialist at the University of Warwick, told MailOnline: “I guess about 30% of the results are a false negative.
“This means that for every 100 people tested positive, 30 will be negative.”
Tens of thousands more are currently undergoing swab tests than at the start of the epidemic as the government increases its capacity.
Despite the large increase in the number of tests, the ministers boasted that the new daily cases are stabilizing, a sign that the outbreak is slowing down.
But Professor Young asks, “Do we represent up to 30% of the samples we test which is negative is actually positive?
Tens of thousands more are currently undergoing swab tests than at the start of the epidemic as the government increases its capacity (see top right). Despite the sharp increase in the number of tests, the ministers boasted that the new daily cases are stabilizing (bottom right), a sign that the outbreak is slowing down
WHAT IS THE CORONAVIRUS ROD TEST?
Nasopharyngeal swabs are used to detect respiratory viruses, such as the flu and the new coronavirus.
It is the preferred choice for screening for SARS-CoV-2, according to the Centers for Disease Control and Prevention (CDC).
This involves inserting a long, soft cotton pad into the nostril and along the “floor” of the nose. This is supposed to be done slowly so that it is comfortable.
The goal is to reach the posterior nasopharynx, a cavity made up of muscles and connective tissue, covered with cells and mucous membranes similar to the nose. It continues down the throat.
The swab is rotated several times to obtain enough cells.
The sample is then sent to a laboratory, where it will be tested to determine if the patient’s cells are infected with the virus.
The coronavirus is an RNA virus, which means it uses ribonucleic acid as genetic material. A process called reverse transcription is necessary to transcribe RNA into readable DNA.
A swab sample doesn’t collect a lot of RNA at one time, so a polymerase chain reaction (PCR) is used to make billions of copies quickly so it can be analyzed.
The DNA is stained with a fluorescent color, which shines if the coronavirus is present, confirming a diagnosis.
“False negatives are due to several reasons, but the main reason is probably a sampling error. This still worries me and many colleagues have a problem with the swab and I think some mistakes will creep in.
Nasopharyngeal swabs are the preferred choice of tests for SARS-CoV-2 worldwide because they collect the most concentrated sample.
A long, soft cotton is supposed to be inserted deep into the nostril and along the “floor” of the nose to collect a sample of mucus.
The goal is to reach the posterior nasopharynx, a cavity made up of muscles and connective tissue, covered with cells and mucous membranes. It continues down the throat.
But the invasive test is so uncomfortable that it has been described as “being stabbed in the brain.” This can cause nausea and nosebleeds.
The alternative is to take two swabs; one from the nostril and one from the back of the throat through the mouth.
Home test kits – of which approximately 35,000 are currently sent daily to key workers and their household members – use this method.
Studies conducted at the start of the epidemic in China have suggested that test results vary depending on the type and day when the swab is taken during the illness.
A study, published on MedRxiv, found that nasal swabs correctly identified only 73% of severe COVID-19 cases and 72% of mild cases during the first week of symptoms.
The positive rate of throat swabs was even lower, around 60%. When throat swabs were taken more than eight days after symptoms, the positive rate fell to 50% in severe cases and to 29.6% in mild cases.
Eight days may seem like a long wait for a test. But in the UK, access to tests has proven difficult. Home test kits and slot machines in establishments can be sold online in minutes.
Professor Young, who pointed out that the nasopharyngeal swabs collect a stronger sample, said he thought there was “enormous variability” in how the swabs are collected, both at home and in screening facilities in the UK.
“You have to go deep into your nose. When we look at some photos [of testing facilities], that does not happen, “he warned.
“If you’re going to pass judgment on a sample test, you have to be very careful, especially if you tell people if they can go back to work.”
Paul Hunter, professor of medicine and infectious disease scientist at the University of East Anglia, said relying on test results was “dangerous.”
Home test kits – about 35,000 of which are currently sent daily to key workers and their household members – instruct people to take two tampons; one from the nostril and another from the back of the throat through the mouth
Professor Young said he believed there was “enormous variability” in the way swabs are collected, both at home and at drive-through testing facilities across the UK. In the photo: a test rig behind the wheel of the Chessington World of Adventures Resort, west of London
He told MailOnline, “What worries me is that if you have symptoms and the test is negative, you can go out. This is dangerous because you get a lot of false negatives with the PCR test.
“I think it’s dangerous, and it will become even more dangerous, if the government continues to rely on test results as cases decrease. Because a bad result could lead to wider spread, especially if the person is a super spreader.
Professor Hunter said he “believes the clinical symptoms and the test result are important in assessing the risk.”
Likewise, Nick Summerton, a general practitioner in East Yorkshire, expressed concern that people who tested negative were not given enough warning that they might have the disease.
He told the Sunday Times, “Most of the time, I meet a person who has COVID-19” barn door “symptoms but a negative result.
“They often know as well as I do that it must be a false negative, but the post-test advice is not really helpful in helping them. “
The most common symptoms of the virus are a persistent cough and high temperature. These are the only signs listed by the NHS and this is what Public Health England insists that a person must have to access a test.
Dr. Summerton, who also acted as government adviser during the pandemic, requested that symptoms such as fatigue, shortness of breath and loss of appetite be included in the list of main symptoms for Great Britain .
He said the public could be reassured not to have the coronavirus if they visited the NHS website, and therefore reluctantly disseminate it.
He warned that the United Kingdom would not be able to “control the epidemic” by ignoring the presence of symptoms that previously could be considered unusual, the Sunday Times reported last week.
Compared to adults, children are less likely to have tell-tale symptoms and may not show any signs of the virus. Pictured: About 73% of American children have a fever, cough, or shortness of breath, compared to 93% of adults.
WHAT SYMPTOMS ARE THE LIST OF HEALTH OFFICIALS? PREVIOUS AND CURRENT LIST OF THE CORONAVIRUS SYMPTOMS CDC
The NHS lists the following as the main symptoms of coronavirus:
- high temperature – this means you feel hot to the touch on your chest or back (you don’t need to measure your temperature)
- a continuous new cough – this means coughing a lot for more than an hour, or 3 or more coughing episodes in 24 hours (if you usually have a cough, it may be worse than usual)
It also says to use the NHS 111 service if you have these symptoms
The Centers for Disease Control and Prevention (CDC)
Until recently, the CDC listed only three symptoms of coronavirus on its website:
Last week, the CDC expanded its list to include the following signs:
- Repeated shaking with chills
- Muscle pain
- Irritated throat
- New loss of taste or odor
The World Health Organization
The most common symptoms:
- Dry cough
Less common symptoms:
- Aches and pains
- Irritated throat
- Loss of taste or odor
- Rash or discoloration of the fingers or toes
- Difficulty breathing or shortness of breath
- Chest pain or pressure
- Loss of speech or movement
Ministers have been warned that the virus may go undetected in a quarter of the cases because they have symptoms of the virus other than cough and fever, reports The Telegraph.
Scientists at the Advisory Group on Threats to New and Emerging Respiratory Viruses (Nervtag) have expressed concern that people with only lesser-known symptoms do not isolate themselves or have access to a test.
They raised questions at a Nervtag meeting on March 13, the day after Prime Minister Boris Johnson told the public to isolate himself if he developed a cough or high temperature.
According to the minutes of the meeting, John Edmunds, professor of infectious disease modeling at the London School of Hygiene & Tropical Medicine, pointed to a document that said that one in four cases could be missed if the criteria for only a cough and / or fever is used ‘.
The minutes of the meeting stated: “There was concern that the phraseology could mean that a number of individuals with the virus might not meet the definition. “
Research has shown a range of symptoms that SARS-CoV-2 can cause beyond the typical cough and fever. Sometimes it depends on the severity of the disease.
On March 31, researchers at King’s College London reported that almost 60% of coronavirus patients had lost their taste and odor.
They collected data from more than 1.5 million Britons who downloaded the COVID Symptom Tracker app.
Some 59% of those who reported being in good health as of March 29 and found positive reported loss of smell and taste, compared with 18% of those who tested negative.
But the government has dismissed the loss of smell and taste – which Health Secretary Matt Hancock said he suffered during his illness – as “anecdotal evidence” on April 3.
The World Health Organization has listed 13 symptoms of COVID-19 and the CDC has increased to nine in the past few weeks.
The two recognize that muscle pain, loss of taste and odor, and headache are typical signs of SARS-CoV-2 infection.
Peter Openshaw, professor of experimental medicine at Nervtag’s Imperial College London, said it was important for patients and doctors to broaden their perception of how the coronavirus looks in different people.
He said, “In self-reported symptoms, loss of smell appears to be very, very common.
“But as to how often this would actually lead to a diagnosis of COVID, it is not entirely clear.
“The original definition, very restrictive, I think, did not capture many people who could actually have COVID. “
Professor Openshaw confirmed that one in four cases could still be “easily” missed due to the emphasis on coughing and high temperatures.
MailOnline has contacted the UK Department of Health and Public Health for comments.
Yvonne Doyle, medical director of Public Health England, said: “The UK testing system is built on a solid foundation using the latest evidence and expert advice. Many studies are currently underway on the accuracy of the COVID-19 test and a number of different methods are available to assess this. However, there is no perfect test.
“We have worked to make the tests as robust as possible in accordance with our high standards.”