False negatives of coronavirus tests can reach up to 30 percent, experts think, leading thousands to believe they are virus-free.
A false negative result – when people are wrongly told they don’t have the virus, when in fact they do – would be mainly to blame for incorrect swabbing.
Health professionals are trained to wipe a potentially infected person while home kits come with instructions, but experts say there will be mistakes.
Scientists say it is “ dangerous ” to rely on test results to send pandemic treatment alone, killing at least 34,466 British.
They claim that the symptoms should not be put aside just because a person has a negative result and they should be told to isolate themselves just in case.
It follows warnings to ministers that up to one in four COVID-19 cases will be missed because the list of symptoms is not broad enough.
Heads of health in the UK told the public to watch out for coughs and high temperatures for months.
But by missing sore muscles, loss of taste and smell, and headaches, experts fear that Britain will not be able to control the crisis.
Health professionals are trained to wipe a potentially infected person while home kits come with instructions, but experts say there will be mistakes. Pictured: A health worker takes a cotton swab to test a key worker at Royal Papworth Hospital in Cambridge on May 5, 2020
Nasopharyngeal smears are the preferred test choice for SARS-CoV-2 worldwide because it collects the most concentrated sample. A long, flexible cotton swab should be inserted deep into the nostril and along the ‘floor’ of the nose to collect a slime sample. But the invasive test is so uncomfortable that it has been described as ‘being put into the brain’
According to the Department of Health, nearly 2.5 million tests have been performed in the UK so far, of which 240,161 are positive.
About 40 percent of the tests are repeated tests to find out if someone has removed the virus, for example, when a patient leaves the hospital.
Public Health England has not disclosed how many test results could be incorrect.
But experts believe false negatives are close to 10 to 30 percent.
Lawrence Young, a virologist and infectious disease expert at Warwick University, told MailOnline, “I suspect about 30 percent of the results are false negative.
“That means that for every 100 people you test positive, 30 come out negative.”
Tens of thousands more people are now undergoing Pap smear tests than at the start of the outbreak, as the government increases capacity.
Despite the wave of test numbers, ministers have praised that new cases flatten every day as a sign that the outbreak is on the decline.
But Professor Young asks, “Are we responsible for up to 30 percent of the samples we test that are negative, but actually positive?
Tens of thousands more people are now undergoing Pap smear tests than at the start of the outbreak, as the government increases capacity (see top right). Despite the massive increase in test numbers, ministers have poached that new cases are flattening (bottom right) daily as a sign that the outbreak is decreasing
WHAT IS THE SWAB TEST FOR CORONAVIRUS?
Nasopharyngeal swabs are used to detect respiratory viruses, such as the flu and the new coronavirus.
It is the preferred choice for SARS-CoV-2 testing, according to the Centers for Disease Control and Prevention (CDC).
It involves inserting a long, flexible cotton swab into the nostril and along the nose ‘floor’. This should be done slowly so that it is comfortable.
The goal is to reach the posterior nasopharynx, a cavity consisting of muscles and connective tissue covered with cells and mucus that are similar to the nose. It continues down the throat.
The rod is rotated several times to get enough cells.
The sample is then sent to a laboratory where it is tested to determine if the patient’s cells have been infected with the virus.
The coronavirus is an RNA virus, meaning it uses ribonucleic acid as a genetic material. A process called reverse transcription is needed to transcribe the RNA into readable DNA.
A smear does not collect much RNA at one time, so a polymerase chain reaction (PCR) is used to make billions of copies quickly so that it can be analyzed.
The DNA is dyed in a fluorescent color, which lights up when the coronavirus is present, confirming a diagnosis.
False negatives exist for several reasons, but probably the main reason is a sampling error. It always worries me and many colleagues that there is a problem with the swab and I think mistakes will creep in. ‘
Nasopharyngeal smears are the preferred test choice for SARS-CoV-2 worldwide because it collects the most concentrated sample.
A long, flexible cotton swab should be inserted deep into the nostril and along the ‘floor’ of the nose to collect a slime sample.
The goal is to reach the posterior nasopharynx, a cavity made up of muscles and connective tissue covered with cells and mucus. It continues down the throat.
But the invasive test is so uncomfortable that it has been described as “being put into the brain.” It can cause people to retch and nosebleed.
The alternative is to take two cotton swabs; one from the nostril and another from the back of the throat through the mouth.
This method is used for home test kits – currently some 35,000 are sent per day to key workers and their family members.
Professor Young, who emphasized that nasopharyngeal swabs collect a stronger sample, said he believes there is “ huge variability ” in the way swabs are collected both at home and at drive-through testing facilities in the UK.
“You have to go deep in the nose. If you look at some pictures [of testing facilities]”It won’t happen,” he warned.
“If you’re going to make judgments about one Pap smear, you have to be very careful, especially when you tell people if they can get back to work.”
Paul Hunter, a professor of medicine and scientist in the field of infectious diseases at the University of East Anglia, said that relying on test results is “dangerous.”
Home test kits – of which around 35,000 are currently shipped per day to key workers and their family members – tell people to take two cotton swabs; one from the nostril and another from the back of the throat through the mouth
Professor Young said he believes there is ‘enormous variability’ in the way swabs are collected both at home and at drive-through testing facilities in the UK. Pictured: A drive-in test facility at the Chessington World of Adventures Resort, West London
He told MailOnline, “What I’m concerned about is that if you have symptoms and the test comes back negative, you can go out. That is dangerous because you get many false negatives with the PCR test.
“I think it is dangerous and it will become even more dangerous if the government continues to rely on test results as cases decrease. Because a wrong result can lead to a wider spread, especially if the person is a super spreader.
Professor Hunter said he “believes that both clinical symptoms and the test result are important in assessing risks.”
Likewise, Nick Summerton, an East Yorkshire physician, has expressed concern that people who test negative were not sufficiently warned that they might have the disease.
He told The Sunday Times: “Most days I meet a person who has” stable door “COVID-19 symptoms, but a negative result.
“They often know as well as I do that this must be false negative, but the post-test guidance is pretty useless to help them do this.”
The most common symptoms of the virus are a persistent cough and high temperatures. These are the only signs listed by the NHS and this is what Public Health England emphasizes that a person must have in order to access a test.
Dr. Summerton, who has also served as a government advisor during the pandemic, has urged that symptoms such as fatigue, shortness of breath and loss of appetite be included in the UK’s top symptom list.
He said that the public may be reassured that they do not have the coronavirus when looking at the NHS website, and therefore reluctantly go around to spread it to others.
He warned that the UK will not be able to “get a grip on the epidemic” by ignoring the presence of symptoms previously thought to be unusual, The Sunday Times reported last week.
Compared to adults, children are less likely to have telltale symptoms and may not show any signs of the virus at all. Pictured: About 73 percent of American children have a fever, cough, or shortness of breath, compared to 93 percent of adults
WHAT SYMPTOMS LIST HEALTH INFORMATION? CDC’S PREVIOUS AND CURRENT LIST OF CORONAVIRUS SYMPTOMS
The NHS lists the following as the main symptoms of the coronavirus:
- a high temperature – this means you are hot to touch your chest or back (no need to measure your temperature)
- a new, continuous cough – this means a lot of coughing for more than an hour, or 3 or more coughing attacks in 24 hours (if you usually cough this may be worse than usual)
It also says you should use the NHS 111 service if you have those symptoms
The Centers for Disease Control and Prevention (CDC)
Until recently, the CDC listed only three symptoms of coronavirus on its website:
- Shortness of breath
Last week, the CDC expanded its list to include the following characters:
- Shake repeatedly with chills
- muscle strain
- Sore throat
- New loss of taste or smell
The World Health Organization
Most common symptoms:
- Dry cough
Less common symptoms:
- Aches and pains
- Sore throat
- Loss of taste or smell
- Rash or discoloration of fingers or toe
- Difficulty breathing or shortness of breath
- Chest pain or pressure
- Loss of speech or movement
Ministers have been warned that in a quarter of cases, the virus cannot be detected because it shows symptoms of the virus other than coughing and fever, The Telegraph reports.
Scientists from the new and emerging Respiratory Virus Threat Advisory Group (Nervtag) expressed concern that people with only lesser-known symptoms may not isolate themselves or access a test.
They raised issues at a Nervtag meeting on March 13, the day after Prime Minister Boris Johnson first told the public to isolate themselves if they coughed or developed high temperatures.
According to meeting minutes, John Edmunds, a professor of infectious disease modeling at the London School of Hygiene & Tropical Medicine, pointed out a paper stating that “one in four cases could be skipped if the criteria of only coughing and / or fever were used” .
The minutes of the meeting said, “There was concern that the phraseology might mean that some individuals with the virus may not meet the definition.”
Research has shown a range of symptoms that SARS-CoV-2 can cause in addition to the typical cough and fever. Sometimes these depend on the severity of the disease.
On March 31, researchers at King’s College London said that nearly 60 percent of coronavirus patients experienced loss of taste and smell.
They collected data from over 1.5 million Britons who downloaded the COVID Symptom Tracker app.
About 59 percent of those who reported their health and tested positive on March 29 reported a loss of smell and taste, compared to 18 percent of those who tested negative.
But the government rejected loss of smell and taste – which Health Secretary Matt Hancock said he suffered from during his illness – as “anecdotal evidence” on April 3.
The World Health Organization lists 13 symptoms of COVID-19, and the CDC has bumped up to nine in recent weeks.
Both recognize muscle pain, loss of taste and smell and headache as typical signs of SARS-CoV-2 infection.
Peter Openshaw, a professor of experimental medicine at Imperial College London, who is on Nervtag, said it was important for patients and doctors to broaden their perception of how the coronavirus presents in different people.
He said, “With the self-reported symptoms, the loss of sense of smell emerges as very, very frequent.
But in terms of how often that would actually lead to a diagnosis of COVID, that’s not entirely clear.
“The original, very restrictive definition, I think, was not to pick up many people who may have COVID.”
Professor Openshaw confirmed that one in four cases could still be ‘easily’ missed due to the focus on coughing and high temperatures.
MailOnline has contacted the Department of Health and Public Health England for comment.
Yvonne Doyle, Medical Director of Public Health England: “The UK test system is built on a strong foundation using the latest evidence and expert advice. Many studies are currently underway into the accuracy of the COVID-19 test, and there are a number of different methods available to assess it. However, there is no such thing as a perfect test.
“We have made every effort to make testing as strong as possible according to our high standards.”