Why Is The Saliva Test Less Sensitive
Saliva is a complex mix of fluids containing water, electrolytes, proteins and enzymes and all of these dilute the viral genetic material of COVID-19.
“The other thing is, saliva is where the virus ends up before it’s transmitted, it’s not where it’s growing, it’s not as direct a test of infection,” Professor Turner says.
What Do The Experts Think
The benefits of saliva testing far outweigh the disadvantages, Professor Turner says.
Dr Mackay agrees and wants to assure people there is no need to have any hesitations about taking a saliva test.
He says rolling out saliva testing in the outbreak hotspots was wise and it has the added benefit of giving researchers more data to examine.
“We’re in this great position where we don’t have a lot of cases so we don’t have the same urgency. We can afford to do things like this and expand the knowledge and that can be leveraged by other places around the world as well.”
Director of the Doherty Institute Sharon Lewin says it would be a “perfect outcome” if people no longer had to leave their home for a COVID-19 test.
The Doherty says there will be ongoing analysis of the saliva testing in Melbourne and further research will “hopefully” be published.
NSW has not ruled out introducing the saliva test if the need arises for greater testing in the future.
What To Do After The Test
Effective 7 February 2022, the government asks you to do your own Covid-19 self-test kit at home. If youre positive and asymptomatic or in category 2A with no comorbidities, you dont need to go to the nearby Covid-19 Assessment Centre . Instead, self-quarantine at home and update your MySejahtera.
However, if youre positive and the symptoms persist, , you should go to the nearby CAC for an RT-PCR test or further action.
Whether youre positive or negative, you should update your MySejahtera status. If the RTK-Ag test is invalid, there might be other external factors that affected the test and it should be done again.
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Findings Build On Collaborative Effort To Design 3d
BOSTONAs the highly transmissible Delta variant of the virus that causes COVID-19 surges in the United States and around the world, rapid and accessible COVID-19 testing and increased vaccination are key to managing the virus spread. Nasopharyngeal swabs long, medical-grade probes used to collect samples from deep in patients noses and throats are the gold standard for COVID-19 diagnostic testing. However, memory of shortages of both the specialized NP swabs during the early days of the pandemic as well as pressure on the trained medical personnel needed to perform the tests point to the need for simpler COVID-19 testing.
In a real-world trial, a team of clinician-researchers at Beth Israel Deaconess Medical Center have demonstrated that tests of self-collected saliva provided comparable results to tests performed by trained healthcare professionals using NP swabs. The researchers concluded that saliva tests detect 93 percent of COVID-19 infections in an outpatient setting. The findings, which are published in the journal Microbiology Spectrum, could help alleviate the testing bottlenecks that have constrained COVID-19 testing since early in the pandemic.
We have demonstrated that for practical purposes, saliva is comparable to NP swabs for COVID-19 testing in outpatient settings, said Arnaout, who is also associate professor of pathology at Harvard Medical School.
Will Any Of The Tests Tell Me Which Variant I Have
None of the COVID-19 tests you take, either at home or at a pharmacy, will tell you if you have a variant, such as Delta. Detecting variants requires genetic testing done in a lab. Across the country, a selection of positive COVID-19 samples are sent to specialized labs, where they are anonymously sequenced to identify variants so that public health officials can monitor COVID-19 trends.
And not all positive specimens are tested only sample amounts are taken. So, if you hear that 75% of cases in an area are a particular variant, for example, that reflects a computation based on the number of samples testedand it is just an estimate.
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South African Study Suggests Nasal Swabs Aren’t The Best Way
byJohn Gever, Contributing Writer, MedPage Today December 27, 2021
If confirmed in follow-up research and if the diagnostics industry can pivot quickly enough, findings from a South African study could make COVID-19 testing a lot easier for patients and healthcare workers, as the SARS-CoV-2 Omicron variant becomes the dominant source of infection.
In a manuscript posted to the medRxiv preprint server on Friday, researchers from the University of Cape Town reported that saliva samples yielded more accurate results in PCR analyses when Omicron was involved compared with those collected via nasal swabs.
When patients carried the Delta variant, on the other hand, nasal swabs were more accurate, according to the group, led by Diana Hardie, MBChB, MMedPath, who also heads the diagnostic virology laboratory at Groote Schuur Hospital.
The findings came from an analysis of 382 patients tested at Groote Schuur from August through this month, with viral whole-genome sequencing performed on isolates from those with positive results. Just over 300 were tested prior to Omicron’s emergence, with 31 testing positive for the Delta variant. Another 74 arrived at the hospital after Omicron became common, of whom 36 were positive for that variant.
All patients had both saliva and mid-turbinate nasal samples taken for RT-PCR analysis. The “gold standard” for positivity in the study was detection of SARS-CoV-2 RNA with either swab.
Safe And Comfortable For Routine Collection
Swabs are notoriously uncomfortable and induce sneezing/coughing due to the invasive nature of collection, which causes further viral spread and puts healthcare workers and the surrounding public in danger. Deep nasal swabs are not ideal for routine testing, and the disagreeability of swabs can be a hurdle to COVID testing, especially for pain-averse populations.
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How Accurate Is The Saliva Test
TLDR: Nasal and throat swabbing remains the gold standard of testing, but a saliva test is better than nothing.
The Peter Doherty Institute for Infection and Immunity in Melbourne put saliva samples to the test in March and April, using specimens from hundreds of patients at the COVID-19 screening clinic at the Royal Melbourne Hospital.
Nasal/throat swabs returned 39 positive results, while the saliva samples returned 33.
The institute says the saliva test has a sensitivity of around 87 per cent in other words, if you ‘spit test’ 100 people who all have COVID-19, about 13 will be false negatives.
A sensitivity rating basically tells us how few viral particles the test needs to pick up to give a positive result.
Microbiology professor Stephen Turner from Monash University has this to say about the “threshold of detection”:
“So you need a certain amount of virus in a sample to get a signal. With a swab test, the amount of virus you need is a lot lower, so it’s more sensitive.
“Whereas with saliva, you need a lot more virus to get a signal.”
It’s impossible to give a definitive sensitivity rating for the nasal/throat swab but it’s more than 90 per cent, Professor Turner says.
Swab tests still produce what Dr Norman Swan calls a “significant minority” of false negatives, with one report by the Johns Hopkins University in the US suggesting the chance could be greater than one in five.
Chances Of A Rapid Test Giving A False Negative
A examined the results of 64 test accuracy studies evaluating commercially produced rapid antigen or molecular tests.
The researchers found that the accuracy of the tests varied considerably. Heres a look at their findings.
Accuracy for people with COVID-19 symptoms
For people with symptoms of COVID-19, the tests correctly gave a positive result an average of 72 percent of the time. The 95 percent confidence intervals were 63.7 to 79 percent, meaning that the researchers were 95 percent confident that the average fell between these two values.
Accuracy for people without COVID-19 symptoms
The researchers found that people without COVID-19 symptoms correctly tested positive in 58.1 percent of rapid tests. The 95 percent confidence intervals were 40.2 to 74.1 percent.
Accuracy during the first week of symptoms versus the second
Rapid tests more accurately provided a positive COVID-19 result when administered during the first week of symptoms. The researchers found that rapid tests correctly identified COVID-19 in an average of 78.3 percent of cases during the first week.
In the second week, the average dropped to 51 percent.
Differences between brands
The researchers found a large range of accuracies between manufacturers of the tests.
Coris Bioconcept scored the poorest and correctly provided a positive COVID-19 result in only 34.1 percent of cases. SD Biosensor STANDARD Q had the highest score and correctly identified a positive COVID-19 result in 88.1 percent of people.
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How Accurate Are At
At-home tests are performed at home, and anyone can use them, regardless of their symptoms or vaccination status. At-home COVID-19 tests are generally approved for use in people over the age of 2.
The testing options include self-collection kits or completely self-administered tests.
Self-collection kits require specimens to be sent to a laboratory, and results return one to two days later. In contrast, the results of a completely self-administered test are available within 1530 minutes. This is an important distinction for someone seeking a quick result.
The two at-home tests are the rapid antigen and molecular nucleic acid tests . The rapid antigen tests look for viral proteins in the body, whereas the molecular PCR tests look for viral genetic material. Both can determine whether someone has an active COVID-19 infection.
Characteristics Of Study Settings
The initial search of the databases identified 49 studies . The titles and abstracts were assessed independently and in duplicate by two review authors . As a result, the full-texts of 20 studies were retrieved for detailed assessment. A total of 4 studies were excluded, and 16 studies were included in the present review . The hand searching did not identify any additional studies. All studies were published in English and all together they included 2928 paired samples.
|Aita et al.,|
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Are Nasal Swab Covid
Some people find the RTK saliva test kit inaccurate, some say were all testing wrongly.
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Currently, with rising cases of Covid-19, we ourselves are worried if we may or may not be having Covid-19.
Asymptomatic cases which are positive cases but without any symptoms are possible and quite a lot. Nowadays, categories 1 and category 2 make up around 99% of the daily Covid-19 cases and categories 3,4,5 make up around less than 1% of the total cases. Check out if you have category 1 or 2 symptoms here.
Hence, if youre feeling a little bit under the weather, youre a close contact or you just wanted reassurance just as a precaution, self-test kits are important to detect Covid-19. The PCR tests are done by professionals. Do note that you dont have to get the PCR test if youre positive and below 60 years old without comorbidities in categories 1 and 2A.
But the issue here lies in which Covid-19 self-test kits should you rely on? As of 11 February 2022, there are 123 products made by companies that are approved for Conditional Approval by the Medical Device Authority .
The RTK-Ag self-test kits are either saliva or nasal swab sample type. Theres also an option for both sample types to be tested in one test tube to increase the detection rate.
Collection Kits Vs Self
Self-collection at-home kits are usually molecular PCR tests that are more accurate than rapid antigen at-home tests.
Generally, molecular PCR COVID-19 tests are more accurate than rapid antigen tests, whether performed in a hospital or at home.
One of the most important factors in getting an accurate result from at-home COVID-19 tests is the amount of virus in your body. If a lot of virus has built up in your body, you are more likely to accurately test positive.
The amount of virus in the body is determined by how long its been since you contracted the virus and whether you have COVID-19 symptoms. If you contracted the virus within one day, you will not have as much virus in your body compared to if you contracted the virus several days ago. Additionally, if a lot of virus has built up in your body, you are more likely to have symptoms.
If you test when you don’t have symptoms, there’s a greater chance of a false-negative result. A false negative is when the test indicates you do not have the disease, but you actually do. In general, when a person is infected with COVID-19, molecular PCR tests can accurately detect the virus 99% of the time. This is called the sensitivity of the test. The sensitivity of rapid antigen tests is lower, at 90%.
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The Demand For Saliva Tests
Collecting a saliva specimen isnt invasive, the samples are reliable, and they keep at room temperature. For all of these reasons, saliva testing options can help overcome some challenges of the pandemic, Wyllie says.
People can quickly and easily collect their own samples and drop them off for testing, she explains. This decreases collection costs and decreases the time required to collect samples.
Early on in the pandemic, people who needed to get tested for SARS-CoV-2 often had to wait in long lines before getting the dreaded nasopharyngeal swabthat is if they were even able to get tested at all.
That was the first thing that was available, Vian Nguyen, MD, national medical director for Wellness 4 Humanity, a company that provides COVID-19 testing kits, tells Verywell. But in addition to that, it was scarce. There was very limited supply of this type of testing.
Scarce resources of nasopharyngeal swabs has not been the only driver for a different test type. Patients have also been pushing for a better way. Lian Nguyen Pham, CEO and co-founder of Wellness 4 Humanity, tells Verywell that the company originally used its saliva test in clinical settings. We saw that everybody actually wanted to request that versus the nasopharyngeal swab, she says. It was more popular in the elderly and also kids. Its just more versatile, and the self-collection is huge.
Early Research On Salivadirect Is Promising
The researchers have already been able to validate results of SalivaDirect on different equipment and with easy-to-find reagents. This flexibility enables continued testing if some vendors encounter supply chain issues, as experienced early in the pandemic, Grubaugh says.
Results so far have found that SalivaDirect is highly sensitive and yields similar outcomes to NP swabbing. However, larger studies are needed to confirm that, Wyllie explains.
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Clinically Relevant Issues Of Covid
Just like the concerns from public health experts for any of the pandemic, two issues of diagnostic testing worth further consideration. In addition to the criteria of who needs to be tested, an important issue relates to the diagnostics itself. Specifically, for RT-PCR, while a positive test result certainly identifies the presence of virus, a negative result may not necessarily rule out SARS-CoV-2 infection. The potential false-negative result could be caused by low virus loads, improper sampling sites and timings, poor technique, and even mutations of viral genome. About the clinical sampling, the US Centers for Disease Control and Prevention guideline recommends collecting upper respiratory specimen for asymptomatic patients. For patients who develop a productive cough, sputum can be used for SARS-CoV-2 testing, although the induction of sputum is not recommended. However, nasopharyngeal swab sampling is technically challenging, requires healthcare professionals, and may impose risk for aerosol generation. These drawbacks thus necessitate the implementation of additional diagnostic approach.
Could It Give A False Positive Result
The Doherty Institute says there is no chance a saliva test could return a positive result if the person is COVID-19 negative.
The institute’s researchers tested saliva specimens from 50 patients who returned negative nasal/throat swabs.
The saliva tests didn’t return any false positives, and in fact, picked up one positive result that the swab testing had missed.
The researchers said this might reflect the inconsistencies that can arise when a swab isn’t taken properly by a nurse or doctor.
“If the result is positive we can trust the saliva test. But if it comes back negative and there’s still some clinical suspicion that that person might have been exposed to the virus, they may then choose to get a nasal swab,” University of Queensland virologist Ian Mackay says.
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Key Findings Of The Study
In the first phase, 28.3 per cent of NPS, saliva, or both samples were positive for SARS-CoV-2. When compared to NPS, the detection rate in saliva was lower . In Phase II, 50.2 per cent of saliva, NPS, or both samples were positive for SARS-CoV-2. When compared to NPS samples, the detection rate in saliva was greater . The detection rate for the 85 saliva samples tested with both procedures was 100% for samples tested with SalivaAll and 36.7 per cent for those tested with procedure U.
What The Research Says
Wyllie and her colleagues at Yale conducted some early research in the spring, now published in the New England Journal of Medicine, comparing nasopharyngeal swabs with saliva samples. Weand othershave seen high concordance between saliva and swabs, Wyllie says.
The Yale study involved 70 hospitalized patients with COVID-19 confirmed with a nasopharyngeal swab at the time of admittance. The researchers later had the patients collect their own saliva samples. At the same juncture, healthcare workers also collected a nasopharyngeal swab from those same patients.
The researchers detected more copies of SARS-CoV-2 RNA, the genetic material of the virus, in the saliva samples than in the nasopharyngeal specimens. And a higher percentage of saliva samples, when compared to nasopharyngeal samples, tested positive for up to 10 days after diagnosis. For example, between one and five days after the patients were diagnosed with COVID-19, 81% of the saliva samples tested positive for the virus, whereas 71% of the nasopharyngeal sampless did.
To test for sample stability, specimens were stored in a transport cooler at room temperature, and showed no significant difference in virus concentration at time of collection, after eight hours, or after 24 hours.
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