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What is the limit of detection of the KnowNowᵀᴹ Test?

The Limit of Detection (LoD) is the smallest amount of virus in a sample that a given device can consistently detect.

The Liverpool School of Tropical Medicine carried out an analytical study of the KnowNowᵀᴹ test, which determined that the LoD is 500 plaque-forming units per millilitre (PFU/ml). Based on accepted models of viral load in disease progression, this very low LoD suggests that the KnowNow test can detect infected people as early as day 3 to 4 of infection. This is before they become highly infectious, and a day or two earlier than most tests available.

In the absence of a single study that compares the LoD of KnowNowᵀᴹ to that of other tests, it is not possible to do a like-for-like comparison of the LoDs of different lateral flow tests determined by different studies. This is because there wouldn't be parity across cell cultures and strains of the virus used in the different studies. Additionally, it's important to consider that what the KnowNowᵀᴹ test detects is fundamentally different from other tests. KnowNowᵀᴹ is a true infectivity test which looks exclusively for the spike protein only present on active SARS-CoV-2 viruses. Whereas other lateral flow tests detect the nucleocapsid protein encapsulated in the centre of the virus, which can be present whether the virus is active or not.

The PFU/ml measure, as used in the Liverpool School of Tropical Medicine KnowNowᵀᴹ analytical study, is a measure of only the number of virus particles capable of forming plaques in a given sample - viral particles that are defective or which fail to infect their target cell will not produce a plaque and so are not counted by this measure. No inference can be made about the relationship of PFU to the overall number of viral particles in the sample, since this will differ from sample to sample.

Since the KnowNow test specifically detects infectious viral particles only, an LoD measured in PFU/ml is an informative and appropriate measure. However, for other lateral flow tests which indiscriminately detect active and inactive viral particles, an LoD referencing PFU/ml is not particularly informative or comparable to the KnowNowᵀᴹ LoD. For example, the sample used to determine LoD may have had a very low PFU/ml, but many inactive viral particles which were detected by the test. Ultimately, other lateral flow tests are not true tests for COVID infectivity, they do not detect only infectious virus like the KnowNowᵀᴹ test does.

If you'd like to read more about this subject, we recommend reading this paper. It argues that the "Limit of Detection matters and directly impacts efforts to identify, control, and contain outbreaks during this pandemic" since "higher LoD are likely to miss nonnegligible fractions of infected individuals." It also makes the case that LoD values for tests should be benchmarked against a universal standard and readily available in the public domain to enable like-for-like comparison of SARS-CoV-2 detection methods.

How should KnowNowᵀᴹ tests be stored?

KnowNowᵀᴹ Tests should be stored between 2 and 30 degrees celsius, which means it's fine to store it at room temperature in the UK's mild climate.

There's no need to store it inside a fridge, unless you're expecting extremely hot weather. If you do choose to refrigerate the test though, just make sure it comes to room temperature before using it.

The KnowNowᵀᴹ Test device should also be stored still sealed in its foil pouch. Once removed from the foil pouch, it should be used within one hour.

How does KnowNowᵀᴹ compare to COVID-19 PCR tests?

KnowNowᵀᴹ offers two key benefits over polymerase chain reaction (PCR) tests.

The first benefit is that the KnowNowᵀᴹ test needs only a saliva sample, which can be taken easily and comfortably from the mouth. PCR tests usually need a nasopharyngeal, anterior nasal or tonsil sample, all of which are painful and unpleasant for the individual being tested and more challenging to collect effectively for the clinical professional administering the test. No one wants to be made to cry or gag, or make someone else cry or gag, on a regular basis!

The second benefit is that the KnowNow test uses its unique detection mechanism to determine whether an individual is actually infectious, whereas PCR tests identify whether SARS-CoV-2 viral matter is present in an individual's body, regardless of whether it is already inactive.

Although PCR tests have been seen as the "gold standard" test for the SARS-CoV-2 virus, they do have a number of drawbacks. Laboratory processing is required, meaning that there is a delay before results can be returned, and the associated costs are relatively high. Also the detection mechanism does not specifically identify whether individuals are infectious. In fact, PCR tests detect the virus long after the infectious period, and individuals can continue to test positive for a mean of 17 days after they have stopped being able to infect others (source). This means that people who are not infectious are unnecessarily quarantined as a result of a positive PCR test.

Can anyone order KnowNowᵀᴹ Tests?

At the moment, KnowNowᵀᴹ Tests are for professional use only, meaning that they need to be administered by a trained healthcare professional. This means that we can take orders from organisations that have in-house or outsourced healthcare professionals who can perform the tests, or testing service providers.

However, since the KnowNowᵀᴹ Test needs just a saliva sample, it is much easier to administer effectively than other similar tests, and still return highly sensitive results. So we are investigating whether specially-trained, competent individuals could be approved to administer KnowNow tests as well.

We are also in the process of trialling and seeking approval for a variation of the KnowNow test which could be administered by individuals themselves.

What does a negative test result look like and mean?

Negative KnowNowᵀᴹ Test Result

If there is one red line visible next to the "C" in the KnowNow device test results window, and no line at all next to the "T", then the test result is negative. This indicates that no SARS-CoV-2 antigen has been detected in the sample.

Isn't lateral flow testing less good than PCR testing?

There have been questions raised around the sensitivity of rapid lateral flow antigen testing for SARS-CoV-2 as compared to PCR testing. However, these questions have been strongly challenged by the scientific community.

PCR tests identify the presence of the SARS-CoV-2 virus in the body, regardless of whether the virus is actively infectious. The PCR testing process amplifies the genetic code of the virus so that even minuscule amounts of the virus in the sample can be picked up. This makes for a powerful test, but since viral fragments can linger in the body for weeks even after the infection has cleared, infected individuals being tested using PCR will show as positive for a median period of 22–33 days in total. On the other hand, most people infected with SARS-CoV-2 are contagious only for 4–8 days.

So whilst PCR testing for SARS-CoV-2 may have been considered the "gold standard" test up until now, it will by definition show different results when compared to lateral flow tests which aim to identify individuals based on viral loads which suggest they are within their infectious window. This discrepancy between what each test is actually testing for has caused some issues where PCR testing has been used to evaluate the effectiveness of lateral flow tests, such as in the mass testing rolled out in Liverpool in November 2020.

The KnowNowᵀᴹ Test goes a step beyond other lateral flow tests with its unique, patented detection mechanism which only shows a positive result when live infectious virus is identified in the sample. As a result, PCR tests will similarly show different results to the KnowNowᵀᴹ Test in certain cases, since they will show positive results even for individuals outside of their infectious period.

For a much more comprehensive and referenced answer, you may like to read "Clarifying the evidence on SARS-CoV-2 antigen rapid tests in public health responses to COVID-19" from the Lancet.

How long will it take a qualified clinician to administer each test?

From our own studies with partners, we estimate that a clinical professional can administer one test every 3.5 to 4 minutes. This assumes that they collect saliva samples from individuals, set the KnowNowᵀᴹ Test devices aside to develop for 15 minutes, and collect samples from further individuals before reading the results from earlier tests.

What is a KnowNowᵀᴹ Test?

The KnowNowᵀᴹ Test is the UK's only on-the-spot COVID-19 test that uses just your saliva to tell you if you are currently able to infect someone else with COVID-19.

Unlike other tests, the KnowNowᵀᴹ Test won't give you a positive result if you have been exposed to the SARS-CoV-2 virus in the past, but are no longer able to infect other people.

How specific is the KnowNowᵀᴹ Test?

The KnowNowᵀᴹ Test's specificity is 99.9%. In more than 300 negative patient saliva samples, it hasn’t returned a single false positive result.

This is so important for getting life back to normal. We don't want anyone to be stopped from going to work, heading off on holiday or socialising at events, when actually it would be perfectly safe for them to do these things.

Specificity is particularly important when disease prevalence is low and tests are intended to be used at enormous scale. For example, if a test with just a 3% false positive rate is used on one million people per day, that would result in 30,000 people per day being falsely identified as infectious with COVID-19 and being unnecessarily asked to self-isolate.

Who makes the KnowNow Test?

The KnowNowᵀᴹ Test has been invented, developed and manufactured in the UK by Senseutics Limited, trading as Vatic.

Are you taking shortcuts or risks by developing the KnowNowᵀᴹ Test so quickly?

No, we're not taking any shortcuts or risks. The KnowNowᵀᴹ test has been precisely developed, rigorously tested, and approved by the necessary bodies.

As with COVID vaccine development, the speed at which we’ve been able to move has been accelerated by the enhanced support and focus afforded to the sector by all stakeholders, such as the government, the pharmaceuticals industry, academic institutions and so on.

We have conducted two clinical studies. The first was a UK Government-based study across ten UK hospitals; the second was with Liverpool School of Tropical Medicine. We have also carried out our own analytical assessments, as well as two Public Health England analytical assessments.

The KnowNowᵀᴹ Test has been CE marked for professional use within a healthcare context and is approved by the UK's Medicines and Healthcare products Regulatory Agency (MHRA).

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