The Polymerase Chain Reaction (PCR) test was developed by Dr Kary Mullis for which he was awarded a Nobel Prize. He developed it for use within a clean laboratory environment only to help detect the existence of a known sequence of DNA/RNA present only in the tiniest amount amongst other known sequences that it would be virtually impossible to detect by any other means. I’ve added bold enhancement to this explanation to accentuate a crucially important subtlety that it is essential to grasp in order to understand why PCR is totally inappropriate for disease diagnosis in a field clinical situation.
Consequently, it has been widely used in molecular biology to amplify and detect changes in a DNA/RNA sequence within an already known sequence in order to detect a mutation and thus recognise a different strain of a virus or bacterium, or to confirm that some other intended DNA/RNA manipulation has occurred.
As Dr Kary Mullis explains himself, PCR testing was not developed for and should NOT be used to diagnose disease and infer whether an individual is infective.
In order to understand why he was so adamant about this we need to understand the basics of the PCR process itself.
PCR Test Simplified Overview
- The genetic material (double helix DNA or single strand RNA) to be tested is extracted from the virus/bacterium/cell and filtered to isolate it.
- If the original genetic material is DNA, then it is heated to split it into 2 single strands ready for the PCR amplification process. Single strand RNA as found in some viruses doesn’t need this step.
- “Primers” are added which attach to the specific short sections of the overall single DNA/RNA that are being looked for.
- A polymerase enzyme then builds a complementary nucleotide strand section using the primer as the template. This means that if the looked-for section on the original DNA/RNA isn’t present, the primer will not bind and no new strand will be generated.
- Steps 2-5 are repeated for each cycle before detection.
When the original genetic material includes the looked-for sequence, each cycle of the PCR process doubles the starting amount which means it increases exponentially at each cycle, i.e. 1 becomes 2 becomes 4 becomes 8 becomes 16 etc. There is research that explains that if a positive PCR test result for SARS-CoV2 is only obtained by detecting the looked-for sequence following amplification of the original sample through more than 23 PCR test cycles, then the original sample did not contain sufficient genetic material to be considered infectious, assuming it came from a whole viable organism. For COVID testing, and many of the PCR tests now being inappropriately used to diagnose disease, the PCR test is being cycled more than 40 times. If you are presented with a PCR Test result it is therefore meaningless without knowing this Ct number that denotes how many cycles were performed to obtain the result.
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The amplified DNA/RNA is then detected and analysed using one of several available methods.
There are some fundamental limitations with the PCR Test that Dr Kary Mullis himself recognised and acknowledged which explains why he specifically said that his PCR Test developed to be used in a strictly controlled “clean” laboratory environment should NOT be used to diagnose disease based on processing a dirty, highly contaminated clinical source.
It is crucial to understand that PCR only detects the presence of a selected short sequence of genetic material, not the whole sequence of the whole organism. It will therefore detect this sequence whether the organism it came from was viable at the time of swabbing, or whether it was a residual fragment having already been recently dealt with successfully by the immune system, or had been otherwise broken down and shed by another individual and was an incidental finding on/in the individual being swabbed.
Analogy
An analogous example might help make this clearer as to how dodgy using PCR testing to diagnose disease is. We know that DNA is present in dead skin cells left by a criminal at the scene of a crime. The human genome varies between individuals at certain points called Single Nucleotide Polymorphisms (SNPs) dotted throughout the genome. It takes 35-50 SNP matches to reliably place a criminal at the crime scene, and it can only do so at some unknown time. If there is enough other evidence to suggest the criminal was there at the time the crime took place, then the SNP matches will help in convicting them long after the crime took place and long after they left the scene of the crime. Even with the SNP matches, without other information to suggest the timing is correct, it is not sufficient to confirm who did the crime. The whole SNP matching scenario also has to take into consideration the incidence of each SNP change found in the whole local population, and therefore the likelihood of the combinations of SNP changes found together being significant.
If only a short PCR primer length of DNA sequence including a single SNP location were used in the above scenario it would be insufficient evidence to reliably convict anybody. Some SNP changes will be very common amongst a significant proportion of the population. Some SNP changes will be common only to all close relatives of the criminal. Only by having 35-50 SNP matches is it considered sufficiently identifying within the human species to place a single individual at the crime scene (at some point in time). Some SNP changes may well be common to other species too but given that only the human genome is being considered and compared for a criminal investigation this doesn’t have to be taken into consideration. A criminal wouldn’t get very far if their defence against the SNP matches was based on the same matched sequences being present in another species, such as “The cat did it”, or “The banana pulled the trigger”!!! It’s laughable of course, but using the PCR test as it is currently being done is potentially doing the same thing.
An infectious disease situation can be considered to be almost an exact parallel of the above crime scene scenario, where a pathogen (criminal) causes expression of the symptoms (the crime) in the victim. The crucial difference however is that there are a range of possible pathogens (different species) that are likely present that can cause broadly similar symptoms. Most infections are mixed, even if one predominates.
Microbial soup
People, animals and plants exist in a microbiome soup of bacteria, viruses, protozoa, fungi etc – including not just whole organisms but fragments of them too according to their lifecycle stage, immune interference, and/or influences from other elements of the microbiome that are in competition with each other. All of these pathogens are constantly mutating too, and will exist in different variant forms; some that we know about, and others that we don’t. We certainly don’t have all possible genetic sequences for the whole microbiome within a swabbed area, let alone know which detected sequence belongs to which individual in the microbiome!
With the best swabbing technique and will in the world, any swab taken from a person or animal will inevitably be a sample of the microbiome soup (plus contamination) at that area. It will contain microorganisms of all types of unknown genetic sequences and will contain other cells too – from the individual being swabbed plus whatever other sloughed cells they might have on them, or have breathed in from the environment. I would expect that unless the person doing the swabbing is wearing a Hazmat suit there will also be their cells and contamination from their clothes etc too. Under those circumstances, cycling a PCR test 40+ times has a significant chance of a false positive, by which I mean the result will be clinically insignificant.
Question: Which of the following 8 veterinary viruses is Avian Influenza?
Answer: I don’t know if any of them are, but if any or all happen to contain the looked-for sequence known to be present in the Avian Influenza virus, then positives will all be labelled as such, and the individual (bird/cattle/person) will be diagnosed as having Highly Pathogenic Avian Influenza (HPAI) and will be subject to whatever measures are designated for that species and their in-contacts.
The same principle applies to any other virus or other pathogen potentially being looked for using PCR. If there is a cull policy in place then that individual, and maybe all in-contacts within that cohort, will be euthanised on the basis of the above test result.
Avian Influenza “detection” by PCR is currently happening in the USA on all types of farms with pressure to increase how widespread and how frequently screening will be carried out. This is inevitably leading to a high degree of false positives for the reasons explained above, but even if these factors could be eliminated there is still likely to be a high level of false positives for reasons explained by Prof Norman Fenton in the following video.
Even where Avian Influenza has caused symptoms, they are only minor and transient and only expressed in a small minority (approximately 10%) of potentially infected individuals. The best thing that can happen is for these cattle to be allowed to develop their own immunity that will protect them in future. There is little to no risk of them dying, or any in-contact human farm workers. It is incredibly bad clinical practice to cull unnecessarily, or to consider vaccinating for a disease that has been around for many years with no real risk.
There have been large numbers of deaths in seals and sea-lions, and some other species that have had low numbers of deaths, but given how diagnosis is being carried out, were they “with” or “from” Avian Flu? It’s very difficult to know the true situation. Were they immuno-compromised for some other reason with a concurrent disease?
Were they the victim of a deliberately released and engineered dangerous strain in order to set up the current scenario? In all honesty I wouldn’t put it past people given what we’ve witnessed openly in recent years.
This might sound like a conspiracy theory, but we know such dangerous gain of function research has been carried out on Avian Influenza. We know because the former leader of the CDC in the USA, Robert Redfield, has admitted it!! Avian Influenza has been subject to significant gain of function research, including working out which 5 mutations would be necessary in order to increase human infectivity with presumed resultant high mortality. In order to know this, it means that strain has already been created. Robert Redfield also stated that he considers the greatest risk from it to be from a laboratory leak as happened in Wuhan from COVID than from natural mutation. The reason it’s an unlikely natural mutation is that a virus with a high mortality rate doesn’t survive very long if it significantly debilitates and kills a high proportion of its hosts.
Scaremongering
Even in those rare human cases worldwide over the last 20+ years where there has been a death, it occurred in individuals whose health was significantly compromised. In others, symptoms have cleared up in a few days. No farm workers have died in Texas where cattle have been diagnosed recently either, so the idea that any humans (farm workers or veterinarians) are at “high risk” is equally absurd. Only four human infections have been reported among the hundreds of thousands of people who work at USA poultry and dairy farms. Nevertheless, Finland is now offering a novel mRNA “vaccine” to these people regardless of the fact that the risk of dying from the jab is significantly higher than from the disease. To be clear, nobody is at high risk unless they are immunosuppressed and unhealthy already.
The fact that the WHO jumped at the idea that a Mexican man had died from an H5N2 infection indicates how desperate the WHO and others are to make Avian Influenza into the next pandemic, even though all the preparations have been made in regards to H5N1 - a totally different strain! They’re even planning a “Bird Flu Summit” - the next “Event 201” like they did for a dry run of supposed coronavirus pandemic in September 2019. (Link in resources)
The only farm worker who had symptoms was diagnosed with “pink eye” (conjunctivitis). A swab from his eyeball was “positive” on PCR but not found in the respiratory tract. The pink eye may not even have been from a virus, but could have been from dust, rubbing the face/eye on something or some other cause with an incidental HPAI contaminant. If HPAI was causative of his pink eye, he recovered very quickly with no systemic effects. To cull animals on this basis is veterinary negligence at best, and criminal in my opinion.
Update Dec 2024: There has been a report on the US CDC website that H5N1 Avian Flu antibodies were found in blood samples of horses from Mongolia. Only 9 horses had detectable antibodies on ELISA tests from a total of 997 samples from 24 herds of horses, none of which had any symptoms at the time of testing or had demonstrated any respiratory symptoms in the past. To conclude that because horses can get Equine Flu that therefore horses could potentially become a vector for Avian Flu is pushing the boundaries of desperation IMO. Is this laying the groundwork to justify PCR testing horses in private ownership at some point in the future? All the more reason to understand PCR testing methinks.
Advice for farmers
If a veterinarian turns up on your farm wanting to take swabs for PCR testing from asymptomatic individuals with the risk of culling positive individuals and in-contact birds/animals hanging over them, my advice would be to refuse access on the basis that you are obliged not to expose your herd/flock to poor clinical practice and abuse. There would be a high risk of false positives in this situation. If your flock/herd is showing symptoms of disease consistent with the pathogen that would be tested for then this is a different scenario and PCR testing might be justified provided it is being run in parallel with other culture and isolation tests to ensure there is minimal risk of a false positive.
Similarly, as we know from use of the mRNA jabs for COVID in people, widespread use for a virus that readily mutates is only ever likely to increase pressure to mutate in ways that increases infectivity and pathogenicity over time. As explained in the Open Letter of Concern sent to the UK Veterinary Medicines Directorate (VMD) regarding use of the mRNA platform in animals, the injections themselves come with considerable risks to the individuals they are used on and potentially to our food chain.
We know that the UK Government signed a huge contract with Moderna committing to purchasing £250m worth of mRNA jabs. My concern when human uptake is low, as it will be now that peoples’ suspicions have been raised by the COVID jabs, is that the veterinary market will be seen as the contractual safety net.
Farmers and everybody need to be aware of the dangers of using the mRNA platform within our food chain, not just because of their effects on the animals, but how they can potentially spread prions to the meat, environment, plant crops and us. See my blog on prions for details. They present a similar risk to our pets too.
Summary
If clinicians truly understand the PCR Test (they should know what they’re doing if they’re going to use it) then they shouldn’t be prepared to use it for field disease diagnosis in isolation, and only in conjunction with microbiological isolation and identification which takes longer to get results. Limitations other than a temporary movement restriction shouldn't be made based on PCR alone, although even this can have significant financial implications for farmers who are unable to meet their contractual obligations to supply birds/pigs/beef/lamb of a certain age and body composition etc.
If a clinician doesn't fully understand a medical instrument such as a PCR including its limitations as well as its uses, it shouldn’t be used. If they truly understand the PCR but are still prepared to use it for field diagnosis in an inappropriate way, then I consider that (s)he is negligent at best. Blindly trusting the PCR test manufacturer is no excuse.
Resources
Avian Influenza “201” event dry run: Bird Flu Summit
A slightly different version (because I had a word limit) of the above explanation has been published by the Journal of Independent Medicine as below, although they put the picture of the 8 different viruses in a supplement instead of within the relevant place within the text.
https://journalofindependentmedicine.org/articles/v01n03a05/
The pdf is an earlier proof version sent when they were originally going to include the Figure 1 at the end of the paper rather than in the supplement, but is otherwise exactly the same. Open it by clicking on the pdf image and then download it for reference and to show others.
Email to the VMD
On the basis of the above understanding, I sent the following FOI to the UK Veterinary Medicines Directorate (VMD)...
Dear VMD
It has come to my notice that PCR testing is being inappropriately used within general veterinary practice in a manner that Nobel Prize winner Kary Mullis PhD who invented the PCR test stated it should not be.
My full understanding of PCR has only evolved in recent years since the PCR test hit the news because of COVID. Kary Mullis PhD developed PCR in order to identify the occurrence of known mutations during genetic experimentation in a laboratory situation, and as such was in effect detecting the qualitative and quantitative presence and ratios of 2 known sequences only. This is a very different proposition than looking for 1-3 short nucleic acid sequences amongst a myriad of microorganisms as occurs naturally in the microbiome that would be picked up on a swab during a clinical examination. Any number and variety of unsequenced microorganisms may include one or more of these looked for sequences which would in effect identify them as something they are not and would therefore amount to a false positive that there is no way of identifying. Animals, including negative tested in-contacts, may well be unnecessarily slaughtered on the basis of such a false positive result which would also skew DEFRA's perception of the extent of an "outbreak".
The following esteemed academics Prof. (Emeritus) Norman Fenton, PhD, Prof. Martin Neil, PhD, Dr Jonathan Engler, MB ChB DipPharmMed LLB published the following regarding false positives in PCR testing from cross-reactivity. Whilst the article was written with COVID testing in mind, the principles are relevant across the PCR test board regardless of what is being tested for. https://wherearethenumbers.substack.com/p/does-unacceptably-high-cross-reactivity
There are a number of other ways in which false positives might result, and unless the PCR test has been properly assessed to determine the extent to which each of the following false positive situations can occur, the PCR test has no valid scientific basis for being used in a clinical situation whatsoever, let alone as the basis for justifying a cull.
The following things should be elucidated and defined IMHO for any PCR test before it's authorisation/use, and only then in conjunction with pathogen isolation before declaring a true positive.
Taking the sample
Only birds/animals that are showing relevant symptoms of the disease being looked for should be tested (because when the intrinsic false positive rate of the test is higher than the viral prevalence in the population tested the majority of positives will be false positives. For example, if intrinsic false positive rate of the test is 5% and viral prevalence only 1%, if you test 100 birds you'll likely have 6 positives, 5 of which are false positives. This is why asymptomatic populations should not be tested (as the prevalence of any disease in populations without symptoms is likely zero, so all positives will be false positives).
Likewise, testing should not be done out-of-season for diseases that vary seasonally, as this will yield large numbers of false positives. The true prevalence of disease in periods of seasonal lows is obviously low and more likely to be lower than the false positive rate of the test.
Defining the PCR test primers and what constitutes a positive?
How many and which gene sequences are sought by the PCR test? Normally at least 3 primers should be used, from regions across the genome. They should also define where these sequences have been identified from (in SARS-CoV-2 testing 2 of the 3 sequences that the PCR test contained were from Charité in Berlin (E gene) and from US CDC (N2 gene) but these tested positive for all samples tested, even for control samples (e.g. water) which clearly sets the scene for many false positives. It is therefore important to know which gene sequences any PCR test is looking for and who had defined that sequence, and has it been verified elsewhere, including studies to evaluate the test for each gene sequence across different samples including controls/blanks.
Having verified the different sequences and ascertained their specificity it is then important to know how many target genes must be present in order to declare a positive? As the following letter to the Editor of the BMJ points out, single gene identification testing increases the likelihood of false positives from cross-reactivity. https://www.bmj.com/content/372/bmj.n208/rr-3).
For all PCR results the cycle thresholds should be defined and reported both for the test disease pathogen and for detection of competing pathogens. As Kary Mullis PhD said himself, if you keep cycling the PCR you’ll find whatever you want. That isn’t the objective unless there’s a political agenda. For COVID, Ct > 24 means there is insufficient pathogen present in the original sample to cause a clinical infection and yet Ct > 40 was the standard Ct used with results declared “positive” despite being clinically insignificant. The Ct cut-off for detecting a clinically significant level of pathogen MUST be determined for each pathogen and each PCR test.
Operational false positives
For each PCR test it is important that studies have been done to assess the false positive rate of the test in the field operation situation. This addresses the risk of cross-contamination (as opposed to cross-reactivity) in practice when collecting the samples and in laboratories when processing samples, and whether standardised testing protocols are functioning adequately.
In order to assess these tests themselves the sample sizes of the studies used to evaluate tests should be known so as to be able to evaluate the intrinsic and extrinsic false positive rates of each test. What are the confidence intervals? The less precise the estimates, the weaker the argument for taking any measures in herds/flocks where “positives” occur.
When it comes to respiratory diseases, unless an individual is sacrificed in order to swab the lungs directly it should be established what the likelihood is that a causative pathogen will be able to be collected and reliably identified from a swab of an upper respiratory tract area.
Please provide a list of which veterinary PCR tests are currently in use or are intended to be used, and how they are intended to be used whether alongside pathogen isolation or as a stand-alone test.
Can the VMD confirm that for every PCR test currently or intended for use in veterinary practice that all the above evaluations have been properly carried out, and if they have, please provide copies of the relevant documentation?
Please provide copies of the documentation that stipulates the process for carrying out each PCR test currently in operation, detailing sample collection and laboratory processing procedures including the Ct directions.
Many thanks in advance.
Best regards
Roger
Imagine my surprise and shock when I received the following reply...
Dear Roger,
Thank you for your email.
The VMD understood that PCR tests, you described in your email, are conducted as clinical diagnostic tests in veterinary practices or in the field. VMD does not regulate such in vitro tests and therefore, would not be able to comment. We assume that you would need to contact the manufacturers of the diagnostic kits or agencies such as the APHA or Pirbright Institute who conduct diagnostic testing and surveillances for certain diseases.
Kind regards,
VMD Postmaster
What the VMD have said in their reply is that they do not regulate, authorise or otherwise ensure that the PCR tests in use in clinical veterinary practice have undergone any rigorous scrutiny to ensure that they are as described and fit for purpose.
I replied as follows...
Dear VMD Postmaster (name?!)
Thank you for your email reply to my enquiry.
Your answer begs the question as to who regulates PCR tests (or any other test) authorisation for veterinary use in the UK to ensure that the accuracy and efficacy of any test is as claimed by the manufacturer and fit for purpose?
I would imagine that the vast majority of vets in the UK would automatically assume as I did, that all reagents used within the veterinary arena, whether for testing or treating must be authorised and proven/checked to be as described and fit for purpose. Testing will result in the use of treatment products which are controlled by the VMD. An inappropriate test will inevitably lead to an inappropriate use of one or more treatment products at best, potentially including antibiotics that are supposed to be only used where absolutely necessary due to concerns over AMR.
However, given that DEFRA are basing restriction of movement and cull policies potentially on such PCR results alone, which have enormous implications for individual farms and UK agriculture as a whole, it all seems rather flimsy and open to the current abuse that my original query has highlighted. Where is the hard science to back up such critical actions?
Given that the CVO is head of both DEFRA and VMD, maybe you can forward this sequence of emails to her for comment on this situation.
Best regards
Roger
The VMD replied as follows, along with APHA's contact details...
Dear Roger,
Thank you for your email.
I have contacted APHA (Animal and Plant Health Agency) (Defra) on your behalf to request their advice on this as they carry out diagnostic tests.
More information can be found on their website - APHA laboratory test submissions and price lists - GOV.UK
Kind regards,
VMD Postmaster
Having had no response after a couple of weeks I followed up to the VMD to see if they had received a response. As they hadn't, I resubmitted the above email thread to APHA directly on 08.11.2024.
For some reason it needed clarification although I think it is very clear what I'm saying and asking and the VMD seemed to understand it very well even if they couldn't provide what I was looking for! As yet, I have not received a response from either APHA/DEFRA or the Chief Veterinary Officer.
13.12.2024
I had a response from APHA on 10.12.2024 as follows.
I was not particularly impressed and sent the following ...
Dear APHA
Thank you for your response re the PCR test.
I don't share your opinion that PCR has moved on from when Dr Kary Mullis made his comment on it's inappropriate use in a clinical situation. I'm certainly not aware that he voiced his change of mind before his untimely death in 2019. The fact that you say you only use PCR in tandem with other tests would tend to suggest you don't really believe what you've said either, or you'd be relying on PCR on its own. I really hope you aren't.
Giving the COVID PCR test as your example of how it has moved on and is good practice leaves me in no doubt that you don't understand PCR testing properly at all, as the COVID PCR test demonstrated an extremely high level of false positive results as was explained in my initial request, and was cycled at far too high a rate by the NHS.
Although I asked for the protocols being used in how the PCR tests are being executed your response overlooked this aspect. To perhaps ask more precisely, please inform me as to what Ct cycle rates you are using for Avian Influenza, TB and Bluetongue as these are currently the most pressing PCR tests being used for notifiable diseases that are active at this time to my knowledge. Do you generally use the same Ct rate for all tests or different Ct rates for different pathogen tests?
Best regards
Roger
I expected to receive and acknowledgement with a time frame for their reply, but instead received the following reply with pdf attachment shortly afterwards. I think I hit a nerve!
Dear Mr Meacock,
Thank you for your email correspondence. This was forwarded to APHA Executive Office to respond. Please find APHA’s reply attached.
APHA now consider your correspondence on this topic closed.
Regards
Executive Office
Animal & Plant Health Agency
APHA.CorporateCorrespondence@apha.gov.uk
Observations on the responses by APHA
APHA says "Tests for APHA use (including PCR) are validated according to WOAH (World Organisation for Animal Health) standards and guidelines and then performed under the requirements of ISO17025 standards."
It begs the questions as to who sets the standards and guidelines within WOAH and who ensures that the tests actually meet those standards? It doesn't matter what standards are set if nobody is checking every batch in terms of manufacturing, and given that there will be huge variation in the locations within which field samples will be taken in terms of cleanliness, humidity, and temperature etc it is impossible to standardise those parameters which will have significant implications for the test results. It would be difficult enough to standardise these within a single country, let alone worldwide, or are standards chosen according to the lowest common denominator?!
Who decided that PCR tests are appropriate for use in a clinical situation when Dr Kary Mullis is on video record saying they aren't? A condescending reply that PCR testing has moved on without explaining how it can now be used for dirty sample testing as happens in the clinical field just doesn't cut the mustard with me.
Why is the UK all of a sudden accepting standards and guidelines that aren't enshrined in UK law to my knowledge and that have been set by a globalist body outside the UK jurisdiction?
The ISO standards and AKAS scrutiny is all very well but it misses the point. As an analogy let's consider a commercial kitchen. It can have standardised, recognised equipment inspected at regular intervals for cleanliness and hygiene. There can be chefs who are highly qualified too. But if the produce they buy in to cook with is the lowest grade possible, hasn't been picked at the right time, harvested/slaughtered in the right way, and hasn't been stored properly before it gets to the kitchen, you aren't going to be served with a Michelin starred meal.
To be clear, I'm not criticising the laboratory technicians and staff at APHA who I'm sure do what is asked of them. What I'm questionning is whether what they're being asked to do is appropriate, and is it possble to produce an efficacious and meaningful result that is reliable? This comes down to the circumstances under which the sampling and testing is being carried out.
For example, a test might officially have what sounds like a very low false positive rate (eg <1%), but if it's used to detect a specific pathogen with a very low prevalence, the true false positive rate can be very high and near 100%. This is the essence of Prof Norman Fenton's video on statistics above, yet APHA don't seem to have grasped that significance. This false positive rate will be even higher if an inappropriately high Ct figure is regarded as a positive result, so that even if the identification of the pathogen is correct, it may still not be present in a viable state or sufficient numbers to be clinically relevant to the sampled individual or to be infectious for others.
If you've made it this far I expect you will have realised that the essence of what I'm concerned about is the false positive test rate, yet at no point has APHA tried to address what the established false positive rates are for any of the PCR tests that I queried.
I am left at the same point - that I'm highly concerned that inappropriate use of PCR tests may lead to wrong decisions being made with regards to movement restrictions and/or cull orders. How much faster a PCR might give a result is meaningless if nearly 100% of positive test results are false positives. We have heard far too often of "asymptommatic" carriers being tested which are greatest source of false positives. It doesn't bode well if farms/individuals are going to be tested within exlusion zones around previously identified centres of infection.
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