Overreliance
on the results of PCR tests (1)
In 2006, the CDC (2)
warned against it regarding false diagnosis of a respiratory illness
but their warning is being ignored
by all for the PCR testing on Covid-19
Disclaimer
Originally
published on July
21st, 2021
A
guest document by Ricardo de Valencia
INTRODUCTION
During the outbreaks of respiratory illness mistakenly attributed to
Pertussis (3)
in 2004-2006 (4)
-- a
respiratory disease
that, like Covid-19, is "complicated
by nonspecific signs and symptoms" -- PCR testing produced near
100% false positives at two hospitals and one community when used on
groups
of symptomatic individuals. (5)
The false positives (cases interpreted as positive for Pertussis when
tested
by
PCR) were confirmed as
false cases of the disease when
the samples were submitted for isolation analysis by culture (6). According
to the CDC, "culture is a reference
standard and 100% specific" (5) in the diagnosis of
Pertussis.
As a result, the CDC concluded that there is an "overreliance on the results of PCR assays",
pointing to "limitations of relying
solely on PCR assays to confirm pertussis". (5)
Their
acknowledgment of the problem, however, was only partial and the
significance of the
events were downplayed,
by merely labeling as "limitations" those results that, taken together
from
the three hospitals involved, were a total predictive failure: 414
false cases out of 415 PCR-positive samples from
symptomatic patients.
What significance or implications does this have for the Covid-19 PCR
tests?
DETAILS
First of all, let us look at the specific figures. The episodes that,
regarding the false Pertussis outbreaks of those years, demonstrated
the
resounding failure of PCR as a tool for predicting and confirming the
disease, took place in the context of three different hospitals:
Hospital
at New Hampshire, 2006.
Positive PCR: 98 cases. Confirmed when
submitted for isolation by culture: 0 cases.
In May, a hospital in New Hampshire
began PCR testing for pertussis on symptomatic health-care
personnel. By
June, of the 98 suspected pertussis cases identified by positive or
equivocal PCR results, none yielded B. pertussis when submitted for
isolation of B. pertussis by culture.
Hospital at Massachusetts, 2006.
Positive PCR: 32 cases. Confirmed when
submitted for isolation by culture: 0 cases.
In October, a hospital initiated enhanced screening (8) of symptomatic
health-care personnel with suspected pertussis. By December, of the 32
specimens which had tested
positive for pertussis by PCR, none
yielded B. pertussis when submitted for isolation of B. pertussis by
culture.
Community around a hospital in
Tennessee, 2004.
Positive PCR: 284 cases. Confirmed when
submitted for isolation by culture: 1 case.
During a 2-month period, many people in the community who visited
health-care providers with
pertussis symptoms were evaluated for
pertussis. Of the 284 symptomatic persons who where positive when
tested by PCR, only the sample of a person (the infant whose case
motivated the screening of the community) yielded B. pertussis when
submitted for isolation of B. pertussis by culture.
The application of PCR tests to clinical diagnosis is something that
the inventor of PCR technology himself had already denounced (7): it is a
technology capable of detecting extremely
small
quantities of genetic material (from viruses, bacteria or other living
organisms) that may not pose a risk to a person (in asymptomatic cases)
or may not be the cause of the disease manifested in a patient (in
symptomatic cases).
PCR tests, by giving YES/NO results for the presence of a molecule but
not a precise and reliable
measure of the amount found, cannot
determine the probability of the risk of disease on a person, even less
can they
confirm the disease. In any case, these tests would serve to exclude one infectious agent among
several possible in a sick person.
The false outbreaks of Pertussis described in the CDC's report (5) illustrate the real
danger of using PCR tests for screening (8) or diagnosing a disease,
a real
danger which is not a mere accident caused by ill-designed tests. It
is a problem inherent to the concept itself of PCR and comes with the
interpretation of the results - as if positive results were a clinical
confirmation of
the disease when they are only a confirmation of the presence of some,
maybe only traces of, genetic material.
Lessons allegedly learned and advice
from the CDC...
The CDC, in their report evaluating those events of suspected
Pertussis, concluded: (5)
The outbreaks described in this
report illustrate the limitations of
relying solely on PCR assays to confirm pertussis.
PCR is an important tool for diagnosing
individual cases of pertussis in persons for whom a high index of
suspicion exists and for whom timely treatment and PEP are essential.
However, the positive predictive value can
be lower if PCR is used as a screening tool without
culture confirmation during a suspected pertussis outbreak.
Overreliance on
the results of PCR assays can lead to
implementation of unnecessary and resource-intensive control measures (e.g., case identification, antimicrobial
treatment, furlough of ill persons, and administration of PEP). In
outbreak
settings, positive PCR results
should be interpreted in conjunction with epidemiologic investigation, evaluation of
clinical symptoms, and confirmation by culture.
CDC recommends timely collection and
testing (early in the course of illness and during the initial stages
of the outbreak) of nasopharyngeal specimens for culture in at least a
subset of persons who are
symptomatic to confirm
pertussis as the etiology of the outbreak. Absent or
inconsistent supporting data
and negative pertussis cultures in appropriately collected specimens should prompt
testing
for alternate pathogens.
... neglected for the Coronavirus
Crisis:
It is very disturbing to see that each of these recommendations or
lessons allegedly learned from the Pertussis pseudo-epidemics in
2004-2006 are being
completely ignored in the massive testing on the population for the
Covid-19 epidemic:
(a) There is an overreliance on the
results of PCR
assays, which leads to implementation of unnecessary and
resource-intensive control measures.
(b) A massive number or PCR
tests are being conducted on
asymptomatic people. Testing for everyone is promoted, whether there
is a "high index of suspicion" or not.
(c) Positive
PCR results are taken as the sole basis for "confirmed cases", without
evaluation of clinical symptoms and confirmation by culture.
Is the CDC a fair judge for PCR
testing?
This particular statement by the CDC is very intriguing:
"PCR
is an important tool for diagnosing individual cases of pertussis in
persons for whom a high
index of suspicion exists and for whom timely treatment and PEP
are essential." (5)
Through the reported events in New Hampshire, Massachusetts and
Tennessee in 2004-2006, it was demonstrated that PCR tests for
Pertussis were not reliable at all for confirming symptomatic cases.
But the CDC want us
to
believe that they still are useful for "some" symptomatic cases, those
in
which there is a "high index of
suspicion".
When we read that, we wonder: If a physician has to determine that a
patient has a "high index of
suspicion" to know (before knowing) whether or not the PCR is
going to be valid as a "diagnostic tool", then, what is the real predictive or diagnostic value of
the PCR? To make a rough simile: this is like being sold a moisture
detector and being told that "It is a great tool for detecting
moisture, but you would better make sure, by other means, that the
sample you
want to test is full of water."
Now, regarding this statement:
"However,
the positive
predictive value can be lower
if PCR is used as a
screening tool
without culture confirmation during a suspected pertussis outbreak."
(5)
We can comment: In New Hampshire, Massachusetts and Tennessee, PCR
tests were used for the systematic examination ("screening") of cases
in symptomatic people.
Out of a total of 415 PCR positives in the three scenarios, only the
case
of one person was
confirmed as valid. This is the situation they describe by saying that
"the predictive value of PCR
positives can be lower".
Only "can
be lower"? Would it not be
fairer to say that the predictive value of PCR tests for Pertussis was
shown to be worthless?
CONCLUSION
If anyone still did not believe that PCR technology is inappropriate
for the screening (8)
and diagnosis of cases of infectious diseases, the
failure in
the false Pertussis crisis should serve as a practical demonstration.
Or, at least, for those reluctant to qualify it as a failure, this
should be taken as
an indication that something is
wrong in the interpretation of PCR tests for diagnosis and screening.
But, then,
where is the concerted and systematic
effort to assess the real clinical value of the Covid-19 PCR tests by
systematically comparing them with the
culture isolation test?
The CDC's attempt to downplay as mere "limitations" the failure of PCR
testing in the 2004-2006 false Pertussis events - even with the numbers
in
the
face of it - illustrates the CDC's lack of will to provide truthful
conclusions regarding the dubious clinical value of PCR tests.
But the audacity is even greater when we see that the
recommendations proposed by the CDC from that events are
being completely neglected for the Covid-19 epidemic.
NOTES
(1) PCR:
(Polymerase Chain Reaction) The technique and tests that is being used
almost
universally worldwide to define "confirmed cases" of Covid-19. For each
disease, one or more specific PCR tests may be developed that are
expected to
detect certain points in the genetic material (RNA or DNA) of the
infectious agent (virus, bacteria, etc.) to which the disease is
attributed.
(2) U.S.
CDC: Centers for Disease Control and Prevention, USA, is the
national public health agency of United States.
(3) Pertussis:
also known as whooping cough, caused by the bacterium Bordetella
Pertussis.
(4) The 2004-2006 events, as
narrated by The New York Times: Faith in
quick test leads to epidemic that wasn't
(5) CDC Report: Outbreaks
of Respiratory Illness Mistakenly Attributed to Pertussis -- New
Hampshire, Massachusetts, and Tennessee, 2004-2006. Quotes
reproduced here are with our highlithing.
(6) Isolation
by culture / In vitro culture: It is a test in which a sample of
material extracted from the patient is placed on a glass plate in the
laboratory (or equivalent substrate) in conditions favoring that, if
the sample contains the expected infectious agent (a particular virus,
bacteria, or living organism), the suspected infectious agent will
reproduce. If, after a specified time, it is observed that a
characteristic chemical effect or signal has been produced in the
culture, it is interpreted that the virus/bacteria/whatever has
reproduced and it is "infectious". If it is a virus, it is said that
the sample contains "active", "viable" or "infectious" virus, which are
synonyms for "capable of reproducing".
(7) The real reason for the misuse of PCR tests
(8) Screening:
(In reference to infectious diseases) The operation of systematically
subjecting all or most members of a population (e.g., hospital health
personnel) to a rapid medical evaluation, typically involving a rapid
clinical test for signs of infection. The people tested may not exhibit
previously any signs or symptoms of the disease, or they might exhibit
only one or two symptoms, which by themselves do not indicate a
definitive diagnosis.
Published on July 21st, 2021
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