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2020 MEDICAL YEAR
IN REVIEW

Testing for Evidence of the

COVID-19 Virus

By Alan Preston, MHA, Sc.D.

Ever since COVID-19 was present in the USA, the challenge was to determine how fast would
it spread and what harm could it cause, and to whom? In the world of epidemiology, we look at
the incidence rate of a disease as the first onset of the disease. The prevalence of a disease is the
number of people who have already acquired the disease. Capturing the rate of transmission of
any given communicable disease requires an understanding of both.

Early this year (i.e., February 2020), the (CLI) should be tested to rule in/out to 40 to indicate a positive COVID-19?
news agencies reported the number of cases COVID-19. When over 90% of the tests are The implication is many people are labeled
every day based on those tested. The prob- negative, that suggests the public has a high positive for COVID-19 when they should be
lem, in the beginning, was that the correct degree of fear and desire to understand labeled negative. They should be labeled neg-
number of cases in the general population whether they are infected. Their ILI symp- ative because of the viral load. The PCR test
was at least ten times more than the number toms may be related to allergies, a superficial amplifies genetic matter from the virus in cy-
of cases being reported. This created two sig- sinus infection or a postnasal drip that causes cles. If you find a high amount of viral load
nificant problems; one underestimated the a cough or sneezing unrelated to COVID- in a person, fewer cycles are required. The
number of infected individuals and overesti- 19. The challenge for many healthcare pro- greater the viral load, the more likely the pa-
mated the death rate (i.e., case fatality rate fessionals is when to perform a test and what tient is to be contagious. And if it takes 40
CFR) since the death rate is based on the kind of test should they perform? cycles to detect a small amount of viral load,
number of infected cases. And not until mid- There are primarily two categories of then the likelihood that the "infected" person
March did the testing begin in earnest to COVID-19 tests; the PCR test and the An- can pass the virus is significantly negligible.
more accurately determine how many people tibody test. The PCR test is appropriate for Unfortunately, the number of amplifica-
may be infected. The number of tests before current diagnosis for the most part, which I tion cycles needed to find the virus is never
mid-March was less than 60 per day, which will explain in a bit, and the Antibody test is included in the results sent to doctors. If it
increased to 127,000 per day on March 18, used to determine if someone had COVID- were, doctors could tell how infectious the
2020. As of November 2020, there have been 19 in the past. patients are. It is difficult to estimate the
over 1,327,000 per day in the U.S., or The challenge with the PCR test is that the number of tests suggesting a patient is posi-
156,318,000 COVID-19 cumulative tests results are binary; positive or negative. As tive when, in fact, they are, for all practical
performed. The more people tested, the more most physicians understand, a laboratory test purposes, negative. A September 2020 NY
people will test positive; however, as a per- often has ranges. The ranges help physicians Times article looked at three sets of testing
centage of tested individuals, it will hold understand the acuity of the patient based on data that include cycle thresholds. What they
steady and predictable, as it has for a while at a lab value range. The PCR test also has a found was astonishing; in Massachusetts,
6 to 10% tested positive. That suggests that range. The range is based on a cycle threshold New York and Nevada, up to 90 percent of
those who think they are infected with (CT). The current cutoff on most PCR tests people testing positive barely carried any
COVID-19 find out that 90 to 94% of that is close to 40 CT. Suppose the CT is over 40, virus. Tests with cycle thresholds so high de-
population are COVID-19 negative. which suggests a negative test. If the CT is tect genetic fragments that pose no particular
Why would someone get tested, and under 40, that means positive. However, risk to the public. Yet the public policy man-
what kind of test are they receiving? The most PCR tests for other types of viruses are dates have enormous economic consequences
CDC suggests that anyone with influenza- closer to 30 to 35 on the high end. What are when data is overstated, and politicians rely
like illness (ILI) or COVID-like illness the implications of allowing a PCR CT of 30 on data (overstated or otherwise) for man-

22 SAN ANTONIO MEDICINE • December 2020