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How it plays a role in Covid-19 operator’s high risk, transmissibility, isolation, and contact tracking
As in most of the world coronavirus “Again” and countries are increasing the number of tests they carry out, an issue that is under discussion in the scientific community is whether the molecular diagnostic tests now must give in addition –beyond whether one is positive for the virus or notAnother vital fact: the viral load.
Enough epidemiologists Y other scientists argue that to get a better idea of the extent to which a person can transmit it SARS-CoV-2 coronavirus and thus spread the disease COVID-19, The results of molecular PCR testing It will be very helpful to include an indication of the amount of virus in a person’s body. And this indication is the CT index (Cycle threshold), which is the number of cycles of amplification of the sample by a human being, which must be carried out to exceed the detection limit of coronavirus. The lower the Connecticut, the higher the estimate viral load.
Proponents of the CT index, according to Science, are based on new research showing that This additional information will really help clinicians distinguish between patients at high risk of developing Covid-19 seriously and those who are more contagious, so their contacts should be isolated and traced as a matter of priority..
Although CT is an incomplete indicator, says epidemiologist Michael Mina of the Harvard University School of Public Health, whether it should be added to molecular test results is “one of the most pressing questions today.” However, despite its shortcomings, the knowledge of viral load can be extremely robust. “
Molecular tests, to detect the genetic material of the virus, amplify it Viral RNA through a process called the polymerase chain reaction (PCR), which consists of multiple cycles of sample amplification until there is a detectable amount of RNA. CT shows how many cycles it took to find the virus in the sample, so the PCR machines stop the amplification. If a positive trace of your RNA coronavirus If it is not found after 37 to 40 cycles, then the test is negative, meaning that the virus is undetectable.
The problem is that the tests that come back positive can be very different in terms of CT.. A CT 12 test (that is, it took only 12 cycles of amplification to detect coronavirus) shows that there is at least ten million times more genetic material in the virus than in a sample with a CT index of 35.
An additional difficulty is that not only can the same sample from one person give different CT values on different PCR machines, but also that different samples from the same person can give different CT numbers. (in other words, the presence of the virus in the body varies). This uncertainty has so far slowed down the use of CT, as many clinicians consider it an unreliable indicator, an opinion that others do not share, which is why the issue is being discussed in the scientific community.
Initial studies had shown that patients in the early days of Covid-19 infection had CT values below 30, often below 20, indicating a strong presence of the virus. As time passes and the virus is in a remission phase, the CT value in the tests gradually increases. Recent research has shown that a high viral load can significantly affect a patient’s contagion, but also the severity of symptoms.
A study by scientists at Cornell University School of Medicine and New York University Medical Center on 678 Covid-19 patients found that of those with TC under 25 in their tests, 35% died, compared to 18 deaths. % for those who had a TC of 25 to 30 and only 6% for those who had a TC greater than 30.
“It’s fair to say that a higher viral load is associated with higher transmissibility,” said Dr. Monica Gandhi, an infectious disease specialist at the University of California, San Francisco. “If there are 100 patient files on my desk to keep track of, I will prioritize the people with the highest viral load because they are more contagious,” Dr. Mina said. “We have to stop thinking of people as positive or negative (coronavirus) and start wondering how positive they are,” he added.
Too, Epidemiologists can use the CT index of the tests to draw conclusions about the course not of individuals, but more generally of the epidemic in a population.. If they see a lot of low CT values in the tests, it means that the epidemic is spreading, whereas the opposite occurs when the CT values in the molecular tests increase over time.
But viral load (hence CT) is not a completely reliable indicator, as Gaddy admits. About 40% of SARS-CoV-2 coronavirus carriers remain healthy and asymptomatic, although they may have as high a viral load as those who are sick.
“As a physician, the price of a CT scan is not the only thing I look at. But I find it useful,” said Chanu Ri, assistant professor of epidemiology at Harvard Medical School and Brigham and Women’s Hospital in Boston.
