Scientists can determine how infectious a Covid-19 patient is

CAPE TOWN- Epidemiologists and public health experts are exploring new research which could help doctors flag patients at high risk for serious infection. Scientists can narrow down a number known as the cycle threshold (CT) value, which indicates how much virus an infected person harbors.

While there are limited studies exploring the correlation between threshold cycle value and the severity of the infection, scientists say the CT value is important as it could help to identify and isolate infectious people. Those with a high viral load are quarantined, while those with insignificant viral load could be asked to quarantine at home.

According to an article in ScienceMag, standard Covid-19 tests identify infections by isolating and amplifying viral Ribonucleic acid (RNA) using a procedure known as the polymerase chain reaction (PCR). This process relies on multiple cycles of amplification to produce a detectable amount of RNA.

The CT value is the number of cycles necessary to spot the virus. If a positive signal isn’t seen after 37 to 40 cycles, the test is negative. However, samples that are positive can start out with vastly different amounts of virus, for which the CT value provides an inverse measure.

Early studies show that patients in the first days of infection have CT values below 30, and often below 20, indicating a high level of virus. As the body clears the coronavirus, the CT values rise gradually.

More recent studies have shown that a higher viral load can profoundly impact a person’s contagiousness and reflect the severity of the disease.

A report in June from researchers at Weill Cornell Medicine found that among 678 hospitalized patients, 35 percent of those with a CT value of 25 or less died. Higher viral load was associated with increased age, comorbidities, smoking status, and recent chemotherapy.

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