On April 19, a 48-year-old man from Thekkil in Kasaragod tested positive for COVID-19. What made his case unique was that he had arrived in Kerala from a Gulf country on March 16. The infection was detected a good 34 days after he returned from an area considered to be at high risk for COVID-19 transmission.
Does it mean that the infection in a patient can manifest even after the 14-day incubation period and the 28-day quarantine period? Not necessarily.
Ignored
An epidemiologist in the Health Department, who requested anonymity, told The Hindu on Monday that current evidence on COVID-19 did not support the demand for extension of the quarantine period.
“A few cases have now come to light where reverse transcription-polymerase chain reaction (RT-PCR) tests are turning positive three or four weeks after the patient’s presumed initial contact with another infected person.
In such cases, the presumed time of contact may not have been correct or the infection could have been acquired later,” he pointed out. Otherwise, the patient might have ignored early symptoms or passed them over so that the real incubation must have been shorter. The patient might be asymptomatic or some symptoms might have been because of other causes.
RT-PCR tests detect the presence of viral RNA in human samples. PCR is a process where a few copies of DNA are amplified to produce millions of copies. “RT-PCR tests turning positive are not synonymous with infectivity, the ability of a microorganism to cause infection.
Viral RNA
The test turns positive when viral RNA sequences are present in the sample and can be amplified and detected.
This can happen three days after the infection and can persist several days after the onset of the disease or even days after the patient becomes asymptomatic,” the epidemiologist pointed out.
Usually in cases where the sample tests positive after 28 days, the viral RNA copy numbers are low, less than a lakh. Such cases do not represent the infective stage.
“Infectivity of a sample is indicated by the ability to culture the virus from it. RT-PCR tests to identify subgenomic mRNA, smaller sections of RNA strand, can detect cells in the active replicating phase and presume that they are infective. Studies indicate that infectivity does not extend to more than eight days after the onset of symptoms,” he said.
Two weeks
In such circumstances, extending the mandatory quarantine beyond 14 days or continued isolation of a patient beyond two weeks after recovery does not seem to be necessary.
Extending quarantine to 28 days despite lack of evidence may prove counterproductive because of non-compliance, he added.
