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In a major study, researchers have claimed that infectivity peaks early in Covid-19 patients, highlighting the need to quickly identify and isolate cases before the virus spreads.
The systematic review and meta-analysis of three human coronaviruses, published in The Lancet Microbe, suggests that people infected with coronavirus are most likely to be highly infectious in the first week after symptoms appear.
The report used a meta-analysis to evaluate 98 studies on Covid-19, SARS, and MERS.
The researchers studied all three diseases to determine why Covid-19 has spread faster than previous diseases.
“This is the first systematic review and meta-analysis that has comprehensively examined and compared the viral load and clearance of these three human coronaviruses,” said study lead author Muge Cevik of the University of St. Andrews in the UK.
“It provides a clear explanation why SARS-CoV-2 spreads more efficiently than SARS-CoV and MERS-CoV and is much more difficult to contain,” added Cevik.
The researchers included 98 studies that had five or more participants, cohort studies and randomized controlled trials, 79 focused on SARS-CoV-2, 73 of which included only hospitalized patients, eight on SARS-CoV and 11 on the MERS-CoV infection. .
From these studies, the authors calculated the average length of viral RNA shedding and examined changes in viral load and the success of isolating live virus from different samples collected during an infection.
Analysis of the results of the SARS-CoV-2 studies showed that the mean time of elimination of viral RNA in the upper respiratory tract, lower respiratory tract, feces and serum was 17 days, 14.6 days, 17.2 days and 16.6 days, respectively. .
The longest time for RNA clearance was 83, 59, 35, and 60 days, respectively.
Of the eleven studies that attempted to isolate the live virus, the eight included studies that used respiratory specimens succeeded in cultivating viable viruses during the first week of illness.
Of the studies that also measured RNA viral load, these demonstrated a link between the success of isolating the live virus with viral load levels.
No study included in this systematic review was successful in isolating live virus beyond day 9 of symptoms in any sample type, despite persistently high viral RNA loads.
These findings suggest that, in clinical practice, it may not be necessary to repeat the PCR test to consider that a patient is no longer infectious, as this could remain positive for much longer and does not necessarily indicate that they could transmit the virus. to other people.
“In patients with non-severe symptoms, their contagion period could be counted as 10 days from the onset of symptoms,” Cevik noted.
