Infectiousness of covid-19 patients peaks in the first week after onset of symptoms, according to a new study. This study highlights the need for rapidly identifying and isolating cases to control the spread of the virus. The findings of the study are published in the journal The Lancet Microbe
Meta-analysis was used to assess 98 studies on Covid-19, SARS, and MERS. The study was conducted to determine the reason why covid-19 spread rapidly in comparison to the earlier diseases
Study lead author Muge Cevik from the University of St. Andrews in the UK stated, "This is the first methodical review and meta-analysis that has comprehensively studied and compared viral load and shedding for these 3 human coronaviruses."
The researchers covered 98 studies that had 5 or more participants, cohort studies, and randomized controlled trials, 79 focussed on SARS-CoV-2, 73 of which included hospitalized patients only, 8 on SARS-CoV, and 11 on MERS-CoV infection.
From these studies, the authors calculated the average length of viral RNA shedding. They examined the changes in viral load and the success of isolating the live virus from numerous samples collected throughout an infection.
Analyzing the SARS-CoV-2 studies results showed that the average length of time of viral RNA shedding into the upper respiratory tract, lower respiratory tract, stool, and serum were 17 days, 14.6 days, 17.2 days, and 16.6 days, respectively.
The longest period that RNA shedding continued was 83, 59, 35, and 60 days, respectively.
Of the 11 studies that attempted to isolate the live virus, all 8 studies included that used respiratory samples succeeded to culture viable virus within 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 involved in this systematic review managed to successfully isolate live virus past-day nine symptoms in any type of sample, despite persistently high viral RNA loads.
These findings suggest that repeat PCR testing may not be needed in clinical practice to deem that a patient is no longer infectious, as this could remain positive for much longer and does not necessarily indicate they could pass on the virus to others.
Cevik added, "In patients with non-severe symptoms, their period of infectiousness could instead be counted as 10 days from symptom onset."