A new study led by researchers at the University of St. Andrews in Scotland has revealed that COVID-19 patients are most contagious in the first 5 days after their bodies show the symptoms.
A systematic review and meta-analysis conducted by the team at the University included 98 studies conducted on 7,997 patients who were infected by coronaviruses that cause COVID-19, severe acute respiratory syndrome (SARS-CoV-1), or Middle East respiratory syndrome (MERS-CoV). 81 percent (79) of these studies involved COVID-19 patients.
The results from the study reiterate the importance of early case identification and quarantine.
The studies revealed that infected individuals continued to have the virus (shed the virus) on average, 17 days in the upper respiratory tract, 14.6 days in the lower respiratory tract, 17.2 days in stool, and 16.6 days in serum.
Virus shedding is a phenomenon where the host-virus (the virus which was entered into the person’s body to infect them) replicates inside the body and is released into the environment while the infected person talks, exhales, eats, and performs other normal daily activities.
The longest times of shedding among the studies were 83 days in the upper respiratory tract, 59 in the lower respiratory tract, 35 days in stool, and 60 days in serum.
Presence of Virus
Researchers state that eight studies that used respiratory samples from patients in their first week of illness successfully cultured live virus, but no live virus was found in any sample collected after 9 days after symptom onset, even though the infected individuals continued to have high viral loads.
The study reveals that COVID-19’s viral load peaked in the upper respiratory tract, considered to be the primary source of transmission, in the first 5 days after symptom onset.
The viral load for SARS-CoV-1, which caused SARS peaked at 10 to 14 days while MERS-CoV peaked at 7 to 10 days. Researchers observed that the quicker viral load associated with COVID-19 could be the reason which spreads the pandemic faster in the community while increasing the difficulty to contain.
The study reveals that while there is no difference in viral load peaks in COVID-19 victims with and without symptoms, faster clearance of the virus among asymptomatic patients suggests that they have a smaller window to infect others compared to COVID-19 cases with symptoms.