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People with coronavirus are most likely to be highly infectious in the first week after symptoms appear, new research suggests.
The study, conducted at the University of St Andrews, showed that typically within five days of the first symptoms onset, people were at higher risk of transmitting the virus, highlighting the importance of identifying and isolate cases early.
Genetic material of Sars-CoV-2, the virus that causes COVID-19, can still be detected in patients’ respiratory or stool samples for several weeks, but not alive The virus was found in any type of sample collected more than nine days after symptoms began, the research found.
Lead author Dr Muge Cevik from St Andrews said: “This is the first systematic review and meta-analysis that has comprehensively examined and compared the viral load and clearance of … three human coronaviruses.”
The highest COVID-19 viral load was detected early in the course of the disease.
“It provides a clear explanation of why Sars-CoV-2 spreads more efficiently than Sars-CoV (SARS) and Mers-CoV (MERS) and is much more difficult to contain.
“Our findings are in line with contact tracing studies that suggest that most viral transmission events occur very early, and especially within the first five days after symptom onset, indicating the importance of self-isolation. immediately after symptoms begin.
“We must also educate the public about the range of symptoms related to the disease, including mild symptoms that may occur earlier in the course of infection than those that are more prominent such as cough or fever.
The study, published in The Lancet Microbe, specifically looked at people infected with COVID-19 and mainly those who were admitted to the hospital.
The researchers said the results are only relevant to the self-isolation period of people with confirmed COVID-19, and do not apply to people who simply self-quarantine after contact with someone infected.
Many countries recommend that people with the virus self-isolate for 10 days, which the authors say is in line with their findings, cautiously covering the period of contagion.
Understanding when patients are most likely to be infectious is important to inform effective public health measures to control the spread of the virus.
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The study looked at key factors, including viral load, how the amount of virus in the body changes throughout infection, and viral RNA shedding, the amount of time someone sheds viral genetic material.
He also looked at isolation of live virus, a stronger indicator of a person’s infectivity.
The researchers included 98 studies that had five or more participants, cohort studies, and randomized controlled trials.
Seventy-nine focused on Sars-CoV-2 (COVID-19), 73 of which only included hospitalized patients, eight with SARS, and 11 with MERS.
The highest COVID-19 viral load was detected early in the course of the disease, at the time symptoms begin or before day five of symptoms.
In contrast, SARS and MERS viral loads peaked 10-14 days and 7-10 days after the onset of symptoms, respectively, which explains why transmission of these viruses can be reduced from effectively by immediately identifying, isolating and quarantining people who show symptoms.
