Coronavirus MOST infectious within five days of onset of first symptoms

The five days after an individual infected with a coronavirus develops symptoms are when they are most contagious, a study has found.

Research by Dr Muge Cevik of the University of St Andrews also found no live viruses in samples taken more than nine days after symptoms appeared.

However, the genetic material of the coronavirus can be detected for several weeks in respiratory and stool samples, but it is not believed to be infectious.

The study, published in the journal Lancet Microbe, looked at the viral load, the amount of virus, detected in the upper respiratory tract soon after infection.

The experts gathered and reviewed 98 articles to inform their conclusions.

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The researchers evaluated the amount of SARS-CoV-2 detected between the mouth and the lungs at different time intervals.

In addition to examining the behavior of SARS-CoV-2, the researchers also evaluated two related coronaviruses, MERS and SARS.

Lead author Dr Muge Cevik, University of St Andrews, said: “This is the first systematic review and meta-analysis that has comprehensively examined and compared viral load and shedding of… three human coronaviruses. “

He found that the level of the virus causing the current pandemic is highest when symptoms start, or before the fifth day of symptoms.

In contrast, viral loads for SARS and MERS-CoV peaked 10 to 14 days and 7 to 10 days, respectively, after symptom onset.

The relatively rapid increase in the amount of the SARS-CoV-2 virus found in the upper respiratory tract is part of the reason it is so contagious, researchers believe.

“This clearly explains why Sars-CoV-2 spreads more efficiently than Sars-CoV and Mers-CoV and is so much harder to contain.

“ Our results are consistent with contact tracing studies which suggest that the majority of viral transmission events occur very early, and particularly in the first five days after onset of symptoms, indicating the importance of self-transmission. isolation immediately after onset of symptoms.

“We also need to educate the public about the range of symptoms related to the disease, including mild symptoms that may occur earlier in the infection than larger ones like cough or fever.

The study specifically looked at people infected with Covid-19 and primarily those who were admitted to hospital.

The researchers said the results are only relevant for the period of self-isolation of people with confirmed Covid-19 and do not apply to people who are simply quarantined after contact with an infected person.

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 contagiousness.

The study looked at key factors including viral load – how the amount of virus in the body changes throughout infection – and viral RNA shedding – how long a person loses genetic material viral.

He also looked at the isolation of the live virus – a stronger indicator of a person’s infectivity, as the live virus is isolated and tested to see if it can replicate successfully in the lab.

From these studies, the authors calculated the average duration of viral RNA shedding and examined changes in viral load and the success of isolating live virus from different samples collected throughout ‘an infection.