Coronavirus is MOST infectious in the five days after symptoms

Coronavirus is MOST infectious in the five days after symptoms first appear, study suggests – highlighting the need to isolate cases early

  • Review of 98 studies looked at the amount of coronavirus found in airways 
  • Study reveals SARS-CoV-2 peaks within five days of symptom onset 
  • This is when a patient is believed to be most infectious due to the high viral load   

The five days after a coronavirus-infected individual develops symptoms are when they are at their most infectious, a study has revealed. 

Research from Dr Muge Cevik at the University of St Andrews also found no live virus in samples taken more than nine days after symptom onset.

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

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

Experts collated and scrutinised 98 papers to inform their conclusions.  

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The five days after a coronavirus-infected individual develops symptoms are when they are at their most infectious, a study has revealed (stock)

The researchers assessed how much SARS-CoV-2 was detected between the mouth and the lungs at various time intervals. 

As well as looking at the behaviour of SARS-CoV-2, the researchers also assessed two related coronaviruses, MERS and SARS.  

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

It found that the level of virus causing the current pandemic is highest at the time symptoms begin, or before day five of symptoms. 

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

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

‘It provides a clear explanation for why Sars-CoV-2 spreads more efficiently than Sars-CoV and Mers-CoV and is so much more difficult to contain.

Covid-19 causes DELIRIUM in one in three elderly patients 

Delirium is a common symptom of coronavirus in elderly patients, found in around one in three infected over-65s.  

Researchers say delirium can be particularly detrimental to elderly people, increasing their likelihood of severe disease and death. 

The US-wide study looked at 817 older patients who tested positive for the coronavirus, 226 (28 per cent) of whom were diagnosed with delirium. 

The cohort had an average age of 78, and 84 (37 per cent) of the delirious patients did not have any typical Covid symptoms — such as a fever or shortness of breath.

Eighty-four delirious patients died in hospital, and scientists say delirium increases the risk of death by 24 per cent and likelihood of ICU admission by 67 per cent. 

‘Our findings are in line with contact tracing studies which suggest the majority of 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 start.

‘We also need to raise public awareness about the range of symptoms linked with the disease, including mild symptoms that may occur earlier on in the course of the infection than those that are more prominent like cough or fever.’  

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

Researchers said the results are only relevant for the period of self-isolation for people with confirmed Covid-19, and do not apply to people simply quarantining after contact with someone infected.

Many countries recommend that people with the virus should self-isolate for 10 days, which the authors said is in line with their findings, cautiously covering the period of infectiousness.  

The study looked at key factors including viral load – how the amount of the virus in the body changes throughout infection – and viral RNA shedding – the length of time someone sheds viral genetic material.

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

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

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