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Asymptomatic patients may account for as much as 45 per cent of all Covid-19 cases, playing a significant role in the early and ongoing spread of the novel coronavirus, according to a new research.
The study, published in the journal Annals of Internal Medicine, suggests that an extraordinary percentage of people infected by the ongoing deadly Covid-19 pandemic never showed symptoms of the disease.
The report highlights the need for expansive testing and contacts tracing to mitigate the pandemic.
"The silent spread of the virus makes it all the more challenging to control," said study researcher Eric Topol from the Scripps Research Translational Institute in the US.
"Our review really highlights the importance of testing. It's clear that with such a high asymptomatic rate, we need to cast a very wide net, otherwise the virus will continue to evade us," Topol added.
For the results, the research team collected information from testing studies on 16 diverse cohorts from around the world.
These datasets -- gathered via keyword searches of non peer-reviewed research portals PubMed, bioRxiv and medRxiv, as well as Google searches of relevant news reports -- included data on nursing home residents, cruise ship passengers, prison inmates and various other groups.
What virtually all of them had in common was that a very large proportion of infected individuals had no symptoms, the researchers said.
Among more than 3,000 prison inmates in four states who tested positive for the coronavirus, the figure was astronomical: 96 per cent asymptomatic, according to the study.
The review further suggests that asymptomatic individuals are able to transmit the virus for an extended period of time, perhaps longer than 14 days.
The viral loads are very similar in people with or without symptoms, but it remains unclear whether their infectiousness is of the same magnitude.
To resolve that issue, we'll need large-scale studies that include sufficient numbers of asymptomatic people.
The authors also conclude that the absence of symptoms may not imply an absence of harm.
CT scans conducted on 54 per cent of 76 asymptomatic individuals on the Diamond Princess cruise ship, appear to show significant subclinical lung abnormalities raising the possibility of SARS-CoV-2 infection impacting lung function that might not be immediately apparent.
The scientists said that further research is needed to confirm the potential significance of this finding.
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