The threat of asymptomatic cases of coronavirus

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The novel nature of the SARS-CoV-2 virus means there are insurmountable unknowns about the new coronavirus disease.

As China relaxes lockdown measures and people return to work, there are concerns around the possibility that asymptomatic could continue to spread the virus.

Experts say it will take many months, or potentially years to understand all of the fundamental details about COVID-19. Preliminary conclusions are being made and broadcast almost daily, but questions on how the virus is transmitted, if it mutates a lot or a little, and how the body generates immunity and for how long - all remains to a large extent, unknown.

Asymptomatic coronavirus cases

Asymptomatic cases of coronavirus are defined as individuals who test positive for the virus without displaying symptoms such as fever, cough and sore throat that are self-noticeable or identifiable clinically, states the National Health Commission (China). Some of those cases will develop symptoms over a 14-day incubation period, while others will remain symptom-free. 

It is unknown what portion of adults with COVID-19 are asymptomatic.

China has however begun to release data regarding confirmed cases of asymptomatic coronavirus, as of April 1.

The primary issue with asymptomatic coronavirus cases is that evidence is scarce and confusing. 

Experts currently believe that in order to contain the further spread of COVID-19, asymptomatic patients, along with those in contact with them, should be quarantined for 14 days, which should prevent against reinfection or chance of a second wave of epidemic in a country - but evidence surrounding this remains inconclusive. 

Coronavirus testing

There are new fears in China that new cases of coronavirus from those travelling from outside the country could spark a new extensive outbreak. In an attempt to counteract this threat, international travellers are being rigorously tested. Recent results from this testing procedure was released by China’s National Health Commission - identifying as of April 1 - 166 new cases of infection, with 130 defined as “asymptomatic”. 

"The sample is very small, but more data should soon be available. Also, it’s not clear exactly how these cases were identified. But let’s just say it can be generalised. Even if the data is 10% or so out, this still suggests the virus is everywhere." said Tom Jefferson epidemiologist and honorary researcher at the Centre for Evidence-Based Medicine at the University of Oxford in an interview for the medical journal BMJ.

Jefferson believes that this testing programme demonstrates a high likelihood that the virus has been circulating among populations for much longer than previously thought.

An isolated Italian village located 50 kilometres outside of Venice started to test all 3,000 of its inhabitants in mid-February. Sergio Romagnani, a researcher at the University of Florence, followed the whole process and found that the vast majority of cases detected (between 50 and 75%) were asymptomatic. If the inhabitants tested positive for COVID-19, they were placed in strict isolation. After just ten days of his process, it is understood that cases of coronavirus dropped by 90% in the small village.

Coronavirus testing in countries including Iceland and South Korea have also identified a high proportion of detected cases as having no recognisable symptoms, raising concern that the number of silent carriers may be greater than previously thought.

Just over 5% of Iceland’s population have been tested, with data suggesting around half of the confirmed cases showed no clear symptoms. 

Increasing evidence suggests that a significant portion of COVID-19 patients may never show coronavirus symptoms at all, meaning it is ever more essential to follow health and hygiene instructions outlined by the WHO - on a consistent and strict basis. 

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