Covid-19: four fifths of cases are asymptomatic, China figures indicate

The British Medical Journal published an article on April 2nd, parts of which are published below. The full article is available on the BMJ website and is fully referenced.

BMJ 2020; 369 doi: (Published 02 April 2020)Cite this as: BMJ 2020;369:m1375

New evidence has emerged from China indicating that the large majority of coronavirus infections do not result in symptoms.

Chinese authorities began publishing daily figures on 1 April on the number of new coronavirus cases that are asymptomatic, with the first day’s figures suggesting that around four in five coronavirus infections caused no illness. Many experts believe that unnoticed, asymptomatic cases of coronavirus infection could be an important source of contagion.

A total of 130 of 166 new infections (78%) identified in the 24 hours to the afternoon of Wednesday 1 April were asymptomatic, said China’s National Health Commission. And most of the 36 cases in which patients showed symptoms involved arrivals from overseas, down from 48 the previous day, the commission said.

China is rigorously testing arrivals from overseas for fear of importing a fresh outbreak of covid-19.

In an article on the website of the Centre for Evidence-Based Medicine, Jefferson and Carl Heneghan, director of the centre and editor of BMJ EBM, write, “There can be little doubt that covid-19 may be far more widely distributed than some may believe. Lockdown is going to bankrupt all of us and our descendants and is unlikely at this point to slow or halt viral circulation as the genie is out of the bottle. “What the current situation boils down to is this: is economic meltdown a price worth paying to halt or delay what is already amongst us?”

Responses to the article are also very interesting. A retired Medical Director from Inverness postulates that one reason why there are so many asymptomatic carriers is that they may have been infected via the eyes rather than the respiratory route via nose and mouth.

“Coronavirus has shown remarkable variability in its effects, ranging all the way from asymptomatic carriers to viral pneumonitis and death. The three routes of infection are reckoned to be via the mouth, nose and eye mucosa.

Asymptomatic infection
I have not heard of any significant local symptoms associated with infection via the eye mucosa and this route of infection may account for the large proportion of asymptomatic infections. It may also be the route through which the herd immunity that is surely building up in the community has developed. Local eye inoculation may have provoked an immune response before there was significant involvement of the respiratory mucosa.

These different routes of infection may suggest that mouth breathing is more likely to lead to viral pneumonitis than nasal breathing, and that face masks, scarves and bandanas in the community may direct any viral particles towards the eyes rather than the nose and mouth.

Researchers could investigate whether the severe respiratory cases are predominantly mouth-breathers and whether eye inoculation has been the route for asymptomatic infection.”

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