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expert reaction to study looking at presymptomatic SARS-CoV-2 coronavirus transmission in a nursing home in the US

A study, published in the New England Journal of Medicine, has looked at the presymptomatic transmission of SARS-CoV-2 in a nursing home in the USA.


Prof Babak Javid, Principal Investigator, Tsinghua University School of Medicine, Beijing, and Consultant in infectious diseases at Cambridge University Hospitals, said:

“The new study, yet again, suggests that approximately half of people infected with the coronavirus causing Covid do not show symptoms.  Testing only those people who present themselves to healthcare facilities risks a biased view of a disease.  At the outset of the outbreak in Wuhan, only people who had life-threatening complications from Covid were initially identified.

“A new study in the New England Journal of Medicine, looked at an outbreak of Covid in a nursing home in WA state, US.  Two thirds of the residents tested positive for coronavirus, and of those, just over half did not have any symptoms at the time of testing (although about half of those went on to develop symptoms later).

“One of the current controversies in infection control for Covid is whether people without symptoms can transmit the virus.  Here, the researchers measured the amount of virus genetic material in those testing positive, and found no difference in virus levels (‘viral load’) between patients who were symptomatic and asymptomatic.  They could also culture live virus in the laboratory from 2/3 of the samples, including 10/16 with typical symptoms, 17/24 of those that were not symptomatic at time of testing, but later developed symptoms, and 1/3 that never developed symptoms.  This suggests that presymptomatic and symptomatic patients were probably equally likely to be able to spread infection.

“The initial response to the outbreak was to isolate those residents that showed symptoms, but this failed to halt spread of Covid in the facility, strongly suggesting that spread from patients without symptoms contributed to the ongoing spread in the facility.

“The study has important implications for our understanding the transmission of Covid, and the appropriate public health measures we should take to limit spread.  It suggests focusing solely on patients with symptoms is unlikely, by itself, to halt transmission of the disease.”


Prof Trish Greenhalgh, Professor of Primary Care Health Sciences, Nuffield Department of Primary Care Health Sciences, University of Oxford, said:

“The Jernigan article describes a small study in a single nursing home, in which 48 of 76 residents tested positive for Sars-CoV-2 on nasal swabs.  Of those, 48 (56%) had no symptoms on the day they were tested, though most of those subsequently developed symptoms of covid-19.  Indeed, serial testing showed that nursing residents were shedding virus in their noses from 1 to 6 days before they developed symptoms.  Of residents who tested positive for Sars-CoV-2, more than a quarter died.  The accompanying editorial by Havir and colleagues draws two important conclusions: that if we only test symptomatic people, we will miss many cases of covid-19, and that unless the general public wear face masks when in crowded outdoor and indoor spaces whether symptomatic or not, widespread transmission of this deadly virus will continue.

“One swallow does not make a summer, but this is the eleventh cohort of asymptomatic transmission revealed by proactive testing.  As Daniel Oran and Eric Topol have shown, similar findings were found in cohorts identified for nationwide testing (Iceland), local population testing (Vo, Italy), passengers or crew of three ships (Diamond Princess, USS Theodore and Charles de Gaulle aircraft carrier), residents of two homeless shelters (Boston and Los Angeles), ex-pats (Japanese evacuated from Wuhan and Greek citizens evacuated from other countries), and pregnant women (New York City obstetric patients).  In those cohorts, between 31% and 88% were asymptomatic when tested.

“Sars-CoV-2 is extremely contagious and can be deadly.  It multiplies in the upper respiratory tract.  It has already infected almost 3 million people worldwide.  If we want to stamp it out, neither the WHO’s advice (that nobody needs to wear a mask unless symptomatic) nor the current UK government policy (that nobody should be required to wear a mask outside the home) stand up to scientific scrutiny.  As Havir et al say, “This unprecedented pandemic calls for unprecedented measures to achieve its ultimate defeat”.  Let’s start by requiring people to cover their mouths and noses when in public places where it is not possible to remain 2 metres away from other people.”


Paper: ‘Presymptomatic SARS-CoV-2 Infections and Transmission in a Skilled Nursing Facility’ by Melissa M. Arons et al. was published in the NEJM on Friday 24 April 2020.

DOI: 10.1056/NEJMoa2008457

Editorial: ‘Asymptomatic Transmission, the Achilles’ Heel of Current Strategies to Control Covid-19’ by Monica Gandhi et al. was published in the NEJM on Friday 24 April 2020.

DOI: 10.1056/NEJMe2009758


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