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COVID-19: Questions over Asymptomatic Transfer

Published: (Updated: ) in Australian News by .

As Tasmania heads into winter the jury is still out as to whether the risk of contracting COVID-19 will worsen with the cold weather. We are of course the first hemisphere to confront winter conditions during this pandemic and because of the decision by Premier Gutwein to use our unique moat, Tasmania is well placed […]

As Tasmania heads into winter the jury is still out as to whether the risk of contracting COVID-19 will worsen with the cold weather. We are of course the first hemisphere to confront winter conditions during this pandemic and because of the decision by Premier Gutwein to use our unique moat, Tasmania is well placed to face whatever winter may bring.

What has however become apparent is that asymptomatic cases of COVID-19 may be much higher than anticipated following two research studies published 28 May 2020 in JAMA Network Open and Thorax Journal. The Authors* behind the research paper published in Thorax believe this is the first instance of complete COVID-19 testing of all passengers and crew on an isolated cruise ship during the current COVID-19 pandemic.

The study reveals the majority of COVID-19 positive patients on an isolated Antarctic expedition cruise ship were asymptomatic. Of the 217 passengers and crew 128 tested positive for COVID-19, the majority of COVID-19 positive patients were asymptomatic (81%, 104 patients).

These latest research findings may well be of interest in the legal case currently being mounted against operator Princess Cruises by many of the tourists who were aboard the Ruby Princess when COVID-19 cause such havoc.

World Economic Forum

Dr Maria van Kerkhove. Image courtesy World Economic Forum.

At the World Health Organisation (WHO) press conference on Monday 8 June, Dr Maria van Kerkhove, an American infectious disease epidemiologist, stated that asymptomatic transmission of SARS-CoV-2 is rare, which has surprised a number of expert observers.

The data behind her making these comments is not yet publicly available and her statement has resulted in a reaction among experts. Her comment at the WHO’s Monday press briefing about its rarity was based on two or three studies following up the contacts of asymptomatic people, and unpublished data shared by countries or experts with her organisation.

Prof Liam Smeeth, Professor of Clinical Epidemiology, London School of Hygiene and Tropical Medicine, said:

“I was quite surprised by the WHO statement, and I have not seen the data the statement is based on.

“It goes against my impressions from the science so far that suggest asymptomatic (people who never get symptoms) and pre-symptomatic people are an important source of infection to others.

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This is the main basis for steps such as self-isolation and lockdown – steps we know, from yesterday’s two Nature papers have massively reduced the numbers of people infected and have prevented millions of deaths globally.

“What is true is that once we have successfully interrupted community transmission, our main can shift and focus on case finding and testing of symptomatic people and tracing, testing and self-isolation of their contacts.

“There remains scientific uncertainty, but asymptomatic infection could be around 30% to 50% of cases. The best scientific studies to date suggest that up to half of cases became infected from asymptomatic or pre-symptomatic people.”

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

“In the WHO’s press conference today, it was suggested that patients with asymptomatic infection rarely transmit Covid to others.  Dr van Kerkhove makes the important distinction between true asymptomatics (never develop symptoms), presymptomatics (don’t have symptoms at the time of testing positive for SARS-CoV-2 but later develop symptoms) and paucisymptomatics (have atypical or very mild symptoms).  She describes that unpublished data suggest “asymptomatics” (not further clarified) do not transmit infection.  This may well be true.  Detailed contact tracing from Taiwan as well as the first European transmission chain in Germany suggested that true asymptomatics rarely transmit.

“However, those (and many other) studies have found that paucisymptomatic transmission can occur, and in particular, in the German study, they found that transmission often appeared to occur before or on the day symptoms first appeared (i.e. presymptomatic transmission).

“Without having access to the data Dr van Kerkhove refers to, it is difficult to make any other assessment.  I’m sure those data will become publicly available in due course.  In the meantime, other data available, from studies in several continents confirming that presymptomatic transmission does occur would suggest that being well does not necessarily mean one cannot transmit SARS-CoV-2.  However, the important point is made that some even very mild symptoms that are not ‘typical’ of Covid (i.e. not having a fever or cough) may still represent someone who can be contagious.  This has important implications for the track/trace/isolate measures being instituted in many countries.”

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What is apparent is this rapidly evolving pandemic is raising more questions, not the least being this is not over by a long shot and it is not necessarily people showing outward symptoms that are the carriers. This strongly suggests social distancing and isolation is the best strategy thus far until more is known about COVID-19.

When approached, the Tasmanian Department of Health declined to comment on the question of asymptomatic transfer.

Professor Raina MacIntyre

Professor Raina MacIntyre is Head of the Biosecurity Program at the Kirby Institute at the University of NSW and is an expert in influenza and emerging infectious diseases.

“These studies add to an already substantial body of evidence that asymptomatic and presymptomatic infection is common with COVID-19. Studies of the Diamond Princess found about two-thirds of passengers were infected, with a high proportion asymptomatic.

Studies in aged care and other outbreaks have also found 50 per cent or more of all positive cases are asymptomatic.

“We should not be debating this any longer.

High-risk contacts in outbreak situations, whether family contacts or in a closed setting outbreak, should be tested regardless of symptoms or cases will be missed.

*****     *****     *****     *****     *****

The Greg Mortimer Antarctic Expedition

Antarctic cruise ship

Image courtesy Unsplash.

The Antarctic expedition cruise ship departed from Ushuaia, Argentina mid-March 2020, after the global COVID-19 pandemic was declared by the WHO, with all 128 passengers and 95 crew screened for COVID-19 symptoms, and body temperatures taken before boarding.

All passengers and crew had regular body temperature reviews performed by the ship’s two physicians and all were well, until the first recorded fever on board the ship was a febrile passenger on day 8. Isolation protocols were immediately commenced, with all passengers confined to cabins and surgical masks issued to all.

Full personal protective equipment was used for any contact with any febrile patients, and N95 masks were worn for any contact with passengers in their cabins.

The crew still performed duties, including meal services to the cabin doors three times a day, but rooms were not serviced. Expedition staff helped with crew duties at meal service

“We conclude that the prevalence of COVID-19 on affected cruise ships is likely to be significantly underestimated, and strategies are needed to assess and monitor all passengers to prevent community transmission after disembarkation.”

No passengers or crew that had transited through China, Macau, Hong Kong, Taiwan, Japan, South Korea or Iran in the previous 3 weeks were permitted to board, given that these countries were where COVID-19 infection was most prevalent at the time. Multiple hand hygiene stations were positioned throughout the ship and especially in the dining area.

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Further fevers were detected in three crew on day 10, two passengers and one crew on day 11, and three passengers on day 12.

From the departure date in mid-March 2020 and for the next 28 days, the expedition cruise ship had no outside human contact and was thus a totally isolated environment in this sense.

Despite 128 (59%) of the population testing positive, fever and mild symptoms were present in only 16 of 128 COVID-19-positive patients (12.5%), with another 8 medically evacuated and 4 requiring intubation and ventilation. There has unfortunately been one death to date (0.8%). There were therefore a total of 24 COVID-19-positive patients who were symptomatic (19%), with the majority being asymptomatic (104 patients or 81%).

The authors conclude from this observational study that:

Alvin J Ing, Faculty of Medicine, Health and Human Sciences, Macquarie University, Sydney, New South Wales, Australia
Christine Cocks, Oncology Trials Unit, Sunshine Coast University Hospital, Sunshine Coast, Queensland, Australia
Jeffery Peter Green, Royal Australian College of General Practitioners, East Melbourne, Victoria, Australia

Thorax is one of the world’s leading respiratory medicine journals, publishing clinical and experimental research articles on respiratory medicine, paediatrics, immunology, pharmacology, pathology, and surgery.

TASMANIAN TIMES: How Common is Asymptomatic COVID-19?

Source: Tasmanian Times

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