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What Does an Asymptomatic COVID-19 Infection Look Like?


What Does an Asymptomatic COVID-19 Infection Look Like?

Some people who get sick with COVID-19 don't feel any symptoms of the disease, but what does an asymptomatic COVID-19 infection look like?

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COVID-19 Insights: Are There Asymptomatic COVID-19 Patients?

Asymptomatic Cases of SARS-COV-2

Asymptomatic kids
Clinical and epidemiological features of 36 children with coronavirus disease 2019 (COVID-19) in Zhejiang, China: an observational cohort study

36 children. All were identified to be infected with severe acute respiratory syndrome coronavirus 2

Asymptomatic (ten [28%]) or
had acute upper respiratory symptoms (seven [19%]).

COVID-19 Antibody Seroprevalence in Santa Clara County, California

Their disclaimer
This article is a preprint and has not been certified by peer review [what does this mean?]. It reports new medical research that has yet to be evaluated and so should not be used to guide clinical practice.

Total population of the county is 1.9M

On the sample date 3rd and 4th of April, confirmed coronavirus cases in Santa Clara County was around 1,100. This is 0.05% of the population

Tested antibodies to SARS-COV-2 in the serum.
3,330 people
The population prevalence of COVID-19 in Santa Clara ranged from 2.49% (95CI 1.80-3.17%) to 4.16% (2.58-5.70%).
These prevalence estimates represent a range between 48,000 and 81,000 people infected in Santa Clara County by early April
50-85-fold more than the number of confirmed cases.

Coronavirus spread: Number of people infected by COVID-19 may be 50-80 times higher than official count, Stanford study suggests


healthy/asymptomatic cases
NIH begins study to quantify undetected cases of coronavirus infection

SARS-COV-2 Antibody tests begin for understanding the seroconversion in

UC Berkeley to test 5,000 healthy people in East Bay for coronavirus

Over eight months, the researchers will conduct rounds of diagnostic tests using nasal swabs to identify infections. And they will take saliva and blood samples to look for antibodies, which would indicate that such people had had COVID-19 and recovered — perhaps without ever realizing they’d been infected with the coronavirus.

Presymptomatic Transmission of SARS-CoV-2 — Singapore, January 23–March 16, 2020

Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility — King County, Washington, March 2020

You May Be Infected With Coronavirus and Not Know It

25% of the infected may be asymptomatic

CDC Director On Models For The Months To Come: 'This Virus Is Going To Be With Us'

I have been saying this for a long time.

1 in 4 people can be asymptomatic

One of the [pieces of] information that we have pretty much confirmed now is that a significant number of individuals that are infected actually remain asymptomatic. That may be as many as 25%. That's important, because now you have individuals that may not have any symptoms that can contribute to transmission, and we have learned that in fact they do contribute to transmission.
And finally, of those of us that get symptomatic, it appears that we're shedding significant virus in our oropharyngeal compartment, probably up to 48 hours before we show symptoms. This helps explain how rapidly this virus continues to spread across the country, because we have asymptomatic transmitters and we have individuals who are transmitting 48 hours before they become symptomatic.

Pediatrician says 80% of kids likely have coronavirus, but they're so asymptomatic you'd never know

Children are asymptomatic, mildly symptomatic, or note tested. But they are spreading the virus.

Can Asymptomatic Coronavirus Cases Be Transmitted?

A lot of people infected with the coronavirus have very mild or even no symptoms, or ones that don’t match the usual markers of fever, dry cough or difficulty breathing. The discovery of larger numbers of so-called asymptomatic cases, initially thought to be rare, underscores a key challenge in stopping the pandemic: If people don’t know they’re infected, they’re probably not taking steps to prevent transmitting it.

Peak concentration of the coronavirus in the upper airway seems to occur around the time an infected person develops symptoms. That’s usually when a person is most contagious -- coughing, sneezing or otherwise shedding virus. With this virus, however, a carrier is also capable of transmitting it even before getting the tell-tale signs of infection, as some early studies from China, Germany and Singapore indicated. And some people with the virus never feel ill, yet have been implicated in its spread. The extent to which these “silent carriers” may also be “silent spreaders” isn’t clear. It’s difficult to pinpoint the source of an individual infection, especially as the virus becomes entrenched in communities. Researchers at the University of Oxford estimated in March that a third to a half of transmissions occur from pre-symptomatic people.

The number of asymptomatic cases is “significant,” U.K. doctors wrote in a letter to the Lancet medical journal published April 16. A lack of resources for testing in many places, at least in the initial weeks of the pandemic, meant screening has focused on sick people displaying classical symptoms of Covid-19, as the disease is called. When health authorities have widened their testing, they typically find many more positive results than they had assumed. A study of cases aboard the Diamond Princess cruise ship, which docked in Japan, found that 328 of the 634, or 52%, of people who tested positive had no obvious symptoms at the time of testing. A retrospective analysis found that 10 of 43 of those asymptomatic cases did develop symptoms over a 15-day period. Testing in China, the Netherlands and Iceland, on board a U.S. aircraft carrier and among obstetric patients in New York City, found anywhere from 43% to 88% of people testing positive were asymptomatic at the time.

Data from China indicate that at least a fifth of patients who have no signs of Covid-19 at the time of testing positive are incubating the disease and do develop symptoms days later. Some people with the coronavirus develop atypical symptoms -- ones that don’t meet the definitions health authorities use to identify likely cases. These signs include diarrhea and the abrupt loss of smell and taste. That’s a big change from back in February when a joint World Health Organization-China mission concluded that asymptomatic infection “appears to be relatively rare.” The WHO said in April that the risk of catching Covid-19 from someone with no symptoms at all is “very low,” though it’s possible it could be caught from the mild cough of someone who doesn’t feel ill.

Some researchers have suggested that unrecognized carriers may be a reason why this coronavirus has spread extremely quickly relative to others, such as the one responsible for severe acute respiratory syndrome, or SARS, almost 20 years ago. Current containment measures are predicated on early detection and isolation, but patients with mild, non-specific, or no symptoms are more difficult to identify. Such cases can also increase the risk to health-care workers if a patient undergoes certain high-risk medical or surgical procedures, such as a colonoscopy. Fourteen hospital staff were infected after a patient in China tested positive days after surgery, and they had failed to take necessary infection-control precautions.

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Infectious Disease Specialist on Asymptomatic COVID Patients and the Spread of the Virus

Dr. Henry Anyimadu, Infectious Disease Specialist at Hartford HealthCare, joins Channel 8 to discuss COVID patients with no symptoms and how that may relate to the spread of the virus.

Asymptomatic infection

COVID-19: What proportion are asymptomatic?

Between 5% and 80% of people testing positive for SARS-CoV-2 may be asymptomatic

Symptom-based screening will miss cases, perhaps a lot of them

Some asymptomatic cases will become symptomatic over the next week (i.e. pre-symptomatic)

Children and young adults can be asymptomatic

There is not a single reliable study to determine the number of asymptotics

Population based antibody testing required

Diamond Princess

3,711 people tested
634 tested positive


Vo’Euganeo, (50Km west of Venice)

All 3,000 people in village tested

50 – 75% asymptomatic

Asymptomatics infectious
represented ‘a formidable source’ of contagion

328 adults in Shanghai

328 adults were diagnosed with COVID-19 in Shanghai

Among them, 13 patients were asymptomatic at time of diagnosis

No subjective symptoms 2 weeks before admission

All of the 13 (4%) them were close contacts of the confirmed cases

Japanese nationals evacuated from Wuhan

565 citizens had been evacuated
30.8% (7.7– 53.8%).
30 days after evacuation

Asymptomatic and Pre-symptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility - King County, Washington

CDC 76 residents

categorized as asymptomatic or symptomatic at the time of testing and for previous 14 days

23 (30%) residents, antigen positive and symptomatic
13 (57%) were asymptomatic

10 of these 13 previously asymptomatic residents developed symptoms within 7 days

Therefore 3 (4%) out of 76 truly asymptomatic

RT-PCR) values indicated large quantities of viral RNA in asymptomatic, pre-symptomatic, and symptomatic residents

Symptom based screening on a particular day could fail to detect half of positive cases


Population screening, 57% symptomatic, 43% asymptomatic

CDC, Interim Clinical Guidance for Management of Patients with Confirmed Coronavirus Disease (COVID-19)

13% of positive children asymptomatic

Risk of transmission is thought to be greatest when patients are symptomatic since viral shedding is greatest at the time of symptom onset and declines over the course of several days to weeks.

81% of infections show mild symptoms
14% exhibit severe symptoms
5% fall critically ill

Asymptomatic coronavirus infection: MERS-CoV and SARS-CoV-2 (COVID-19)

The extent of asymptomatic MERS-CoV (2012) cases is about 9.8%

How much is covid-19 spreading via asymptomatic versus symptomatic infections? (4th May)

Mathematical models SEIIR

Infected, symptomatic
Infected, asymptomatic
Therefore, need widespread antibody testing and contact tracing as soon as possible.

WHO Says Covid-19 Asymptomatic Transmission Is ‘Very Rare’

Jun.08 -- Maria Van Kerkhove, head of the World Health Organization’s emerging diseases and zoonosis unit, says transmission of the coronavirus by people who aren’t showing symptoms is very rare.” She spoke Monday at a briefing in Geneva. (Excerpt)

Studying COVID-19 in asymptomatic people

Researchers at IU School of Medicine are studying how COVID-19 might be transmitted by asymptomatic people to learn how to slow the spread of the virus. Read more about the study at

The threat of coronavirus transmission by asymptomatic carriers | COVID 19

Asymtomatic coronavirus spreaders dont show visible symptoms, like coughing or fever. But they could well be passing on the coronavirus. Experts argue many patients appear most contagious right before the onset of symptoms. Models suggest half all transmissions can be traced back to people, before they get sick - if they get sick at all. Many doctors say therefore only mass testing can break the chain of transmission. But the US Centers for Disease Control and Prevention has changed its testing guidelines to exclude people who don't have symptoms, even if they've been recently exposed to the virus.

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#Coronavirus #Contagion #Asymtomatic

Can coronavirus be spread by people with no symptoms?

As the coronavirus outbreak continues, people are asking if it can be spread by someone who isn't showing symptoms. It's been a controversial question ever since a report in the New England Journal of Medicine claimed an asymptomatic woman triggered a chain of infections near Munich. Infectious disease specialist Dr. Isaac Bogoch explains how the report got it wrong.

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WHO advice says asymptomatic COVID-19 patients 'very rarely' spread virus

Professor Karol Sikora, a former WHO expert, reacts to the news that according to the World Health Organisation people without COVID-19 symptoms but who have the disease are not likely to spread the virus. This goes against the previous idea that super-spreaders of people without symptoms could spread the virus.

Read more: Asymptomatic coronavirus patients ‘very rarely’ spread disease, says WHO in ‘significant development’ -

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Clearing confusion on asymptomatic spread of COVID-19

Confusion abounds about the difference between asymptomatic and pre-symptomatic infections when it comes to the pandemic coronavirus. Dr. John Lynch, medical director of infection prevention and control at Harborview, explains asymptomatic means someone doesn't show symptoms the entire time they have this coronavirus in their body.

Pre-symptomatic describes the period of time before someone develops signs of illness. But, whether someone is asymptomatic or presymptomatic doesn't really matter to the general public. Either way, anyone carrying the coronavirus can spread the disease.

I think what we really want to send home is that you can have no symptoms, feel well and transmit this virus to other people, Lynch says.

That's why the practices of wearing a mask, washing your hands, and physical distancing are so important to prevent the spread of COVID-19.

Answer Bank: Am I an asymptomatic COVID-19 patient?

As the COVID-19 pandemic continues to develop in nearly every country, the risk of asymptomatic patients has been brought into sharp focus. So, what are asymptomatic patients and how are they identified? CGTN explains.

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#askHKUMed on COVID-19: Will asymptomatic virus carriers forever carry the virus?


#askHKUMed are asymptomatic virus carriers will eventually become sick and recover, or just forever be carriers?

Professor John Nicholls
Clinical Professor
Department of Pathology
LKS Faculty of Medicine, The University of Hong Kong

What we know about the risk of asymptomatic spread of coronavirus

The World Health Organization is walking back a comment suggesting that the spread of COVID-19 from an asymptomatic person is rare. Dr. Ashish K. Jha, director of the Harvard Global Health Institute, joins CBSN to discuss when patients are the most contagious, and a new Harvard Medical School study which suggests the coronavirus may have been in China as early as August.

130 new cases of asymptomatic COVID-19 infections in China

China has reported 130 new cases of COVID-19 in people who do not display any symptoms. It is the first time the national tally is taking into account asymptomatic infections. Fears are rising that China could see a third wave of coronavirus infections as lockdowns across Hubei province are lifted.

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What about asymptomatic people spreading COVID-19?

Experts discuss what the current thoughts are around virus being spread before symptoms and share best practices to follow.

Dr. Gilaad Kaplan (MD, MPH, FRCPC), Associate Professor and Gastroenterologist, Director of the Environmental Health Research Group, Snyder Institute for Chronic Diseases and Institute of Public Health, Departments of Medicine and Community Health Sciences at the University of Calgary

Dr. Lisa Barrett (MD, PhD., FRCPC), Assistant Professor and Clinician Scientist, Nova Scotia Health Authority, Divisions of Infectious Diseases, Microbiology and Immunology at Dalhousie University

Facts Not Fear: Why are some people with COVID-19 asymptomatic?

9Health Expert Dr. Payal Kohli is talking about the scientific factors that offer insight into how sick people get.

How long can asymptomatic people carry COVID-19? Your coronavirus questions answered

You have a lot of questions about the COVID-19 pandemic and we're doing our best to get answers for you during our 7 p.m. newscast. You can text your questions to 503-226-5111 or email us at More questions answered:

COVID-19: How many asymptomatic people could be walking around?

Doctors answer your questions about the coronavirus, including if there’s any way of knowing how many asymptomatic people could be walking around when only symptomatic people are being tested.

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What to do if you are asymptomatic with COVID-19

Dr. Yvens Laborde, Ochsner Medical Director of Global Health, discusses what you should do if you've tested positive for COVID-19 but aren't sick.



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