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People who contract the novel coronavirus emit high amounts of virus very early on in their infection, according to a new study from Germany that helps to explain the rapid and efficient way in which the virus has spread around the world.

At the same time, the study suggests that while people with mild infections can still test positive by throat swabs for days and even weeks after their illness, those who are only mildly sick are likely not still infectious by about 10 days after they start to experience symptoms.

The study, by scientists in Berlin and Munich, is one of the first outside China to look at clinical data from patients who have been diagnosed with Covid-19, the disease caused by the coronavirus, and one of the first to try to map when people infected with the virus can infect others.


It was published Monday on a preprint server, meaning it has not yet been peer-reviewed, but it could still provide key information that the public health response has been lacking.

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“This is a very important contribution to understanding both the natural history of Covid-19 clinical disease as well as the public health implications of viral shedding,” said Michael Osterholm, director of the University of Minnesota’s Center for Infectious Diseases Research and Policy.


The researchers monitored the viral shedding of nine people infected with the virus. In addition to tests looking for fragments of the virus’s RNA, they also tried to grow viruses from sputum, blood, urine, and stool samples taken from the patients. The latter type of testing — trying to grow viruses — is critical in the quest to determine how people infect one another and how long an infected person poses a risk to others.

Importantly, the scientists could not grow viruses from throat swabs or sputum specimens after day 8 of illness from people who had mild infections.

“Based on the present findings, early discharge with ensuing home isolation could be chosen for patients who are beyond day 10 of symptoms with less than 100,000 viral RNA copies per ml of sputum,” the authors said, suggesting that at that point “there is little residual risk of infectivity, based on cell culture.”

Public health officials and hospitals have been trying to make sense of patients who seem to have recovered from Covid-19 but who still test positive for the virus based in throat swabs and sputum samples. In some cases, people test positive for weeks after recovery, the World Health Organization has noted.

Those tests are conducted using PCR — polymerase chain reaction — which looks for tiny sections of the RNA of the virus. That type of test can indicate whether a patient is still shedding viral debris, but cannot indicate whether the person is still infectious.

The researchers found very high levels of virus emitted from the throat of patients from the earliest point in their illness —when people are generally still going about their daily routines. Viral shedding dropped after day 5 in all but two of the patients, who had more serious illness. The two, who developed early signs of pneumonia, continued to shed high levels of virus from the throat until about day 10 or 11.

This pattern of virus shedding is a marked departure from what was seen with the SARS coronavirus, which ignited an outbreak in 2002-2003. With that disease, peak shedding of virus occurred later, when the virus had moved into the deep lungs.

Shedding from the upper airways early in infection makes for a virus that is much harder to contain. The scientists said at peak shedding, people with Covid-19 are emitting more than 1,000 times more virus than was emitted during peak shedding of SARS infection, a fact that likely explains the rapid spread of the virus. The SARS outbreak was contained after about 8,000 cases; the global count of confirmed Covid-19 cases has already topped 110,000.

Osterholm said the data in the paper confirm what the spread of the disease has been signaling — “early and potentially highly efficient transmission of the virus occurs before clinical symptoms or in conjunction with the very first mild symptoms.”

The study also looked at whether people who have been infected shed infectious virus in their stool. The report of last month’s international mission to China — co-led by the WHO and China — said that in several case studies in China, “viable virus” had been recovered from stool but that isn’t likely driving transmission of the virus.

The German researchers found high levels of viral fragments in 13 stool samples from four patients in their study, but they were unable to grow virus from any of them. The paper noted, though, that all the patients had mild illness, and the fact that they could not find virus in their stool doesn’t rule out that it could happen in other cases.

“Further studies should therefore address whether SARS-CoV-2 shed in stool is rendered non-infectious though contact with the gut environment,” they wrote, adding that their findings suggest measures to try to stop spread of the virus should focus on respiratory tract transmission — protecting others from the coughs and sneezes of people infected with the virus.

Virus could not be grown from blood or urine samples taken from the patients, the authors reported.

The study also noted that people who are infected begin to develop antibodies to the virus quickly, typically within six to 12 days. The rapid rise of antibodies may explain why about 80% of people infected with the virus do not develop severe disease.

  • seems like a lot of useful information (small data base though)…..may give some basis for optimism that a 14 day quarantine would do more than just slow the spread.
    thank you

  • Re:using antibodies (Pamela’s comment). I don’t think you are explaining this idea correctly. Read the other stat news article at:

    It clearly explains that this is only of possible use for people who already have coronavirus, it does not stop people from getting the illness. Also, it is potentially harmful if given at the wrong time or wrong dose. Even at it’s most effective this type of treatment only helped about 50% of the infected people treated with antibodies during the Spanish flu (1918). China is apparently trying to use something like this, but there is no real data yet on how well it works.

    We don’t have enough test kits to find out who has had covid-19 and recovered, we can’t even test all the people who are actively sick right now! This is not a good approach for our current situation. Once we’ve got the crisis under control and plenty of kits to test, investing in this type of effort would make a lot of sense until a true vaccine can be developed though!

    • I read an article just a few moments ago (Navy Times if I recall correctly) that over a million test kits have shipped in the US in early March. The shortage of test kits may be rapidly coming to an end (hopefully).

  • do patients who have died (from Coronavirus) transmit the virus?
    I attend to the deceased and prepare them for the funeral (wash them and dress them in shrouds) are they still highly infectious?

    • Just got through reading countless published papers and unpublished papers the past few days. I recall in one of the papers that the hospitalist had a fecal sample from a deceased individual which tested positive still.

      All in all, it depends on the time the person was first infected with the virus, as the viral shedding/load is the highest at the early stages up to day 8 after infection, by day 15 after being infected the viral load decreases to almost zero. The people who are dying from this infection are dying from secondary infections like Pneumonia. While Acute Respiratory Distress Syndrome is being frequently cited as in the name SARS, that can be managed with Vents, the secondary Pneumonias can inevitably be deadlier especially in that vulnerable population.

      Long story short, if dealing with the deceased, they may still have some viral load in secretions/excrement.

  • One would say statically numbers are off since many mild and even regular cases are going unreported (untested).

    • Would have to agree 100%, since there are also many documented cases of doctors initially sending people with the “flu” and then finding out later some had covid, how many were missed.???

  • The first two paragraphs are confusing. There are too many contradictions in three to four sentences.

    • I don’t understand why you are confused. There are no contradictions in the first paragraphs. Each consecutive sentence gives more information, none of it contradictory.

  • What if someone thinks they HAD the virus already in mid February? Is there any kind of testing to see if you have built up some immunity to the virus? To ascertain that you already contracted the virus?

    • There is a test for the anti-body serum aspect of your blood. They are doing it at universities who do research, ie. Johns Hopkins in Baltimore. Also in China. China has already instituted this method to contain the virus but has had a population of 77,000 people who have had the corona virus and survived it. They are carrying the anti-bodies and are largely innocculating the most vulnerable in their population. The have beat the ‘curb’ and their death rates and confirmed cases are falling. This method will be introduced in the US in a weeks’ time. You could say just in time as things are looking pretty on edge in terms of closing down the society not to mention the effect on the stock market. But that is beside the point, apparently China got out ahead of the ball and it has worked. The method was discovered in the 1890’s and it still works when all else has failed, or will take too long, ie. a vaccine, that you can sell the company stocks for the DOW. Better to use the tried and true method from the science that we know and curb the number of deaths and cases while we still have our grandparents and children.

    • This is what I want to know. I know a lot of people, my family included, that were really sick in January. We all just assumed we had a bad cold. If this started in November, why isn’t it possible that millions of americans have already had this and just wrote it off as a cold, and maybe we are way farther along this curve than we think

    • Same, so last Monday out of nowhere I felt nauseous and immediately spiked an incredibly high fever, followed by intense painful body aches and pains in my hip bones that were so brutal I could not stand-this lasted 9 hours at which point I thought I needed medical attention- my friend an MD dropped advil off for me and advised me to take 4- I fell asleep, woke up one hour later relieved of all symptoms- like it never even happened I could stand, walk and open my eyes- fever gone I am still not sure what it was but it was so severe and then over, so if I had it am I now immune? Hoping so but don’t want to expose to others it was 8 days ago

  • Is the public being lied too? It doesn’t make sense that everything would be shut down when other viruses has killed more people than this virus. Since I’m in the vulnerable group, over 65 with compromised immune system, I’m feeling less and less safe.

  • Once someone has been infected, are they able to be reinfected or are our bodies creating the natural antibodies from the initial infection?

  • Gargles with hydrogen peroxide can help get rid of viruses. Also, nasal wash with sodium bicarbonate or baking soda helps.

  • My understanding is that the current test for SARS-CoV-2 is the RT-PCR for viral RNA detection. Since we do not know the spread of infection in the general population, a person coming in to be tested could, in fact be recovering from infection. Assuming that antibody titre would be high in such and individual, would it be better to also screen for antibody titre at the same time? Is this being done?

    • I agree. If a person has a significant antibody titre, then he/she is probably later in the course of the infection, likely not to be contagious and therefore capable of being released from quarantine earlier to return to gainful activity.

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