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It was published Monday on a preprint server, meaning it has not yet been peer-reviewed, but it could still provide key information that the public health response has been lacking.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

  • My wife, my son, and I also wonder if we were infected with this. We were each sick during early February with these same symptoms, that started out in the sinuses, moved to the throat for a couple of days and then progressed into our lungs. Our symptoms lasted about 10 days. My wife tested negative for the flu, but was diagnosed with “an unknown respiratory virus”.

  • I was also wondering, I live in Los Angeles and worked in an office full of sick people coughing from oct-feb when I finally quit after getting diagnosed with flu then pre-bronchitis/pneumonia, thought I might get this also if I stayed there. Maybe this has been going around for longer than we know.

    • I do believe also that this virus has been going on for longer than what they think. My son in Atlanta Georgia came down with the same same symptoms and December.Over short. Of time at his work pretty much everybody in his section was sick. my son was tested for flu which you did not have.

  • Just to shed more light on the value of this article, here is my own experience:

    I was in Wuhan, China on November 13-14, before China had announced the presence of the Corona Virus. My wife and I, from San Diego, aged 67 and 72 years respectively, were there in Wuhan to board our Viking Cruise on the Yangtze River on day 3 of our Undiscovered China 23-day vacation of a lifetime. On 11/22, I began having the most extreme sore throat I had ever had, followed over the next few days by sinusitis, bronchitis, and then on 11/25 pneumonia that caused the most voluminous mucous-producing cough I’ve ever had. I suspected it was streptococcal, and fortunately I had gotten a prescription for antibiotics and prednisone before leaving home just in case, so I began taking it. My recovery was slowly accomplished over the next few weeks and my wife had no symptoms, but few days before my first symptoms on 11/22, our onboard husband and wife friends from Prescott, Arizona, had gotten very sick with the same symptoms as mine.

    • Sir- 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

  • In the UK told different things what to do no one knows what to do no one’s being tested we just now to stay in 14 the hole family but the school still open and ever if thay are ill thay are still going around in thair lives nothing has changed I feel as thairs no laws put in place people are not doing as told I heard one lady in a shop I was in today say to the lady at the cheack out I’ve only popped out to get some shopping but I’ve got the family at home sick we need strick rulls and laws and shut everything down we have fears that soon people will be putting the Helth sistam under pressure and I can only see we be worse than Italy if the government don’t do more to slow this down as everyone won’t make the right choice to say in if thair sick we need a lock down and shut the pubs restaurant and school stop social mixing of people Ower government are putting us all at risk lock every one up till we get the vacsine it’s the only thing we all can do I do see people panic getting far too much tollet rolls and worry how thay pay the bills or how the government has not thort about the poor and how people will servive if thay can’t work the sick pay isn’t much at all and nit all will be able to even get that with zero hrs contract the government has not thort of homeless this is more than the cov19 we need now to help people through this we nerd to make shore thaurs food and as we are leaving the EU this is starting to feel life out of control if the government put on laws it will give us know what to do and kerp to the rulls I find it’s rilly confused in with what to do like even not to take Ibrahim thairs no parosole and other things

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