Medical staff check a patient while he sits in his car at a drive-in testing site for coronavirus (COVID-19) at the Regional Hospital Center in Liege, Belgium March 11, 2020. REUTERS/Francois Lenoir
Berlin: 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 outsides 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.
"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 Minnesotas Center for Infectious Diseases Research and Policy.
The researchers monitored the viral shedding of 9 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 were 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 a little residual risk of infectivity, based on cell culture."
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 the virus occurred later, when the virus had moved into the deep lungs.
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.
