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.
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.