A Scottish research team has evaluated 79 studies on Sars-CoV-2 to find out when infected people are most contagious. On the basis of their results, they suggest a shorter isolation period - so that more people stick to the rules.
Stricter corona measures have been in place in Germany since December 1 - this also includes stricter contact restrictions to break chains of infection. Anyone who tested positive for Sars-CoV-2 must isolate themselves at home until the responsible health department cancels the measure. People who have had contact with the infected person from the second day before the onset of symptoms up to at least 10 days after the onset of symptoms must go into quarantine.
But when exactly does the sick person pose the greatest risk of infection? This is what a research team around the infectious agent and virologist Muge Cevik from the University of St. Andrew wanted to find out. Their results suggest that infected people may have to stay at home less than before - and the spread of the virus could still be prevented.
According to the Robert Koch Institute (RKI), the exact period in which the contagiousness exists has not yet been clearly defined; the information on this varied. It was considered certain, however, that the contagion is greatest around the onset of symptoms and that a significant proportion of the transmission occurs before the first clinical symptoms appear.
“In addition, it is certain that the contagiousness decreases in the course of the disease and that seriously ill patients sometimes excrete the infectious virus longer than patients with mild to moderate disease,” reports the RKI.
According to the current state of knowledge, in the case of mild to moderate illness, the contagion significantly decreases ten days after the onset of symptoms; In the case of severe illnesses, however, patients could be contagious for considerably longer than ten days after the onset of symptoms.
Researchers report a shorter risk of infection
In their systematic review and meta-analysis, the Scottish research team around Cevik have now come to different results, which they have published in the renowned specialist journal “The Lancet”.
Covid 19 patients had the highest viral load in the upper respiratory tract up to two days before their symptoms broke out and up to five days afterwards - then the risk of infection is greatest. Cevik emphasizes that it does not depend on the severity of the symptoms. “Anyone who notices signs of illness, no matter how mild, should isolate themselves immediately. Because by the time we get the test result, they could be past their most infectious phase. ”The earlier those affected isolated themselves, the better.
Asymptomatic infected people also seem to have about the same amount of virus in them as patients with symptoms. With them, however, the virus apparently disappears from the body more quickly, explains the researcher.
In addition to the studies on Sars-CoV-2, the scientists also evaluated eight studies on Sars-CoV-1 and eleven on Mers-CoV. Compared to Sars-CoV-2, the first Sars virus and Mers-CoV only multiply slowly in the upper airways - with Sars-CoV-1, virus excretion via the upper airways is highest after 12 to 14 days of infection, at Mers-CoV patients after 7 to 10 days. There is practically no transmission by asymptomatic or presymptomatic persons.
Cevik's team also came to the result that with a Sars-CoV-2 infection from day 9 onwards, there were no longer enough viable viruses detectable in the upper respiratory tract that could cause an infection: “In none of the studies was it higher despite persistently Viral load of a live virus detected after the 9th day of illness ”. However, the virus genes were still present for a long time in the upper and lower airways, in the blood and in the stool. But even here there is no risk of infection, stated Cevik.
However, this statement should be interpreted with caution, warned the "Ärzteblatt". Because the smears showed only individual virus genes with the polymerase chain reaction - they would not have to come from viruses capable of replication. It could therefore also be the remains of an infection that has already been overcome. Infectiousness cannot be completely ruled out.
According to the evaluated studies, the mean duration of a positive smear was 17.0 days in the upper airways, 14.6 days in the lower airways, 17.2 days in the stool samples and 16.6 days in the serum samples. The longest proven elimination times were 83 days in the upper airways, 59 days in the lower airways, 126 days in the stool and 60 days in the serum.
Based on their results, Cevik suggested reducing the isolation period to five days. This could, so her hope, bring more infected people to actually stick to the isolation, she told the "New York Times". Their reasoning is likely to be based on a survey from August that only 20 percent of respondents in Great Britain actually follow the rules of self-isolation.
Because of the "currently limited test capacities and the frequency of colds in the winter months", which makes it impossible to confirm all Covid-19 diseases in Germany through tests, the RKI also advises "if you have any respiratory symptoms for at least 5 Days to isolate at home and only end the isolation after another 48 hours without symptoms. "