Coronavirus: Two and a half days before symptoms start, people could be infectious

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Did she have symptoms or did she not have any? When the first corona cases in Germany were reported to a Munich auto supplier at the end of January, a discussion broke out about patient 0 – a Chinese businesswoman who was on-site for further training and had unwittingly passed on the corona virus. The first reports said that the woman had shown no symptoms during her stay. This was initially interpreted as evidence of asymptomatic transmission.

However, the denial followed later – from the patient herself. She had already felt uncomfortable in Germany and had taken antipyretic drugs, and not, as had previously been reported, only on her return flight to China. The question remained: is the pathogen infectious before the onset of the symptoms of the disease?

At that time, there were already initial reports of illnesses in China, which apparently had infected people with no recognizable symptoms. However, international experts were initially skeptical. They suspected that these people might have had contact with a symptomatic patient – without knowing about it.

A study from Hong Kong now provides further information for asymptomatic transmission of Sars-CoV-2. The investigation comes from a team of researchers led by clinician Gabriel Leung. It has not yet appeared in any scientific specialist magazine, so it has not yet been extensively reviewed. As the Berlin-based virologist Christian Drosten revealed in yesterday’s episode of his NDR podcast, he believes the study is of high quality. Drosten himself had already analyzed data from the Munich patients: “This study has shown that the throat virus replicates in the early phase of the infection and that the virus can be detected even in the earliest smears, so that it can be seen on day one and two is on the descending branch. “

Transmission possible before the onset of symptoms

Chinese researchers have now come to similar results, evaluating data from 94 patients from Guangdong in southern China. “That means the peak of the virus must be before day one,” said Drosten. It differs significantly from the well-known Sars-1 pathogen: “This was so good to contain because it only really becomes infectious in the average patient long after the onset of symptoms.”

The scientists around Leung also examined data from 77 couples, one of which infected the other. The researchers wanted to know: how long is the time from the onset of symptoms in one partner to the onset in the other? This interval is called “Serial Interval” – Drosten says. In the study, this ranged between 5.2 and 5.8 days on average. This means that the series interval is roughly in the range of the mean incubation period, which is also given as 5.2 days. “This tells us that the middle patient actually waits for the symptoms after infection as long as it takes to transmit this infection between two patients,” said the expert.

“This means that not only do we start transmitting on average on the day of symptom onset, but probably before that as well. The middle patient is practically transmitted on the day of symptom onset, but that’s only the middle patient. Some patients are only transmitted after symptom onset and unfortunately some are transmitted even before the onset of symptoms. That is a probability distribution that can be calculated. ” One can assume that 44 percent of all infection events took place before the person infected was even ill, according to Drosten. He assumes that the infectivity starts on average two and a half days before the onset of symptoms.

The result would clarify how important distance regulations are. Those who lock themselves in at home only when the first signs of illness appear have already infected people with normal social interaction. This disease cannot be contained with the usual rules of infection protection – symptom detection and isolation – says the virologist. Instead, people would have to distance themselves from each other – “in a targeted way”.

Source: NDR info


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