Coronavirus transmission: Study on a Munich case group provides comprehensive insights

Coronavirus transmission: Study on a Munich case group provides comprehensive insights

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First study in German COVID-19 sufferers published

The first major study in German COVID-19 sufferers recently appeared. Research director Professor Christian Drosten and his team examined a Munich case group in detail. In this way, comprehensive knowledge about the transferability of the coronavirus SARS-CoV-2 was obtained, from which new recommendations for treatment can be derived.

Researchers from the Charité - Universitätsmedizin Berlin, the Munich Klinik Schwabing and the Institute for Microbiology of the Bundeswehr were able to document detailed observations of the course of infection of COVID-19 in affected people from Germany. The results were recently presented in the renowned journal "Nature".

Munich case group examined in detail

The first coherent COVID-19 cases in Germany were recognized in the district of Starnberg near Munich at the end of January. Nine of these cases were treated in the Munich Clinic Schwabing and simultaneously examined in detail. "At that point, we really knew very little about the novel corona virus that we now know as SARS-CoV-2," explains Professor Dr. Christian Drosten, Director of the Institute of Virology, who, together with Professor Dr. Clemens Wendtner, chief physician of infectious diseases and tropical medicine at Munich Clinic Schwabing, who led the study.

Who are the patients examined?

"We have therefore examined these nine cases very closely virologically across their course of the disease - and learned so many important details about the new virus," adds Professor Wendtner. The patients looked after were younger to middle-aged and showed rather mild, flu-like symptoms such as cough and fever as well as a disturbed taste and smell.

"For the scientific significance of our study, it was advantageous that the cases were all related to an index patient and were not only examined for certain symptoms," emphasizes chief physician Wendtner. In this way, the virological process could be well documented in order to derive important insights into transferability.

The course of the investigation

For the patients, smears from the nasopharynx as well as samples of the cough sputum were taken and analyzed daily over the entire course of the infection. These studies continued up to 28 days after the onset of symptoms. In addition, stool, blood and urine samples from the participants were collected and evaluated at several times during the illness. All samples were then analyzed in two independent laboratories - one from the Bundeswehr Institute for Microbiology and the other from the German Center for Infection Research (DZIF).

What are the key findings of the study?

The researchers found that the virus excretion in the throat of those infected with COVID-19 was very high, especially in the first week after the onset of symptoms. This was also evident in the cough sputum. Infectious virus particles could be isolated from both samples. "This means that the new corona virus can multiply not just in the lungs, but already in the throat and is therefore very easy to transmit," emphasizes Professor Drosten.

The viral load decreased significantly in most of the participants examined during the first week of illness. The viral load in the lungs also decreased, but later than in the throat. Eight days after the onset of symptoms, the researchers were unable to isolate infectious virus particles. From this point on, COVID-19 no longer appears to be infectious (or significantly less).

SARS-CoV-2 is highly contagious in the early stages of the disease

"The high viral load in the throat right at the beginning of the symptoms indicates that COVID-19 sufferers are infectious at a very early stage, possibly even before they even notice that they are sick," summarizes Dr. Roman Wölfel, Director of the Bundeswehr Institute for Microbiology.

In addition, there seems to be a connection between the viral load in the throat and lungs and the infectiousness. According to the research team, this is an important factor in deciding when infected people can be released from the hospital at the earliest if their bed capacity is limited. The research team concludes that COVID-19 patients can be released into home quarantine if less than 100,000 copies of the virus genome are detected in the cough sputum after the tenth day of the disease.

When do antibodies form?

The study also provides information about when antibodies are formed. The blood serum samples showed that half of the patients examined had developed antibodies against the virus on the seventh day after the onset of the disease. After two weeks, all participants had produced antibodies. "The onset of antibody production was accompanied by a slow decrease in the viral load," the researchers write.

Is urine and stool infectious?

Although the researchers found evidence that the SARS-CoV-2 coronavirus also spreads in the gastrointestinal tract, no infectious viruses could be detected in the stool and urine samples.

Differences to SARS

Even though SARS-CoV-2 has a genetic similarity to the old SARS virus, the research team was able to find clear differences. The old SARS virus only affects the lungs and is therefore significantly less infectious. "Instead, our investigations by the Munich case group showed that the new SARS coronavirus differs greatly from the old one in terms of the affected tissue", sums up virologist Drosten. Of course, this has enormous consequences for the spread of the infection.

What's next?

The research team is now devoted to immunity to SARS-CoV-2. In another study on German patients, the aim is to find out exactly how long-term immunity to SARS-CoV-2 develops. Among other things, these analyzes are of great importance for the development of vaccines. (vb)

Author and source information

This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.

Graduate editor (FH) Volker Blasek


  • Charité Berlin: Coronavirus: Virological details of the Munich case group (published: April 1, 2020),
  • Christian Drosten, Clemens Wendtner, Roman Wölfel, u.a .: Virological assessment of hospitalized patients with COVID-2019; in: Nature, 2020,

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