Where the risk of infection is high

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Where the risk of infection is high





© AFP
A man with a protective mask disinfects the handrails of an escalator in Tokyo.


Doorknob, packages, pets? Researchers are finding out more and more about the transmission pathways of the corona virus. How Sars-CoV-2 spreads and how people can best protect themselves.

Where the risk of infection is high

There was never so much distance. Most people have long since internalized that they should avoid contacts and keep at least 1.5 meters away from their fellow human beings. Even children know that the hands belong on the face and should be washed with soap as often and as long as possible. Cough and sneeze occurs in a handkerchief or the crook of the arm. Only: is that enough? How safe is it to protect yourself against Covid-19 lung disease if you strictly follow all the rules? What scientists have found so far about the transmission of the Sars-CoV-2 pathogen.

How is the pathogen transmitted?

Infected send the pathogens with droplets, which arise when sneezing, coughing, maybe even when speaking. Once on the go, Sars-CoV-2 has only one goal: to get into another person’s airways to hijack new cells where it can multiply. If the pathogen is lucky, the direct route is open to him. It then gets into the mouth, nose or eyes of another with the gush of droplets. The virus is occasionally forced to take detours. It then lands on the face or hands of the coughed person, who often transports it unnoticed while scratching his nose or licking his finger. The pathogen can also first wander from hand to hand or possibly take a detour via a door handle or other surface. The longer and more complicated the route of the viruses, the less likely they are to reach their destination in sufficient quantities. The Robert Koch Institute (RKI) assumes that the pathogens are mainly transmitted directly.

When is an infected person contagious?

The timing varies greatly. On average, however, infected people experience the first symptoms about six days after the infection. However, two days before cough, fever, body aches or other symptoms appear, infected people can infect others. This means that people who do not yet know anything about their disease can also transmit the pathogen. This phenomenon makes the fight against Covid-19 extremely difficult. How long people remain infectious is not yet certain. The rule therefore applies that sick people should remain isolated for at least 14 days. In addition, they should have been free of symptoms for at least two days before being allowed to leave the house. It is also not yet certain whether infected people who do not develop any symptoms can pass on the virus.

What is the probability of getting infected?

Statistically speaking, anyone who only meets a few people initially has a low risk of encountering an infected person at all. Even if you assume 100,000 people are currently infectious in Germany and assume that the individual gets close enough to about ten people during the day, the likelihood that there is an infectious person among them is mathematically 1.2 percent. And even if this person meets an infectious contemporary, he does not necessarily have to be infected.

Researchers analyzed nine social situations in which infected people met healthy people; in most cases, they had a meal together. On average, only 35 percent of those present were infected. Those who are infected do not necessarily have to get sick. According to various analyzes, between 70 and 85 percent of all infected people get sick. Under certain circumstances, however, all of these risks can be much greater. If the pathogen reaches an old people’s home or an overcrowded refugee shelter, for example, many more people can be infected and then possibly suffer badly.

How long does the pathogen stay on surfaces?

Two studies suggest that Sars-CoV-2 can persist on plastic and stainless steel for up to four days. Viruses could still be detected on a banknote after two days, on textiles and cardboard after one day. On the other hand, no pathogens were detectable on paper after three hours. The amount of viruses decreased very quickly on all tested surfaces. It is not certain how great the risk is that the pathogens will still infect an object after a long period of time. If you are concerned about the contamination of objects in public space, you should also ask yourself how likely it is that a pathogen has come onto a surface at all. The pack of salt from the bottom shelf in the supermarket should be less risky than the handle of the shopping cart, which many other people have previously touched. Even the package that the postman carefully hands in does not pose a major risk of infection. Customers can protect themselves by washing their hands, and possibly also by disinfectants. So far, there is no indication that the coronavirus is transmitted via food.

What temperatures make Sars-CoV-2 harmless?

If you set the 60-degree program on the washing machine or dishwasher, you should reliably deactivate the viruses. In experiments, the virus was no longer detectable after five minutes at an ambient temperature of 70 degrees. At 56 degrees Celsius, it was inactivated after 30 minutes at the latest. The pathogen tolerated temperatures between four and 37 degrees better – and was detected between one and 14 days. But there is help even at low temperatures: The viruses can be rendered harmless by fat-soluble substances such as surfactants. Such substances are contained in common detergents and dishwashing detergents as well as in soap. They destroy the layer of fat that surrounds the Sars-CoV-2 genome.

Can you get infected with your pet?

At first it was only a spitz in Hong Kong, in whose snout the corona virus was found. Then at least one other dog and two cats tested positive for the corona virus. In experiments, too, cats became infected and then passed the virus on to other members of the species. So far, however, there is no evidence that the animals excrete quantities of virus that are sufficient to infect humans. The Friedrich Loeffler Institute responsible for animal health therefore sees no reason for people to restrict their contact with pets or to give up their pets. As always, however, the hygiene advice applies: keepers should keep animals away from their faces and wash their hands thoroughly after contact. If you yourself are ill, you should protect the animal with sufficient distance. The first cautious all-clear has already been given to farmers. At least pigs and poultry do not appear to be susceptible to Sars-CoV-2 infection.

Is there any danger from drinking water or wastewater?

So far, there is no evidence that the new corona virus can be transmitted through drinking water. Both the World Health Organization (WHO) and the Federal Environment Agency (UBA) argue that the envelope of the virus is comparatively sensitive to environmental influences or chemicals such as chlorine. The UBA also points out that drinking water in Germany is protected from pathogens by several different barriers. Among other things, filters and disinfection measures eliminate viruses from tap water. “According to the current state of knowledge, a transmission of the corona virus via the public drinking water supply is highly unlikely,” writes the authority. The extent to which the Covid 19 pathogen is widespread in wastewater has not yet been clarified. It is known that up to ten percent of sufferers suffer from diarrhea. In individual cases, the pathogen has already been found in the stool of patients. However, there is currently no indication that this route plays a role in the transmission of the infectious disease.

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