How dangerous for me, sneezing people at the bus stop? Should I go to a restaurant? Or use public transport? As soon as the world is gradually emerging from quarantine and we return to the social environment and to our usual routine, increasing the risk of infection and spread of the coronavirus. It is the fear of a second wave of the epidemic, BBC reports.
The publication’s editors spoke with the immunologist and associate Professor University of Massachusetts in Dartmouth with a Erin Bromwich on how to reduce the risk of catching Covid-19.
Dr. Bromwich lectures on epidemiology of infectious diseases and closely monitoring the development of the current pandemic from the very beginning.
He is not so much the expert on this specific disease as a skilled popularizer of scientific knowledge. His blog about the risks associated with coronavirus, read about 16 million people.
Here’s what he advises to do in the period of at least a partial return to normal life.
Where you can pick up the infection?
Dr Bromwich said that most people infected in their own homes by another family member, which transmits the infection to all the others in the course of regular contacts.
And outside the home? If we put ourselves at risk during a daily walk in the Park? This frivolous runner without a mask — if he will give me now a disease?
Unlikely, says Professor.
“In the open air, the virus is sprayed in an unlimited amount, he explained in an interview with Bi-bi-si. The human exhale, dissipates very, very quickly.”
This means that your dose of virus is likely to be insufficient in order to get infected.
“So you got sick, your body needs to get the so-called infectious dose of the order of thousands of particles of the virus SARS-CoV-2. This estimate is based on research of appropriate doses with respect to MERS and SARS”, — he wrote in his blog.
Specific figure remains a subject of debate and needs to be confirmed experimentally, but it gives a useful overall picture of how a person becomes infected.
The point here is that you can dial the required dose in different ways.
“A thousand virus particles in one breath, or one hundred for ten breaths or ten for a hundred breaths. Any of these situations can lead to infection,” explains Dr. Bromwich.
This means that within a very short contact with an infected person — the same runner who does not understand the need to respect the distance you are unlikely to gain infectious dose.
In what situations should you worry more?
People with symptoms
Coughs and sneezes do spread infection, but in very different ways.
When you cough person at a time throws into the air about three thousand of tiny droplets at a speed of 80 km/h, said Dr. Bromwich. Most of them are large enough to fall to the ground under its own weight, but some can stay in the air and fly to the opposite end of the room.
If the person you ride the Elevator, don coughs and sneezes, the risk increases 10 times.
One sneeze is about 30 thousand particles moving at a speed of 320 kilometers per hour, and much smaller, so they can easily reach even to the far end of the room.
“If a person is infected, then he coughed or sneezed, every time allocates as much as 200 million virus particles,” — said Dr. Bromwich.
“If you are speaking to someone face to face, and that person coughs or sneezes directly on you, you, course, can easily get the infectious dose in a thousand viral particles,” explains the expert.
If you are not present when coughing and sneezing directly, you are still in danger. Some droplets can hover in the air for a few minutes and you entering the room, you have time to inhale enough of them.
We know that the first five days after infection, people get sick without symptoms, some do not appear at all, even later.
Viral particles enter the atmosphere and through regular breathing. But a lot of it?
“One exhale stands out from 50 to 5000 droplets. Most of them move slowly and almost immediately fall to the ground,” says Dr Coventry.
The number of drops is greatly reduced if the person is breathing by nose.
“The nose is an extension filter, and the air is directed vertically downwards. Thus, the number of allocated pathogens of viral particles is relatively small, experts say. — It is important that during normal breathing the air comes out without effort, so that viral particles from the lower respiratory tract it does not fall”.
This is important because in the lungs and trachea of an infected person, the concentration of coronavirus higher than in the throat and mouth.
How many particles of the virus SARS-CoV-2 (the current coronavirus, causing Covid-19) is released when breathing, is unknown. But Professor Bromwich cites studies according to which in the ordinary flu, the patient spreads from three to 20 viral particles per minute.
If these data are correct and for agent Covid-19, you, being in the presence of an infected person, has to get absolutely all of the allocated particles for 50 minutes to collect the infectious dose of a thousand particles (all figures are estimates and approximate).
To summarize, we can say that the probability of getting sick just by being in the same room as a carrier of infection is relatively small, if he sneezes and coughs.
However, most of the infections outside of the house probably comes as a result of contact with asymptomatic patients.
The risk increases about 10 times if you talk reminds Bromwich.
Dramatically increase the number emitted into the atmosphere in droplets of saliva singing and screaming.
“You should scream or start singing, and the droplets start to literally bombard the space in front of you, and they come from the depths of the lungs where the tissues of the infected stronger, says an expert. — In General, any force while inhaling sharply increases the contamination of the air.”
What places particularly dangerous?
Of course, those most at risk are those who because of their profession is dealing with infected people.
Also known cases of mass disease of people in certain places. In this respect, all in the memory of cruise ships. Dr. Bromwich refer to these environments and more open space, sporting and entertainment events, parties, funerals, choral rehearsals.
In all these cases, the risk of infection is great, since people spend considerable time indoors in the company of other people, among which there may be infection carriers.
“Even if a particular sick person is 15 meters away from you, as during choir practice or in the call center and the number of reaches you of the virus particles is small, for a long time you can dial the dose,” the scientist said.
As returns on jobs of particular concern are some professions.
Most problems are of open space with poor ventilation. Dr. Bromwich results in the case when South Korea’s 216 employees worked in one large open space, and 94 of them got sick.
Dentists in the General population are not many, but they are a particular risk.
“In the course of their work, drilling, extraction, and others, produce large quantities of aerosolized substances. The administration should consider how to organize the workspace in such a way as to protect its employees because the danger is primarily to dentists, not patients,” said Dr. Bromwich.
Another group of risk — teachers and teachers.
“Teachers and professors, mainly elderly people, should be a long time in the same room with the youth. It is necessary to thoroughly think over how to protect these jobs,” — says the expert.
On the air in the room
According to Bromwich, among the known episodes of mass infection, only very few have happened in the open air.
Wind and space dissipate the concentration of the virus, and the sun’s rays, heat and humidity can shorten the time of survival.
Supporting distance and reduce the duration of contacts, you reduce the risk even more.
But some closed spaces potentially very dangerous, especially events where people in crowded conditions talk to each other, singing and shouting, and where it is difficult to effectively maintain separation.
Problematic premises with bad ventilation, and air conditioning.
Here’s the shopping — at least for buyers — much less dangerous, at least if not to remain long in the same place.
Limitations associated with the coronavirus, are gradually removed, but we should critically evaluate the degree of danger of those or other classes, advises Dr. Bromwich.
If you are going to go in a closed space, take into account the cubic capacity, the number at the same time the people living there and the length of your stay.
“If you sit in a well ventilated area with a small number of people, the risk is small, the scientist said. — If you work in an open office, it is necessary to evaluate its volume, the number of people and ventilation. If your work requires contact face to face, especially loud talking and screaming, think again”.
For example, for a visitor of the shopping center, if he will stay there for long, visitors is not very much and the room volume is large, and the danger is not so great. For the warehouse worker, who spends the whole day there, it is much higher.
Outside the risk of infection is much smaller, since infected droplets dissipate quickly, but remember dose and time, says the Professor.
“So far, we talked about transmission of the virus by airborne droplets, but you can’t forget about the surfaces. Infected droplets are deposited anywhere. Wash your hands often and avoid touching the face,” said Bromwich.
And yet, perhaps, will have to abandon the custom to blow out the candles on your birthday cake.