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May 13, 2020
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Risks: how to recognize and avoid them

The President of the Russian Federation invited the regions to develop measures for a gradual exit from the regime of self-isolation. Not so long ago, quarantine restrictions began to be lifted in various US states. Similar situations raise similar questions and concerns. Will there still be a risk of infection after lifting the restrictions? How safe is it now to go to the office, to the store, visit a restaurant, use public transport, talk with someone on the street? We present to your attention a translation of an article by an American biologist Erin Bromage (Erin Bromage), in which he examines these problems in detail, with examples, and answers these questions.

Many people seem to sigh with relief, but I don’t know why. The epidemic curve has a relatively predictable rise, and as soon as it reaches a peak, the descent can also be predicted. We have reliable data on outbreaks in China and Italy, which show how the number of deaths is slowly decreasing, but mortality persists for several months. If the peak fell on 50 of thousands of deaths, it is possible that over the next six weeks, until the curve decreases, we will lose more 50) person. And this is subject to quarantine.

As the states open, the virus will receive more fuel, which means that forecasts will lose relevance. I understand why there is a desire to restart the economy, but, as I said earlier, if the biology issue is not resolved, the economy will not recover.

Only a few states show a steady decline in the number of new infections. Indeed, as of May 3, the majority of patients is growing, but they remove quarantine. Let me give you a simple example of a trend in the United States: if you exclude data for New York and look at the rest of the United States, it turns out that the number of new cases per day increases. Bottom line: the only reason the graph of the total number of new cases in the United States now seems to be even is that the epidemic in New York was very large, but now it is under control.

( as of May 3)

Thus, in most of the US, we will add oil to the viral fire, removing the restrictions. This will happen independently of me, so the goal of my post is to help you avoid excessive risks.

Where do people get sick?

We know that most people become infected at home. Household members become infected with the virus in society and bring it home, where constant contact between household members leads to infection.

But how do people get infected in society? I regularly hear people worried about grocery stores, bike rides, irresponsible runners without masks ... Is that cause for concern? Not really. Let me explain.

In order to get infected, you need to get an infectious dose of the virus. Based on studies of infectious doses with MERS and SARS, some believe that infection requires everything 900 SARS-CoV-2 virus particles. Note that this still needs to be determined experimentally, but you can use this number to demonstrate how infection can occur. You can become infected by inhaling once 760 viral particles or just rubbing your eyes or inhaling times by 92 virus particles, or 90 inhaling once . Each of these situations can lead to infection.

How much virus enters the environment?

Restrooms: in the latrines there are quite a lot of surfaces that people often touch - door handles, faucets, entrance doors. Thus, the risk of transmission of the virus through surfaces in this environment can be high. It is still unknown whether fecal virus is released or only its “debris”, but it is known that flushing the toilet leads to aerosolization of many drops. Be especially careful in public toilets (both with surfaces and with air) until more data appears.

Cough: when a person coughs once, he gives out about 1140 drops, and the drops spread with speed 31 miles per hour (70, 5 km / h). Most drops are large and quickly settle (due to gravity), but many remain in the air and can cross the room in a couple of seconds.

Sneezing: when a person sneezes once, it highlights about 20 drops, while the drops move at a speed of up to 99 miles per hour (200 km / h). Most drops are small and spread over long distances (across the room - with ease).

If a person is infected, drops from one cough or sneezes may hold up to 100) (two hundred million) virus particles that may be in their environment.

Breath : one exhale releases 31 - 2020 ka) spruce. Most of these drops are slow and quickly settle to the ground. When breathing through the nose, drops are released even less. It is important to note that due to the lack of exhalation force when breathing, viral particles are not removed from the lower respiratory tract.

Unlike sneezing and cough, which secrete a huge amount of viral material, drops released during breathing, contain quite a bit of virus. The specific numbers for SARS-CoV-2 are not yet known, but we can be guided by knowledge of the flu. We know that a person infected with the flu gives off about 3 - 10 copies of viral RNA

per minute of breathing.

Remember the formula:

infection = virus exposure × time

If a person coughs or sneezes, 100) virus particles spread everywhere. Some viruses freeze in the air, some settle to the surface, most fall to the ground. So if you are talking with a person face to face and that person is sneezing or coughing right at you, it’s pretty obvious that you can breathe in 1000 virus particles and become infected.

But even if a person coughs or sneezes to the side, some infected droplets - the very smallest - can freeze in the air for several minutes, filling the entire space of a small room with infectious virus particles. That is, it will be enough to enter this room a few minutes after something has coughed / sneezed and take several breaths in order to most likely receive a sufficient dose of the virus for infection.

During normal breathing with an ejection 10 copies in minute into the environment, and when every particle of the virus enters the lungs, it will take 900 copies divided into 10 copies per minute = 44 minutes.

Conversation increases the drop emission by approximately times: ~ 100 copies of the virus per minute. Assuming that all particles of the virus are inhaled, it will take ~ 5 minutes of face-to-face conversation to get the required dose.

Formula " exposure to virus × time ”is the basis for contact tracking. Anyone with whom you spend more minutes face to face, potentially infected. Anyone with whom you spent a long time in the same room (say, in the office).

This is why it is especially important that people with symptoms stay at home. Sneezing and coughing produce so many viruses that they can easily infect an entire room of people.

What is the role of asymptomatic carriers in the spread of the virus?

People with symptoms are not the only way to spread the virus. It is already known that at least 28% of all infections - and most transmitted internally - come from people without any symptoms (asymptomatic or presymptomatic people). People can release the virus into the environment 5 days before the onset of symptoms.

Infectious people are found in all age groups, and all of them different amounts of virus are secreted. The figure below shows that regardless of age (X axis), a person can secrete a few or many viral particles (Y axis). (source)

The amount of virus secreted by an infected person varies during the course of the illness and differs from person to person. Viral load usually builds up until the person has symptoms. Thus, shortly before the onset of symptoms, the patient releases the most virus into the environment. Interestingly, the data shows that only 10% of infected people are responsible for 90% viral load that could potentially be released into the environment (source)

So, it's time to get to the point. What are the personal risks when quarantine is weakened?

What major outbreaks of disease come to mind in the first place? Most will remember cruise ships. But this is not true. Today, ships do not even make it to the top - 31.

If you do not consider the terrifying outbreaks in nursing homes, it turns out that most infections occur in prisons, places of worship, and workplaces such as meat processing plants and call centers. Any environment with poor air circulation and high density of people can cause problems.

Here are some examples of the super-spread of the virus:

  • Meat industry: meat processing plants have a high density of employees, and they must interact with each other in the deafening noise of industrial equipment and in refrigerated rooms that well preserve the virus. The flashes are currently fixed at 99 factories in 16) states, more 2007 workers are infected and 05 died (link).

    Weddings, funerals, days birth: % of infections at the beginning of the epidemic.

  • Conferences: personal business communication, for example, the Biogen conference in Boston in March.

    11 этаж

    Let's see what happens when we get back to work or go to a restaurant.

    Restaurants: A few examples of field epidemiology have clearly demonstrated how one asymptomatic vehicle in a restaurant affects others (see below). The infected person (A1) dined at the same table with nine friends. Dinner lasted from one to one and a half hours. During dinner, an asymptomatic vehicle simply breathing low levels of the virus into the air. Airflow (from the air vents in the restaurant) moved from right to left. Order 31% of people at the infected table got sick over the next seven days. 67% of people from the next table, sitting by the movement of air, became infected. And even two out of seven people from the table on the other side of the air flow were infected (presumably due to the turbulent air flow). No one at the E or F tables got infected, they were outside the main air flow going from the air conditioner on the right to the exhaust fan on the left (source).

    Offices: Another eloquent example is a flash in a call center (see below). One infected worker came to work at - floor of the building. On this floor was 115 employees. During the week 94 of them became infected (28, 5%: blue chairs) . 80 of these 92 people became ill (only two did not show symptoms). Please note that first of all, one side of the office was infected, and few people became infected on the other side. It is not known exactly how people were infected: by respiratory drops / inhaling viral particles or transmission through surfaces (door handles, water coolers, elevator buttons, etc.). But I want to emphasize that being in a confined space with the same air for a long period increases the likelihood of infection. Three more people on other floors of the building were infected, but the authors could not associate the infection with the primary cluster on 000 - m floor. It is particularly interesting that despite the significant interaction between workers from different floors in the elevators and in the lobby, the outbreak was mainly limited to one floor (source). This emphasizes the importance of exposure and time during the distribution of SARS-CoV-2.

    Choir: is a church choir in Washington state. People knew about the virus and took steps to minimize transmission: for example, they avoided the usual handshakes and hugs, brought their notes to not use together, and socially distanced themselves during practice. One asymptomatic carrier has infected most of those present. The choir sang for two and a half hours in a closed church about the size of a volleyball court.

    Singing , more than speaking, sprays respiratory drops. Deep breathing while singing facilitates the penetration of respiratory drops into the lungs. Two and a half hours was enough for people to be exposed to the virus in the quantities necessary for infection. For four days at from 44 members of the choir developed symptoms of the disease, two died. The youngest infected was 24, the average age was 45 years (link).

    Indoor Sports: perhaps this is a unique Canadian case - Superspread occurred during curling competitions in Canada. The event was attended by 67 person, and it has become a "hot spot" of transmission of infection. During the curling game, competing teams are in close contact with each other in a cool, enclosed environment for a long time and can breathe heavily. As a result of this tournament 19 of 60 a person became infected (link).

    Birthdays / funerals: to illustrate how simple they can be be infectious chains, tell the real story that happened in Chicago; the name is replaced by a fictitious one. Bob was infected, but did not know about it. Bob shared a takeaway meal served in a shared bowl with two family members. Dinner lasted three hours. The next day, Bob attended the funeral, where, expressing condolences, he hugged family members and other people present. Within four days, both members the families with whom he had dinner get sick. The third member of the family who embraced Bob at the funeral was also ill. But Bob did not stop. He attended a birthday party with nine other guests. They hugged and ate together at the party for three hours. Seven of them got sick. A few days later, Bob fell ill, was hospitalized, got on mechanical ventilation and died.

    But Bob’s legacy continued to live. Three of the people infected by Bob at the birthday party went to church, where they sang, passed the alms bowl, etc. The members of this church are sick. In general, Bob infected directly 000 people aged 5 to 72 years old. Three of these died.

    The transmission of the virus inside the household and back to society - at funerals, birthdays and church meetings - is responsible for the widespread spread of COVID, it is believed - 05 in Chicago (link).

    Sobering up, isn't it?

    What do the flashes have in common

    I highlighted these flashes to show what the different COVID flashes have in common - 05. All these infections occurred in rooms where people were close to each other, talked a lot, sang or shouted. The main sources of infection are home, office, public transportation, events, and restaurants. This makes up the order 75% of all infections. Stores, on the contrary, are responsible for a small percentage of infections that have been tracked (source).

    It is important to note that in countries in which are properly tracked by contacts, there was only one outbreak in the open air (less than 0.3% of detected infections) (source).

    So, back to the original thought of my post

    The premises for a large number of people with limited air exchange or air recirculation are of most concern in terms of virus transmission. We know that the simultaneous presence 43 a person (choir) in a hall the size of a volleyball court caused a massive outbreak of infection. The same thing happened in the restaurant and call center. Recommendations on social distance do not help in rooms where people spend a lot of time: people on the opposite side of the room are infected.

    Principle - exposure to the virus for a long period of time. In all these cases, people were exposed to the virus in the air for a long time (several hours). Even if they were at a distance 31 ft) (chorus or call center), even if the number of viral particles in the air was small, the virus for a long time, it was enough to cause infection, and in some cases death.

    Social distance is enough to protect during brief exposure or exposure on the street. In these situations, the time to achieve an infectious viral load is not enough if you stand 6 feet apart or where the wind and open air dilute the concentration of particles and reduce the viral load. Sunlight, heat and humidity affect the survival of viruses - all this reduces the risk in the open air.

    Assessing the risk of infection (through breathing) in a grocery store or shopping center, it is necessary to take into account the amount of air space (very large), the number of people (limited), the time that people spend in the store (employees - all day, customers - an hour). In total, for the buyer: low density, a large amount of air in the store and the limited time he spends there mean that the probability of getting an infectious dose of the virus is small. But store employees spend more time there, which makes it more likely to receive an infectious dose, and, therefore, for them, work becomes more risky.

    In fact, as the restrictions relax, we will begin to go out more often, perhaps even resume work in the office, and you will need to monitor the environment. How many people are here, how much air and how much time I am going to spend here. If you work in an open-plan office, you need to critically assess the risks (volume of the room, number of people and air flow). If you need to talk at work, or, even worse, scream, you need to assess the risk.

    If you are sitting in a well-ventilated in a place where there are few people, the risk is low.

    If I’m on the street and walking past someone, remember that for infection "dose and time" are needed. You must be in someone else's air stream for at least five minutes for the risk of infection. Although runners can secrete more virus because they breathe deeper, remember that exposure times are reduced due to their speed.

    Although the post is about respiratory effects, please do not forget about the surfaces. The infected droplets land somewhere. Wash your hands often and don’t touch your face!

    As we are allowed to move more freely and have regular contact with a large number of people in more places, the risks for us and family members are increasing. Even if you are anxious to return to normal life, do your part and put on a mask to reduce the release of the virus into the environment. This will help everyone, including your business.

    This post was inspired by an article written by Jonathan Kay in Quillete

    : COVID - 05 Superspreader Events in 20 Countries: Critical Patterns and Lessons.

    About the author

    Erin S. Bromage, PhD , associate professor of biology at the University of Massachusetts Dartmouth. Dr. Bromage graduated from the School of Veterinary and Biomedical Sciences of the University. James Cook, Australia, where his research focused on epidemiology and immunity to infectious diseases in animals. His postdoctoral training was held at the College of William and Mary, Virginia Institute of Marine Science, at the Laboratory of Comparative Immunology of the late Dr. Stephen Kaattari.

    Dr. Bromage's research focuses on the development of the immune system, the immunological mechanisms responsible for protecting against infectious diseases, and the development and use of vaccines to fight infectious diseases in animals. He also develops diagnostic tools for real-time detection of biological and chemical threats in the environment.

    Dr. Bromage began working at the Department of Massachusetts University in Dartmouth at 2007 year, he gives courses in immunology and infectious diseases, including this semester a course in the ecology of infectious diseases dedicated to SARS-CoV-2's new outbreak China.

    Translation was made specifically for the channel "Rat ionically about coronavirus ”.

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