12-Nov-2020 - Max-Planck-Institut für Chemie

COVID-19: Calculating aerosol infection risk yourself

Algorithm to estimate coronavirus infection risk from aerosol transmission in the indoor environment and under different safety measures

An easy-to-use algorithm can now be used to determine the risk of being infected by SARS-CoV-2 via aerosol particles from patients in indoor environments. It also estimates how protective measures such as wearing masks and ventilation reduce the risk. The model, developed by researchers at the Max Planck Institute in Chemistry in Mainz, uses parameters such as the size of the room, the number of people in it and their activity to estimate both the individual risk of COVID-19 infection and the risk of anyone in the room. The algorithm is publicly available via an input mask on the institute's website. It calculates infection risk by micrometer size aerosol particles, but not by larger droplets in cas of close contact with an infected person. The approach complements standard protection measures.

Even though experts have not yet reached full agreement, many assume that aerosol particles play an important role in the transmission of SARS-CoV-2 viruses. The aerosols are created when breathing, talking and singing. Unlike droplets, they don't fall to the ground quickly, but can stay in the air for a long time and spread throughout the room. Indoor situations where many people are together for an extended period are particularly critical for infection with COVID-19. But how high is the risk of infection really? And how much can it be reduced by wearing face masks and active ventilation?

Researchers at the Max Planck Institute for Chemistry (MPIC) and the Cyprus Institute (Cyprus) have now published a study in which they present an easy-to-use spreadsheet algorithm to estimate the probability of COVID-19 infections through indoor aerosol transmission. The algorithm is publicly available, and can also be operated from website of the Max Planck Institute for Chemistry. You can enter various parameters such as room size, number of people and duration of stay at a particular location.

Various scenarios: classroom, office, reception, choir rehearsal

The algorithm automatically calculates the probability of transmission if one person in the room is highly infectious both the individual risk of infection and that for any other person in the room. You can select different scenarios: a classroom, an office, a reception (or party) and a choir rehearsal. Experts can also use available fields for information such as the infective dose, the virus load of the infected person and the survival time of the virus in the air. The filter efficiency of face masks or the air exchange rate can also be flexibly entered.

“We want to make a contribution so that the likes of a school or an office can independently calculate how high the risk of infection is on their premises, and how effective each possible safety measure is,” says Jos Lelieveld, Director at the Max Planck Institute for Chemistry and first author of the study published in the International Journal of Environmental Research and Public Health.

In their study, the scientists present the concept and assumptions on which the calculations are based. On average an adult inhales and exhales around 10 litres of air per minute. The researchers assume that the average dose for someone to become infected with Covid-19 is around 300 viruses or RNA copies per person. The calculation is illustrated by a school class in which no safety measures are taken: a 60 m2 classroom measuring 3 m from floor to ceiling, with 25 students aged ten and above attending six hours of lessons, where one of the students is highly infectious for two days.

According to the calculation, the probability that a particular person will become infected under these circumstances is just under 10%, but the probability that any person will become infected is over 90%. Infection is therefore almost inevitable. An individual with Covid-19 is usually highly infectious for a few days. In relation to all people who test positive for Covid-19, an average of around 20 percent is typically highly infectious. They are not to be confused with the so-called superspreaders, of which it is not well known how often they occur.

Variables allow individual use of the model

“Our calculations show that the risk of infection can be reduced by up to a factor of two by regular, active ventilation, and by a factor of five to ten by additionally wearing face masks,” adds atmospheric researcher Lelieveld. Taking the school class as an example, this means that if the windows are opened every hour, the probability can be reduced from 90 to 60 percent. In addition, if all students wear masks, the risk of infection drops to around 24 percent. If you enter in the website calculator that only half of the number of students are taking part in the lessons, the probability of transmission drops to 12 percent. At the same time, the individual risk drops from ten percent to one percent.

The model only determines the risk of infection via the aerosol particles, which are so small that they remain in the air for a long time and are distributed throughout the room. It does not allow any statements about the risk of becoming infected via larger droplets that fall quickly to the ground over short distances, for example from coughing or sneezing.

In their publication, the researchers also address the uncertainties in the calculations. These are, for example, related to assumptions such as the survival time of the Sars-CoV-2 viruses in the air and the number of viruses that an infected person gives off. Another point of uncertainty is how many virus particles actually cause a Covid-19 infection, as this can vary between susceptible persons and cannot be directly measured. "Our assumptions are based on the current state of the science," says Frank Helleis, physicist at the Max Planck Institute for Chemistry. “There are variables in the calculation. Hence it makes a difference if and how many people in a room will speak and sing or what exchange rate with outside air is applied, "says Helleis, who designed the algorithm.

Helleis and colleagues are convinced that their algorithm can help many people to assess the risk of infection in indoor environments and to reduce it by taking the appropriate measures.

Facts, background information, dossiers
  • SARS-CoV-2
  • aerosol particles
  • Covid-19
More about MPI für Chemie
  • News

    Humans transport dangerous smoke residues indoors

    Decades of research have demonstrated the adverse effects of fine particulate matter and volatile organic compounds (VOC) such as nicotine or acetonitrile from tobacco smoke on human health, with no “safe” level of exposure. Smoking restrictions have decreased non-smokers’ exposure to secon ... more

    Air pollution is one of the world's most dangerous health risks

    Polluted air is a public health hazard that cannot be evaded. It is widely known that long-term exposure to air pollution enhances the risks of cardiovascular and respiratory diseases. Scientists from the Max Planck Institute for Chemistry and the University Medical Center Mainz now calcula ... more

    New momentum for Open Access

    A new approach should give a fresh boost to Open Access, the unrestricted online access to scholarly research articles. This is the result of an international conference in Berlin, where a process was initiated to transform subscription journals to Open Access. The key to this lies in the h ... more

More about Max-Planck-Gesellschaft
  • News

    We Wouldn’t Be Able to Control Superintelligent Machines

    We are fascinated by machines that can control cars, compose symphonies, or defeat people at chess, Go, or Jeopardy! While more progress is being made all the time in Artificial Intelligence (AI), some scientists and philosophers warn of the dangers of an uncontrollable superintelligent AI. ... more

    Keeping Sperm Cells on Track

    One essential component of each eukaryotic cell is the cytoskeleton. Microtubules, tiny tubes consisting of a protein called tubulin, are part of this skeleton of cells. Cilia and flagella, which are antenna-like structures that protrude from most of the cells in our body, contain many micr ... more

    A clear path to better insights into biomolecules

    An international team of scientists, led by Kartik Ayyer from the MPSD, has obtained some of the sharpest possible 3D images of gold nanoparticles. The resuts lay the foundation for obtaining high resolution images of macromolecules. The study was carried out at the European XFEL’s Single P ... more

  • Videos

    Epigenetics - packaging artists in the cell

    Methyl attachments to histone proteins determine the degree of packing of the DNA molecule. They thereby determine whether a gene can be read or not. In this way, environment can influence the traits of an organism over generations. more

    Biomaterials - patent solutions from nature

    Animals and plants can produce amazing materials such as spider webs, wood or bone using only a few raw materials available. How do they achieve this? And what can engineers learn from them? more

    Chaperones - folding helpers in the cell

    Nothing works without the correct form: For most proteins, there are millions of ways in which these molecules, composed of long chains of amino acids, can be folded - but only one way is the right one. Researchers in the department "Cellular Biochemistry" at the Max Planck Institute for Bi ... more

  • Research Institutes

    Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V.

    The research institutes of the Max Planck Society perform basic research in the interest of the general public in the natural sciences, life sciences, social sciences, and the humanities. In particular, the Max Planck Society takes up new and innovative research areas that German universiti ... more