# Airborne disease transmission in a well-mixed room: Airborne transmission rate | Summary and Q&A

1.4K views
April 8, 2021
by
MIT OpenCourseWare
Airborne disease transmission in a well-mixed room: Airborne transmission rate

## TL;DR

Transmission rates and infection quanta determine the rate at which individuals become infected in indoor spaces.

## Questions & Answers

### Q: How is transmission between an infected person and a susceptible person explained?

Transmission occurs when the susceptible person breathes in infected droplets, and the infectivity of a virion, along with the mask factor, determines the probability of infection.

### Q: What determines the number of new infections per time?

The number of new infections per time depends on the transmission rate, beta, which is the rate at which a susceptible person becomes infected, and factors such as the concentration of virions per volume and the flow rate at which the susceptible person samples the air.

### Q: What is the role of infectivity and the mask factor in transmission?

Infectivity refers to the probability that an individual virion causes a person to become infected. The mask factor represents the transmission or penetration probability of droplets through a mask and plays a role in reducing transmission rates.

### Q: How can the steady-state transmission rate be calculated?

The steady-state transmission rate, termed beta bar, is determined by the steady-state concentrations of virions, which depend on factors such as the production rate, the outdoor airflow rate, and the mask factor.

## Summary & Key Takeaways

• The concentration of virions in the air per volume, determined by a mass balance in a well-mixed room, leads to the transmission of the virus from an infected person to a susceptible person.

• The transmission rate, beta, expresses the rate at which another person may become infected by breathing in infected droplets.

• The infectivity of an individual virion, combined with a mask factor, affects the probability that a susceptible person will get infected.