1-Virus spreads through air especially indoor in areas of low ventialtion
Have a look at this thread if you want to know how you can check if ventialtion in an area is adequate.
Its really easy!
2-Every time you exhale CO2 is exhaled in air. You can use CO2 levels to see if room is filling with potentially infectious exhalations
CO2 level lets you estimate if enough fresh outside air is getting in
3-Last year in Taiwan tuberculosis outbreak at Taipei University was found out to be due to underventilated rooms. Rooms had CO2 levels⬇️3000 ppm.When air circulation was improved with CO2 levels⬇️600 ppm outbreak completely stopped