Fig. 1

Humans naturally emit 30 million microbial cells per hour, which could combine and get stabilized with water particles naturally found in the humid air surrounding us. These microbial emissions can spread through the air in the built environment. By using a small surface cooled below the dew point, water-dispersed samples can be collected (right), which, in principle, would also contain DNA emitted by the human source. Thus, analysis of the collected condensate can provide a measure of the risk posed by the airborne presence of such particles