In a new study, researchers have found that light rain can cause some disease-causing bacteria in dry soil to spread far and wide. At temperatures similar to that in the tropical regions, when rain falls at the speed of a light rain, a spray of mist called aerosols is released. This spray carries thousands of bacteria from the soil with it. The bacteria thus dispersed can stay alive for more than an hour. Wind could further transport these disease-causing bacteria to distant places.
About 1%-25% of the total amount of bacteria is emitted from land through precipitation. Researchers have found that even sprinklers can have the same affect and contribute to dispersal of pathogenic bacteria.
As rain droplets touch the ground, they trap tiny air bubbles at the ground's surface. These bubbles rise up and burst through the droplet, creating a spray of much smaller water droplets, or aerosols. This mechanism may also explain the characteristic earthy smell after rainfall called petrichor.
Scientists particularly studied Burkholderia pseudomallei, a bacterium that lives in soil and is known to cause lung infections in humans. What triggered the scientists to conduct this study was the correlation between the number of cases of this disease and rainfall. The number went up after rainfall. This helped them to study rain as a possible disperser of bacteria.