Indoor Air sciences CSMI Practice Exam

Why is legionella not commonly found in outdoor air?

1. It likes growing in cooling towers which are indoors

2. It only grows indoors so it's uncommon to find it outdoors

3. It desiccates and is oxidized by outdoor air

4. It prefers humid outdoor conditions

The correct answer is: It desiccates and is oxidized by outdoor air

Legionella is a type of bacteria that thrives in specific environments often associated with human-made water systems, like cooling towers, hot tubs, and plumbing systems. The reason why it is not commonly found in outdoor air relates to its susceptibility to environmental conditions. Outdoor air exposes Legionella to factors like desiccation (drying out) and oxidation, which can significantly reduce its viability. In outdoor environments, ultraviolet (UV) radiation from sunlight and temperature fluctuations can be detrimental to bacterial survival. Additionally, the lack of stagnant water sources in outdoor air makes it hard for Legionella to thrive. Therefore, although some bacteria can be ubiquitous in outdoor environments, Legionella's specific biological needs for moist, warm environments, typically found indoors or in artificial water systems, mean that it does not commonly survive or proliferate in outdoor air. This context illustrates why desiccation and oxidation in outdoor settings would make it less likely to find Legionella in those areas.