Legionella species

The genus Legionella is a pathogenic group of Gram-negative bacteria that includes the species L. pneumophila, causing legionellosis (all illnesses caused by Legionella) including a pneumonia-type illness called Legionnaires' disease and a mild flu-like illness called Pontiac fever. It's quite common to find Legionella species other than Legionella pneumophila in cooling towers and water distribution systems. To date, more than 58 Legionella species have been described in published articles. Of these species, approximately 25 are linked to diseases, such as Legionella pneumophila species serogroup 1, 3, 4, and 6. Legionella pneumophila serogroup 1 is the most virulent strain resulting in a majority of infections. The remaining non-pneumophila species (found in water and soil) were considered nonpathogenic until shown to cause diseases. Of the CDC reported cases, less than 5% is attributed to non-pathognenic species. Since the risk for infection is tiny, it's reasonable to adjust your response to an adequate threat level.