[Occurrence and pathogenicity of the family of Legionellaceae]

Legionella are widespread in natural aquatic environments and are able to exist in water of different temperatures, pH level, and nutrient and oxygen content. Their occurrence in nature can be attributed to their relationships with other microorganisms. When Legionella co-exist with algae and other bacteria, especially in biofilms, the availability of nutrients increases. They also are able to infect protozoa and subsequently reproduce within these organisms. As a result of these relationships, Legionella are protected against adverse conditions, including standard water disinfection techniques. Consequently, they are also prevalent in anthropogenic water such as drinking water, whirlpools, and cooling tower reservoirs. Aerosol-generating systems aid in the transmission of Legionella from water to the air. Human inhalation of contaminated aerosols leads to Legionella infection and disease outbreaks. Legionellosis in humans has typically been characterized as either a potentially fatal pneumonic condition, known as Legionnaires' disease, or an acute, self-limiting, non-pneumonic condition known as Pontiac fever. In addition, Legionella spp. cause extrapulmonary infection, especially in immunosuppressed patients. Timely treatment of Legionnaires' disease is extremely important for the patient's recovery. Although erythromycin has historically been used to treat patients with Legionnaires' disease, newer macrolides and fluoroquinolones are gaining acceptance as the first choice for treatment. Although 52 species of Legionella are known, Legionella pneumophila serogroup 1 is responsible for more than 80% of hospital- and community-acquired cases of Legionnaires' disease.