enter the lungs either by aspiration of contaminated water or inhalation of aerosolized contaminated water or soil. In the lung, the bacteria are consumed by macrophages, a type of white blood cell, inside of which the Legionella bacteria multiply, causing the death of the macrophage. Once the macrophage dies, the bacteria are released from the dead cell to infect other macrophages. Virulent strains of Legionella kill macrophages by blocking the fusion of phagosomes with lysosomes inside the host cell; normally, the bacteria are contained inside the phagosome, which merges with a lysosome, allowing enzymes and other chemicals to break down the invading bacteria. Diagnosis
People of any age may develop Legionnaires disease, but the illness most often affects middle-aged and older people, particularly those who smoke cigarettes or have chronic lung disease. Immunocompromised people are also at higher risk. Pontiac fever most commonly occurs in those who are otherwise healthy.The most useful diagnostic tests detect the bacteria in coughed-up mucus, find Legionella antigens in urine samples, or allow comparison of Legionella antibody levels in two blood samples taken 3–6 weeks apart. A urine antigen test is simple, quick, and very reliable, but only detects L. pneumophila serogroup 1, which accounts for 70% of disease caused by L. pneumophila, which means use of the urine antigen test alone may miss as many as 30% of cases. This test was developed by Richard Kohler in 1982.
Prevent stagnation, for example, by removing from a network of pipes any sections that have no outlet (dead ends). Where stagnation is unavoidable, as when a wing of a hotel is closed for the off-season, systems must be thoroughly disinfected just prior to resuming normal operation. Prevent the buildup of biofilm, for example, by not using (or by replacing) construction materials that encourage its development, and by reducing the quantity of nutrients for bacterial growth that enter the system. Periodically disinfect the system, by high heat or a chemical biocide, and use chlorination where appropriate. Treatment of water with copper-silver ionization or ultraviolet light may also be effective. System design (or renovation) can reduce the production of aerosols and reduce human exposure to them, by directing them well away from building air intakes.An effective water safety plan also covers such matters as training, record-keeping, communication among staff, contingency plans, and management responsibilities. The format and content of the plan may be prescribed by public health laws or regulations. To inform the water safety plan, the undertaking of a site specific legionella risk assessment is often recommended in the first instance. The legionella risk assessment identifies the hazards, the level of risk they pose and provides recommendations of control measures to put place within the overarching water safety plan. Treatment
Effective antibiotics include most macrolides, tetracyclines, ketolides, and quinolones. Legionella spp. multiply within the cell, so any effective treatment must have excellent intracellular penetration.