Legionnaires' disease is a form of pneumonia caused by the legionella bacterium. It is usually transmitted through inhalation of the bacteria in mist from air conditioning units, hot tubs and showers, according to MedlinePlus, but it typically cannot be contracted through direct contact with an infected person. Individuals who are older, smoke, have weakened immune systems or suffer from lung disease are more susceptible to the infection.
The legionella bacterium exists mainly in soil yet rarely infects anyone outdoors, explains Mayo Clinic. Indoors, it multiplies in water systems, including grocery store mist sprayers. Generally, the disease occurs more frequently in large buildings.
Early symptoms such as high fever, chills, headache and myalgia typically occur 2 to 10 days after exposure to legionella bacteria, according to Mayo Clinic. Within 24 to 48 hours after the onset of initial symptoms, patients usually experience symptoms such as cough, chest pain, confusion, nausea, diarrhea, vomiting, confusion and shortness of breath.
Legionella usually affects the lungs, but it may also infect wounds and the heart, according to Mayo Clinic. It is diagnosed via a urine antigen test or blood tests and treated with antibiotics. The disease can lead to complications such as septic shock or respiratory and kidney failure. Outbreaks are preventable if pools, spas and water systems are cleaned and disinfected properly.