"Relative bradycardia" may also be present, which is low to normal heart rate despite the presence of a fever.Laboratory tests may show that kidney functions, liver functions, and electrolyte levels are abnormal, which may include low sodium in the blood. Chest X-rays often show pneumonia with consolidation in the bottom portion of both lungs. Distinguishing Legionnaires disease from other types of pneumonia by symptoms or radiologic findings alone is difficult; other tests are required for definitive diagnosis.People with Pontiac fever, a much milder illness caused by the same bacterium, experience fever and muscle aches without pneumonia. They generally recover in 2–5 days without treatment. For Pontiac fever, the time between exposure and symptoms is generally a few hours to two days. Cause
Over 90% of cases of Legionnaires disease are caused by Legionella pneumophila. Other types include L. longbeachae, L. feeleii, L. micdadei, and L. anisa. Transmission
Legionnaires disease is usually spread by the breathing in of aerosolized water or soil contaminated with the Legionella bacteria. Experts have stated that Legionnaires disease is not transmitted from person to person. In 2014, one case of possible spread from someone sick to the caregiver occurred. Rarely, it has been transmitted by direct contact between contaminated water and surgical wounds. The bacteria grow best at warm temperatures and thrive at water temperatures between 25 and 45 °C (77 and 113 °F), with an optimum temperature of 35 °C (95 °F). Temperatures above 60 °C (140 °F) kill the bacteria.
Hospital-acquired Legionella pneumonia has a fatality rate of 28%, and the principal source of infection in such cases is the drinking-water distribution system. Epidemiology
Legionnaires disease acquired its name in July 1976, when an outbreak of pneumonia occurred among people attending a convention of the American Legion at the Bellevue-Stratford Hotel in Philadelphia. Of the 182 reported cases, mostly men, 29 died. On 18 January 1977, the causative agent was identified as a previously unknown strain of bacteria, subsequently named Legionella, and the species that caused the outbreak was named Legionella pneumophila. Following this discovery, unexplained outbreaks of severe respiratory disease from the 1950s were retrospectively attributed to Legionella. Legionnaires disease also became a prominent historical example of an emerging infectious disease.Outbreaks of Legionnaires disease receive significant media attention, but this disease usually occurs in single, isolated cases not associated with any recognized outbreak. When outbreaks do occur, they are usually in the summer and early autumn, though cases may occur at any time of year. Most infections occur in those who are middle-aged or older. National surveillance systems and research studies were established early, and in recent years, improved ascertainment and changes in clinical methods of diagnosis have contributed to an upsurge in reported cases in many countries. Environmental studies continue to identify novel sources of infection, leading to regular revisions of guidelines and regulations.