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Legionellosis is an infection caused by species of the bacterium Legionella, most notably L. pneumophila. At least 46 species and 70 serogroups have been identified. L. pneumophila, an ubiquitous aquatic organism that thrives in warm environments (32°- 45°C) causes over 90% of Legionnaires Disease in the United States.
The disease has two distinct forms:
- Legionnaires' disease is the name for the more severe form of infection which includes pneumonia
- Pontiac fever is a milder respiratory illness without pneumonia caused by the same bacterium
Legionnaires' disease acquired its name in 1976 when an outbreak of pneumonia occurred among persons attending a convention of the American Legion in Philadelphia. Later, the bacterium causing the illness was named Legionella.
An estimated 8,000 to 18,000 people get Legionnaires' disease in the United States each year. Some people can be infected with the Legionella bacterium and have mild symptoms or no illness at all.
Outbreaks of Legionnaires' disease receive significant media attention. However, this disease usually occurs as a single, isolated case not associated with any recognized outbreak. When outbreaks do occur, they are usually recognized in the summer and early fall, but cases may occur year-round. About 5% to 30% of people who have Legionnaires' disease die.
What are the usual symptoms of legionellosis?
Patients with Legionnaires' disease usually have fever, chills, and a cough, which may be dry or may produce sputum. Some patients also have muscle aches, headache, tiredness, loss of appetite, and, occasionally, diarrhea. Laboratory tests may show that these patients' kidneys are not functioning properly. Chest X-rays often show pneumonia. It is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms alone; other tests are required for diagnosis.
Persons with Pontiac fever experience fever and muscle aches and do not have pneumonia. They generally recover in 2 to 5 days without treatment.
The time between the patient's exposure to the bacterium and the onset of illness for Legionnaires' disease is 2 to 10 days; for Pontiac fever, it is shorter, generally a few hours to 2 days.
Intestinal Infections: These may only occur as part of respiratory infections, where gastrointestinal symptoms have on occasion been described.
Extraintestinal Infections: L. pneumophila is specifically considered as a pathogen of the respiratory tract, where it is a cause of atypical pneumonia, also known as Legionnaires' disease. Other infections have also been reported, including haemodialysis fistulae , pericarditis and wound and skin infections. Bacteraemia is often associated with Legionnaires' disease.
Animal Infections: None specifically recorded. Infections of Protozoa: Protozoa such as Harmanella vermiformis and related protozoa have been shown to be able to support the growth of L. pneumophila in tap water. Also Acanthamoeba, Naegleria and Tetrahymena can be infected by L. pneumophila. It is considered that this may be how these fastidious organisms survive in the environment.
How is legionellosis diagnosed?
The diagnosis of legionellosis requires special tests not routinely performed on persons with fever or pneumonia. Therefore, a physician must consider the possibility of legionellosis in order to obtain the right tests.
Several types of tests are available. The most useful tests detect the bacteria in sputum, find Legionella antigens in urine samples, or compare antibody levels to Legionella in two blood samples obtained 3 to 6 weeks apart.
Who gets legionellosis?
People of any age may get Legionnaires' diasease, but the illness most often affects middle-aged and older persons, particularly those who smoke cigarettes or have chronic lung disease. Also at increased risk are persons whose immune system is suppressed by diseases such as cancer, kidney failure requiring dialysis, diabetes, or AIDS. Those that take drugs that suppress the immune system are also at higher risk.
Pontiac fever most commonly occurs in persons who are otherwise healthy.
Treatment of legionellosis
The current treatment of choice are the respiratory tract quinolones (levofloxacin, moxifloxacin, gemifloxacin) or newer macrolides (azithromycin, clarithromycin, roxithromycin). The antibiotics used most frequently have been levofloxacin and azithromycin. Rifampin can be used in combination with with a quinolone or macrolide. Tetracyclines and erythromycin led to improved outcome compared to other antibiotics in the original American Legion outbreak. These antibiotics are effective because they have excellent intracellular penetration since legionella infects cells. The mortality at original 1976 Anerican Legion convention in 1976 was high (34 deaths in 180 infected individuals) because the antibiotics used including penicillins, cephalosporins, and aminoglycosides had poor intracellular penetration. Mortality has plunged to less than 5% if therapy is started quickly. Delay in giving the appropriate antibiotic leads to higher mortality.
How is legionellosis spread?
Legionellosis infection occurs after persons have breathed mists that come from a water source (e.g., air conditioning cooling towers, whirlpool spas, showers) contaminated with Legionella bacteria. Persons may be exposed to these mists in homes, workplaces, hospitals, or public places. Legionellosis is not passed from person to person, and there is no evidence of persons becoming infected from auto air conditioners or household window air-conditioning units.
Legionella Longbeachae, one species in the Legionella family, is found in soils, and compost. Persons inhaling soil or compost dust containing Legionella Longbeachae risk contracting Legionnaires' Disease.
Where is the Legionella bacterium found?
Legionella organisms can be found in many types of water systems. However, the bacteria reproduce to high numbers in warm, stagnant water (90°-105° F, 32°-40° C), such as that found in certain plumbing systems and hot water tanks, cooling towers and evaporative condensers of large air-conditioning systems, and whirlpool spas. Cases of legionellosis have been identified throughout the United States and in several foreign countries. It is believed to occur worldwide.
What is being done to prevent legionellosis?
Improved design and maintenance of cooling towers and plumbing systems to limit the growth and spread of Legionella organisms are the foundations of legionellosis prevention.
During outbreaks, CDC and health department investigators seek to identify the source of disease transmission and recommend appropriate prevention and control measures, such as decontamination of the water source. Current research will likely identify additional prevention strategies.
World's more important outbreaks
In March, 1999 an outbreak in the Netherlands occurred during a flower exhibition in Bovenkarspel. 200 people became ill and at least 32 people died. Probably more people died, but these were buried before the Legionella infection was recognized. The source of the bacteria were probably a whirlpool and a moisturizer in the exhibition area.
The world's largest outbreak of legionnaries' disease happened in July 2001 (the patients began to go to the hospital on July 7), in Murcia, Spain, where more than 800 suspected cases were recorded by July 22, when the last case was treated; 636–696 of these cases were estimated and 449 confirmed (so, at least 16,000 persons were exposed to the bacterium) and 6 dead (this is, a case-fatality rate of aprox. 1%.).
A case-control study matching 85 patients living outside the city of Murcia with two controls each was undertaken to identify the outbreak source; the epidemiologic investigation implicated the cooling towers at a city hospital (Morales Meseguer Hospital). An environmental isolate from these towers with an identical molecular pattern as the clinical isolates was subsequently identified and supported that epidemiologic conclusion.
In September 2004, it was revealed in an article in the magazine "Science" that the complete genome of Legionella pneumophila has been unraveled. This will help researchers to find out how exactly the bacterium works and how people can be protected against infection.
- Harrison's textbook of medicine and Mandell's infectious disease textbook (5th edition), New Engl J Med 1997
- Legionella.org by Victor L Yu, Pofessor of Medicine at the University of Pittsburgh.
- Legionella; Murcia- Spain 28th June to 14th July 2001; the world's largest outbreak of legionnaries'disease.
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