Legionellosis

Legionellosis

is an infectious disease caused by bacteria belonging to the genus Legionella.[1][2] Over 90% of legionellosis cases are caused by Legionella pneumophila, a ubiquitous aquatic organism that thrives in temperatures between 25 and 45 °C (77 and 113 °F), with an optimum around 35 °C (95 °F).[3]

Legionellosis takes two distinct forms:

Legionnaires' disease, also known as "Legion Fever"[4] (archaic), is the more severe form of the infection and produces pneumonia.[5]
Pontiac fever is caused by the same bacterium, but produces a milder respiratory illness without pneumonia which resembles acute influenza.[5]

Legionnaires' disease acquired its name in July 1976 when an outbreak of pneumonia occurred among people attending a convention of the American Legion in Philadelphia. On January 18, 1977 the causative agent was identified as a previously unknown bacterium, subsequently named Legionella.

An estimated 8,000 to 18,000 people get legionellosis in the United States each year.[3] Some people can be infected with the Legionella bacterium and have only mild symptoms or no illness at all.

Outbreaks of

Legionnaires' disease

receive significant media attention. However, this disease usually occurs as 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. The fatality rate of Legionnaires' disease has ranged from 5% to 30% during various outbreaks.

Legionellosis Symptoms

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, loss of coordination (ataxia), and occasionally diarrhea and vomiting. Laboratory tests may show that patients’ renal functions, liver functions and electrolytes are deranged, including hyponatremia. Chest X-rays often show pneumonia with bi-basal consolidation. It is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms or radiologic findings alone; other tests are required for diagnosis.

Persons with Pontiac fever experience fever and muscle aches without 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.

Infections

L. pneumophila is specifically considered as a pathogen of the respiratory tract. Other infections have also been reported, including haemodialysis fistulae, pericarditis and wound and skin infections. Bacteraemia is often associated with Legionnaires' disease. Intestinal infections may only occur as part of respiratory infections, and where gastrointestinal symptoms have on occasion been described.

No animal infections have been specifically recorded.

Infections of Protozoa such as Hartmannella 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. This pathway may be how these organisms survive in the environment[citation needed].

Legionellosis Diagnosis and treatment

People of any age may suffer from Legionnaires' disease, but the illness most often affects middle-aged and older persons, particularly those who smoke cigarettes or have chronic lung disease. Immunocompromised patients are also at elevated risk. Pontiac fever most commonly occurs in persons who are otherwise healthy.

The most useful diagnostic tests detect the bacteria in sputum, find Legionella antigens in urine samples, or the comparison of Legionella antibody levels to in two blood samples taken 3 to 6 weeks apart. A urine antigen test which is simple, quick, and very reliable will only detect Legionella pneumophila serogroup #1. In addition the urine antigen test will not identify the specific subtypes so it cannot be used to match the patient with the environmental source of infection.

Current treatments 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. Macrolides are used in all age groups while tetracyclines are prescribed for children above the age of 12 and quinolones above the age of 18.

Rifampicin can be used in combination with a quinolone or macrolide. Tetracyclines and erythromycin led to improved outcomes compared to other antibiotics in the original American Legion outbreak. These antibiotics are effective because they have excellent intracellular penetration and Legionella infects cells. The mortality at the original American 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.

According to the journal "Infection Control and Hospital Epidemiology," 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. [6]

Pontiac fever requires no specific antibiotic treatment.

Legionellosis
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On January 18, 1977 the causative agent was identified as a previously unknown bacterium, subsequently named Legionella. An estimated 8,000 to 18,000 people get legionellosis in the United States each year.[3] Some people can be infected with the Legionella bacterium and have only mild symptoms or no illness at all. Outbreaks of Legionnaires' disease receive significant media attention. However, this disease usually occurs as 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. The fatality rate of Legionnaires' disease has ranged from 5% to 30% during various outbreaks. Legionellosis Symptoms 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, loss of coordination (ataxia), and occasionally diarrhea and vomiting. Laboratory tests may show that patients’ renal functions, liver functions and electrolytes are deranged, including hyponatremia. Chest X-rays often show pneumonia with bi-basal consolidation. It is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms or radiologic findings alone; other tests are required for diagnosis. Persons with Pontiac fever experience fever and muscle aches without 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. Infections L. pneumophila is specifically considered as a pathogen of the respiratory tract. Other infections have also been reported, including haemodialysis fistulae, pericarditis and wound and skin infections. Bacteraemia is often associated with Legionnaires' disease. Intestinal infections may only occur as part of respiratory infections, and where gastrointestinal symptoms have on occasion been described. No animal infections have been specifically recorded. Infections of Protozoa such as Hartmannella 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. This pathway may be how these organisms survive in the environment[citation needed]. Legionellosis Diagnosis and treatment People of any age may suffer from Legionnaires' disease, but the illness most often affects middle-aged and older persons, particularly those who smoke cigarettes or have chronic lung disease. Immunocompromised patients are also at elevated risk. Pontiac fever most commonly occurs in persons who are otherwise healthy. The most useful diagnostic tests detect the bacteria in sputum, find Legionella antigens in urine samples, or the comparison of Legionella antibody levels to in two blood samples taken 3 to 6 weeks apart. A urine antigen test which is simple, quick, and very reliable will only detect Legionella pneumophila serogroup #1. In addition the urine antigen test will not identify the specific subtypes so it cannot be used to match the patient with the environmental source of infection. Current treatments 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. Macrolides are used in all age groups while tetracyclines are prescribed for children above the age of 12 and quinolones above the age of 18. Rifampicin can be used in combination with a quinolone or macrolide. Tetracyclines and erythromycin led to improved outcomes compared to other antibiotics in the original American Legion outbreak. These antibiotics are effective because they have excellent intracellular penetration and Legionella infects cells. The mortality at the original American 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. According to the journal "Infection Control and Hospital Epidemiology," 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. [6] Pontiac fever requires no specific antibiotic treatment.
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