Legionnaires disease

Serious, sometimes lethal pneumonia or influenza like self-limited illness (Pontiac fever).

Caused by Legionella bacteria.

Legionella gram-negative, facultative, intracellular bacteria with water and soil environmental reservoirs.

Humans acquire legionella through inhalation of contaminated aerosols.

The incidence of legionellosis is six times as high as it was two decades ago and is due to improved diagnostic capabilities, an aging infrastructure and population, and rising global temperatures resulting in a warmer, weather climate.

Incidence 1.15 per hundred thousand persons has been increasing.

Risk factors for Legionella pneumonia include: male gender, age greater than 50 years, cigarette smoking, impaired immunity, neuromuscular disease, occupational exposure to engineered water systems such as cooling towers, hot tubs, showers, and decorative fountains.

Increased incidence with age.

Males account for more than 60% of cases.

Most cases occur in the late spring or early fall.

The incubation period is 2–10 days.

There is a mildly increased incidence in northern states.

The bacterium is one or 42 species constituting 64 serogroups.

It is a small, and Gram negative, catalase positive, weekly oxidase positive, aerobic, waterborne bacterium that is non-motile and often lives in symbiosis with various amoebic species that are common residents of water rich environments.

Engineered water systems are reservoirs for legionella.

Engineered water systems are reservoirs for legionella.

Engineered water systems favor the proliferation of legionella when temperatures are between 25° centigrade and 43°C, are stagnant, have increased levels of organic matter, and plumbing biofilms.

The presence of turbulence in water flow at distal water sources facilitates transmission of legionella to humans through contaminated aerosols.

Healthcare facilities are potential legionella reservoirs due to their complex plumbing and vulnerable populations with about 20% of cases in the US acquired nosocomially.

Water-rich environment include: cooling systems, showers, decorative fountains, humidifiers, whirlpool spas, and other structures in which bacteria can survive in an optimal temperature.

Infections often occur through inhalation aerosol as particles or via aspiration of contaminated liquid

Typically not transferable from human to human.

Blacks account for a disproportionate number of cases.

Increase number of cases during the summer and early fall.

8-18,000 persons are hospitalized each year for Legionnaires disease.

Urine antigen tests for Legionella pneumophila has the sensitivity of 60 to 80%, and a specificity of greater than 99% for this causative agent of 70 to 80% of cases.

Because urinary antigen testing has a limited diagnostic sensitivity of only 75%, the worldwide burden of legionnaires disease is estimated to be up to 10 times as high as the number of cases reported.

PCR testing for legionella is preferred as you can detect all clinically relevant legionella sub groups and species.

Legionella grows poorly and routine culture medium and diagnosis is relied upon by urinary antigen testing.

Culture a respiratory secretions from possible LD cases has a sensitivity of 20 to 80%, and a specificity of greater than 99% to detect all forms of Legionella.

Associated with living in poverty, older age, working outdoor jobs with machinery or in cleaning services are primary risk factors in New York City (Farnham et al ).

Associated with smoking and diabetes mellitus.

Concurrent G.I. symptoms of nausea and diarrhea and laboratory findings of hyponatremia, elevated liver functions, and elevated creatinine phosphokinase are frequently reported in patients with legionella pneumonia, but these findings are not discriminatory from other pathogens.

Imaging studies include x-ray evidence of bacterial pneumonia, especially in an immunocompromised patient.

First line treatment of Legionella pneumonia is either azithromycin or levofloxacin.

Combination antimicrobial therapy is frequently used for severe disease without supporting data of advocacy.

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