Legionnaires disease: Description:Also called: Legionellosis.Alternative Name: Legionella pneumonia; Pontiac fever.Legionnaires diseaseAn acute infectious disease, caused by Legionella pneumophila, with prodromal influenza like symptoms and a rapidly rising high fever, followed by severe pneumonia and production of usually nonpurulent sputum, and sometimes mental confusion, hepatic fatty changes, and renal tubular degeneration. It has a high case-fatality rate; acquired from contaminated water, usually by aerosolization rather than being transmitted from person-to-person.It is estimated that approximately 10,000 to 15,000 people contract Legionnaires' disease in the United States each year. An additional unknown number of people are infected with the Legionella bacterium but have only mild symptoms or no symptoms at all.Outbreaks of Legionnaires' disease have received the most media attention. However, the disease most often occurs as single, isolated cases not associated with any identified outbreak. Outbreaks are usually recognized in the summer and early fall, but cases may occur year-round. About 5%-15% of known cases of Legionnaires' disease have been fatal.Since the bacterium of Legionnaires' disease was identified in 1976, numerous hospital-acquired outbreaks of the disease have been reported. These outbreaks have enabled researchers to study epidemics of legionellosis.People of any age can develop Legionnaires' disease, but the illness most often affects middle-aged and older people, particularly those who smoke cigarettes or have chronic lung disease, as these individuals have a greater likelihood of developing any respiratory illness.People at an increased risk for Legionnaires' disease also include people whose immune systems are suppressed by diseases such as cancer, kidney failure requiring dialysis, diabetes, or AIDS. Those who take medications that suppress the immune system are also at risk.Symptoms:Legionellosis is associated with two distinct illnesses: Legionnaires' disease, which is characterized by fever, myalgia, cough, pneumonia, and Pontiac fever, a milder illness without pneumonia.Legionnaires' disease has an incubation period (the time from exposure to the onset of symptoms) of 2 to 10 days. Severity ranges from a mild cough and low fever to rapidly progressive pneumonia, coma, and death. Not all individuals with Legionnaires' disease experience the same symptoms.Early symptoms include slight fever, headache, aching joints and muscles, lack of energy or tiredness, and loss of appetite.Later symptoms include:High fever (102° to 105° F, or 39° to 41° C).
  • Cough (dry at first, later producing phlegm).
  • Difficulty in breathing or shortness of breath.
  • Chills.
  • Chest pain.
Pontiac fever is a non-pneumonia disease with a short incubation period of one to three days. Full recovery usually occurs in two to five days without medical intervention and no deaths have been reported. Pontiac fever produces flu-like symptoms that may include fever, headache, tiredness, loss of appetite, muscle and joint pain, chills, nausea, and a dry cough.Causes and Risk factors:Legionnaires' disease is caused by inhaling Legionella bacteria from the environment. Typically, the bacteria are dispersed in aerosols of contaminated water. These aerosols are produced by devices in which warm water can stagnate, such as air-conditioning cooling towers, humidifiers, shower heads, and faucets. There have also been cases linked to whirlpool spa baths and water misters in grocery store produce departments. Aspiration of contaminated water is also a potential source of infection, particularly in hospital-acquired cases of Legionnaires' disease. There is no evidence of person-to-person transmission of Legionnaires' disease.The bacteria that cause Legionnaires' disease are found in warm, stagnant water and the soil it seeps into. People inhale the bacteria when it becomes airborne, usually through air conditioners, humidifiers, shower heads and faucets, whirlpool spas, and even the water misters found in grocery stores. The bacteria has also been found in soil and groundwater at construction sites. Some people can be exposed to the Legionella bacteria, but not develop the infection.Once the bacteria are in the lungs, cellular representatives of the body's immune system (alveolar macrophages) congregate to destroy the invaders. The typical macrophage defense is to phagocytose the invader and demolish it in a process analogous to swallowing and digesting it. However, the Legionella bacteria survive being phagocytosed. Instead of being destroyed within the macrophage, they grow and replicate, eventually killing the macrophage. When the macrophage dies, many new Legionella bacteria are released into the lungs and worsen the infection.Legionnaires disease develops 2-10 days after exposure to the bacteria. Early symptoms include lethargy, headaches, fever, chills, muscle aches, and a lack of appetite. Respiratory symptoms such as coughing or congestion are usually absent. As the disease progresses, a dry, hacking cough develops and may become productive after a few days. In about a third of Legionnaires disease cases, blood is present in the sputum. Half of the people who develop Legionnaires disease suffer shortness of breath and a third complain of breathing-related chest pain. The fever can become quite high, reaching 104°F (40°C) in many cases, and may be accompanied by a decreased heart rate.From the onset of symptoms, the condition typically worsens during the first 4 to 6 days, with improvement starting in another 4 to 5 days. Most infection occurs in middle-aged or older people, although it has been reported in children. Typically, the disease is less severe in children.Risk factors include cigarette smoking; underlying diseases such as renal failure, cancer, diabetes, or chronic obstructive pulmonary disease; people with suppressed immune systems from chemotherapy, steroid medications, or diseases such as cancer and leukemia; alcoholism; being middle-aged or elderly, and in people on a ventilator for extended periods.Diagnosis:Legionnaires disease is difficult to diagnose because the pneumonia caused by LDB is not easily distinguished from other forms of pneumonia.The Centers for Disease Control and Prevention (CDC) defines a confirmed case of Legionnaires disease as a clinically compatible case that is confirmed by a laboratory. A confirmed case requires a physician's diagnosis of pneumonia based on a chest x-ray and positive laboratory test results. A laboratory test is necessary for confirmation because the symptoms and x-ray evidence of Legionnaires' disease resemble those of other types of pneumonia.The CDC laboratory criteria for diagnosis are:
  • Isolation of LDB from respiratory secretions, lung tissue, pleural fluid, or other normally sterile fluids.
  • Demonstration of a fourfold or greater rise in the reciprocal immunofluorescence antibody (IFA) titer to greater than or equal to 128 against Legionella pneumophila serogroup 1 between paired acute- and convalescent-phaseserum specimens.
  • Detection of L. pneumophila serogroup 1 in respiratory secretions, lung tissue, or pleural fluid by direct fluorescent antibody testing,
  • Demonstration of L. pneumophila serogroup 1 antigens in urine by radioimmunoassay or enzyme-linked immunosorbent assay.
Laboratory Studies:
  • CBC: Look for leukocytosis, left shift, hematologic malignancy, and disseminated intravascular coagulation (DIC).
  • Electrolytes: Look for hyponatremia, since syndrome of inappropriate secretion of antidiuretic hormone (SIADH) has been associated with this disease.
  • BUN and creatinine: Look for renal failure and dehydration.
  • Liver function tests (LFTs): Look for nonspecific LFT abnormalities, which are very common in this disease and may help distinguish Legionnaires disease from other pneumonias.
  • Alkaline phosphatase: Look for nonspecific depression, which along with LFT abnormalities is very common.
  • Creatine phosphokinase: Look for elevation indicating rhabdomyolysis, which occasionally is seen in Legionnaires disease. The rhabdomyolysis may be so severe as to cause renal failure.
  • Urinalysis: Look for proteinuria, hematuria, and renal failure.
  • Sputum Gram stain: Look for increased polymorphonuclear leukocytes and monocytes without bacteria.
  • Sputum and blood cultures: Although no findings will return to the ED, this will assist consultants caring for the patient. Respiratory culture specifically for Legionella (buffered charcoal yeast extract agar [BCYE]) may be indicated.
  • ABG: Look for hypoxemia.
  • Polymerase chain reaction (PCR) testing has been used in the past, although its role in current diagnosis and practice has yet to be established
  • Serology for Legionella species: Several tests are available.
  • Acute and convalescent sera (at 8-12 wk) demonstrating a 4-fold increase in titer to >1/128 must be present for serological diagnosis.
  • Urine antigen testing is highly specific and sensitive and, if available within the treatment facility, very rapid.
  • Indirect fluorescent antibody testing and nucleic acid hybridization testing also may be available.
  • Direct fluorescent antibody examination has fallen out of favor.
Imaging Studies:Chest radiography: Legionella infection almost always produces an abnormal chest radiographic finding, but abnormality is variable and may be focal or diffuse, up to 50% of patients have a pleural effusion.Chest radiography is not a specific test for Legionnaires disease.Chest radiograph often shows patchy alveolar infiltrates with consolidation in the lower lobe (although all lobes may be affected).It may take 1-4 months for the chest radiographic finding to return to normal.Noncontrast head CT scan: This is indicated for patients with altered mental status.Other Tests: Silver and Gimenez stains for lung tissue/specimensTreatment:The goal of treatment for Legionnaires disease is to eliminate the infection with antibiotics. Treatment is started as soon as Legionnaire's disease is suspected, without waiting for confirmation by culture results. Most cases of Legionella pneumonia show improvement within 12-48 hours of starting antibiotic therapy. The antibiotic of choice has been erythromycin, sometimes paired with a second antibiotic, rifampin. Tetracycline, alone or with rifampin, is also used to treat Legionnaires disease, but has had more mixed success in comparison to erythromycin. Other antibiotics that have been used successfully to combat Legionella include doxycycline, clarithromycin, fluorinated quinolones, and trimethoprim/sulfamethoxazole. The type of antibiotic prescribed by the doctor depends on several factors including the severity of infection, potential allergies, and interaction with previously prescribed drugs. For example, erythromycin interacts with warfarin, a blood thinner. supportive treatment includes hospitalization for fluid and electrolyte replacement and oxygen administration by mask or by mechanical ventilation, if the respiratory system becomes severely compromised by the infection.Medicine and medications:There are three major classes of antibiotics that are effective in treating legionellosis. These include the fluoroquinolones such as ciprofloxacin (Cipro), levofloxacin (Levaquin), and moxifloxacin (Avelox), the macrolides such as erythromycin, azithromycin (Zithromax), and clarithromycin (Biaxin), and the tetracyclines including doxycycline (Vibramycin). The choice of antibiotic is often dependent on the patient's clinical state, tolerance to the medication, and degree of certainty as to the diagnosis.In severe cases of Legionnaires disease that seem more resistant to a single antibiotic, a second drug called rifampin may be added.DISCLAIMER: This information should not substitute for seeking responsible, professional medical care. 


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