American Journal of Critical Care. 2003;12: 234-238
Journal Club Feature
Legionnaires Disease: A Case Study
By
Melinda Cramer, RN, BSN.
From
School of Nursing, University of Pennsylvania, Philadelphia, Pa.
Legionella pneumophila, an aerobic, gram-negative bacillus, is 1 of the top 3 causes of community-acquired pneumonia,1 accounting for 3% to 15% of all cases.2 According to estimates from the Centers for Disease Control and Prevention, although 18 000 to 25 000 cases of pneumonia due to this organism occur each year, the diagnosis is reported in only 1200 to 1500 cases because of the nonspecific signs and symptoms of the disease and inadequate testing for Legionella.3 High mortality is associated with pneumonia caused by L pneumophila, especially in patients who are immunocompromised. This case study presents information about the epidemiology, pathophysiology, clinical features, and treatment of legionnaires disease and emphasizes the importance of early diagnosis.
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Case Study
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A 28-year-old man, N.C., came to the emergency department because he had shortness of breath, fatigue, a cough, diarrhea, and arthralgias. The shortness of breath was associated with minimal exertion (1 flight of stairs) and resolved after several minutes of rest. He did not have pain on inspiration or chest pain. He described the fatigue as overwhelming, and his activities were restricted to essential activities of daily living. The cough was nonproductive and did not have a pattern or aggravating or relieving factors. It was not associated with pain, positioning, or time of day. One day before admission, he had had fever and chills, with a maximum body temperature of 38.6°C (101.4°F). Watery, brown diarrhea occurred without other gastrointestinal distress and was intermittent, approximately 7 to 8 times a day. No treatments had been instituted at home.
N.C. had had idiopathic dilated cardiomyopathy in 1990 and had received an orthotopic heart transplant in 1994. Other notable abnormalities and previous interventions included transplant arteriopathy, biventricular heart dysfunction, placement of a pacemaker, recurrent right-sided pleural effusions, pleurodesis, posttransplant hypertension, hypercholesterolemia, treatment with antibodies to cardiolipin, a thoracotomy, chronic renal insufficiency, and coronary artery disease. His name was again on the list for a heart transplant, status 1B. At the time of admission, he was taking intravenous milrinone, warfarin, furosemide, antihypertensives, and drugs to prevent rejection of his heart transplant. He had a brother who also had received a heart transplant because of idiopathic dilated cardiomyopathy.
N.C. did not use alcohol or tobacco. He lived in an apartment with 2 roommates and worked at home as an editor. He had no pets and he had not traveled recently, but both roommates had had an upper respiratory infection within the preceding week.
In the emergency department, N.C. was afebrile and mildly short of breath, with respirations 18/min, blood pressure 90/40 mm Hg, and heart rate 110/min. Cardiac rhythm was sinus tachycardia. Arterial oxygen saturation was 84% when he was breathing room air and increased to 95% when he was breathing 50% oxygen via a face mask. Jugular venous distension was present at the angle of the jaw. Rales were present in one third of the lung fields bilaterally. Percussion revealed dullness at the base of the right lung. Cardiac assessment revealed a regular rhythm with a hyperdynamic point of maximum impulse; S1, S2, and S3 heart sounds; and a grade III/VI tricuspid murmur. He had 1+ edema in the lower extremities and 2+ pedal pulses. Neurologically, he had no focal deficits, and he followed commands appropriately. The results of an abdominal assessment were unremarkable. He had no clubbing of the fingers or cyanosis.
Tests of blood samples obtained in the emergency department indicated the following serum levels: sodium 131 mmol/L, potassium 4.6 mmol/L, chloride 107 mmol/L, urea nitrogen 7.1 mmol/L (20 mg/dL), and creatinine 115 µmol/L (1.3 mg/dL). A complete blood cell count was as follows: white blood cell count 16.8 x 109/L and platelet count 319 x 109/L. His hemoglobin level was 88 g/L, and his hematocrit was 0.26. The serum level of thyrotropin was 2.45 mIU/L. Blood levels of digoxin, cyclosporine, and mycophenolate (CellCept) were appropriate. A chest radiograph showed bilateral diffuse basilar infiltrates, otherwise unchanged from findings on previous radiographs. All cultures of blood, stool, and sputum; tests to detect acid-fast bacilli; assays of nasal swabs for detection of influenza viruses A and B; and urine test for Legionella antigen were pending.
N.C. was admitted to the cardiac intermediate care unit for further observation and treatment. Small doses of diuretics were given for fluid overload, previous medications were continued, and administration of levofloxacin was started.
On hospital day 3, N.C. was less short of breath than before, but he continued to have a nonproductive cough. His vital signs were body temperature 37.8°C (99.9°F), heart rate 78/min, blood pressure 96/50 mm Hg, and respirations 16/min. He was weaned from 50% oxygen via a face mask to 2 L of oxygen by nasal cannula; oxygen saturation by pulse oximetry was 96%. The diarrhea had improved. His electrolyte levels were unremarkable, but his white blood cell count increased to 26.0 x 109/L. The cultures for influenza A and B viruses were negative as were stool cultures for ova and parasites and blood cultures for bacteria and fungus. The urine test for Legionella antigen was positive. The infectious disease team recommended that levofloxacin 500 mg orally once a day be continued for a total of 14 days. Samples of material from a humidifier from N.C.’s apartment were cultured as a potential source of the Legionella.
N.C. showed clinical improvement and was discharged on hospital day 8. He was taking all of his previous medications and would continue to take levofloxacin to complete the 14-day course of treatment. His white blood cell count had decreased to 15.2 x 109/L, and his final chest radiograph showed bilateral patchy infiltrates compatible with pneumonia. He was afebrile and had stable vital signs, including an oxygen saturation of 99% when he was breathing room air.
The patient was scheduled to have a follow-up appointment, as well as another chest radiograph and laboratory tests (including a complete blood cell count, blood chemistries, and measurement of levels of immunosuppressant medications) 10 days after discharge. He was not to return to his home until the cultures of the samples from the humidifier were known to be negative for Legionella. The culture was negative, and the source of Legionella was not ascertained.
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Discussion
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Legionnaires disease was first described after an outbreak in 1976 in Philadelphia at the American Legion convention. Several outbreaks and numerous individual cases have occurred since. The disease is due to L pneumophila, which causes an atypical pneumonia. The natural habitat for L pneumophila is fresh water or protozoan biofilms, in which the bacteria parasitize and proliferate inside the protozoa.4 Within the natural aquatic environment, the concentrations of L pneumophila are relatively low. Once the water is transferred into man-made water reservoirs, the Legionella organisms proliferate because of favorable conditions (Table 1
). Warmer temperatures, stagnation, presence of other organisms, and scale and sediment lead to increased concentrations of L pneumophila.5 Legionella is transmitted to humans via inhalation of colonized aerosols or droplets, which are produced by air conditioners, cooling towers and condensers, water fountains, shower heads, faucets, whirlpools, ice machines, spas, nebulizers, and humidifiers.6
The incidence of legionnaires disease depends on several factors. The concentration of L pneumophila in aerosols or droplets, the immune susceptibility of the person exposed, and the time and intensity of the exposure are all contributory.7 Associated risk factors include advanced age, immunocompromised state, cigarette smoking, chronic lung disease, and male sex.1 Postoperative patients and transplant recipients are also at increased risk.
Pathophysiology
Once inhaled, L pneumophila adheres to the respiratory tract by means of pili that ensure attachment and prevent dislocation by mucociliary clearance.2 Conditions that cause damage to the respiratory cilia, such as smoking, alcohol consumption, and lung disease, increase the rate of infection by L pneumophila.2 The immune system mounts a cell-mediated reaction in which macrophages attach to the outer walls of the bacteria for active phagocytosis. The engulfed bacteria proliferate within the macrophages.8 As phagocytosis continues, some of the bacteria are eradicated, but a significant number replicate until the macrophage lyses. As the bacteria are released from the newly lysed cell, more macrophages begin the process of phagocytosis, and the cycle continues.8 A humoral immune reaction (IgM and IgG antibodies) also occurs2 (see Figure).
Clinical Manifestations
The clinical manifestations of legionnaires disease are summarized in Table 2. The signs and symptoms are nonspecific and are similar to those of an atypical pneumonia, but more severe. The incubation period is 2 to 10 days9; during this time, the signs and symptoms are typically mild. Initial signs and symptoms are generalized malaise, chills, fevers, headaches, arthralgias, and a non-productive cough.10 Gastrointestinal distress is common and is characterized by nausea, vomiting, and watery diarrhea.10 If the disease is untreated, it may progress to neurological disturbances ranging from lethargy and confusion to a comatose state or stupor. Multiple systems can be affected. Liver dysfunction, renal dysfunction, and hematologic disturbances have been associated with progression of legionnaires disease.
Examination of the lungs may initially reveal focal rales that will eventually become diffuse. Findings on an initial radiograph of the chest may be normal, but eventually a pulmonary infiltrate will develop.11
Diarrhea is common in legionnaires disease, and usually hyponatremia occurs because of the loss of sodium and water. Other abnormalities include elevated serum levels of liver enzymes, hypophosphatemia, thrombocytopenia, hematuria, and moderate elevation of serum levels of creatine kinase.11
Diagnosis
Four tests are predominantly used to detect the presence of Legionella: culture of specimens, direct fluorescent antibody test, urine antigen test, and serum antibody assay. The availability, cost, and sensitivity and specificity of the tests should be considered when infection with Legionella is suspected. Table 3 details specific test characteristics. The cost and availability of the tests may depend on the institution in which the testing is performed. Individual practitioners should be aware of the availability and costs of the tests and the time required for test results at institutions where they practice.
The urine antigen test is highly specific, provides rapid results, and is particularly useful when sputum samples are not readily available. Although this test detects only L pneumophila serology group 1, and not other forms of the bacterium,12 this serology group accounts for 80% of the cases of legionnaires disease.12 Culture of sputum and direct fluorescent antibody tests may be difficult to use because of the lack of sputum, the need for a special agar, and special preparation of the medium. On the other hand, the specificity of the sputum test is remarkably high. The test for serum antibodies to Legionella has a high specificity, but the lowest sensitivity, in part because a 4-fold increase in antibody levels is necessary for detection of the antibodies.13 Additionally, an antibody response may not be detectable until after 4 to 12 weeks of infection.13
Treatment
The goal of treatment in legionnaires disease is rapid detection and appropriate antibiotic therapy. Mortality due to the infection increases to 5% to 10% when treatment is delayed.14 The choice of antibiotic depends mostly on the patient’s comorbid conditions, the volume required of the intravenous antibiotic, the ease of eventual oral intake of antibiotics, drug-drug interactions, superiority of antibiotic actions, and cost. All of these factors should be considered at the time of prescribing. Table 4 summarizes suitable and effective antibiotic choices in the treatment of legionnaires disease. Intravenous antibiotics should be administered for the initial 3 to 5 days until clinical improvement occurs. Then a switch to oral antibiotics can be made for a total of a 10- to 14-day course of treatment.
Patients with legionnaires disease can be effectively treated, and a better outcome may occur if the disease is detected early. All practitioners involved in the care of these patients should be knowledgeable about the prevalence, pathophysiology, evaluation, and treatment of the disease.
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REFERENCES
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Case Study
Discussion
