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Legionnaires Disease Treatment & Management

  • Author: Burke A Cunha, MD; Chief Editor: Michael Stuart Bronze, MD  more...
Updated: Mar 30, 2016

Approach Considerations

A delay in treatment significantly increases the risk of mortality in Legionnaires disease (LD). Therefore, include empiric anti-Legionella therapy in the regimen for severe community-acquired pneumonia (CAP) and in specific cases of nosocomial pneumonia.

Although Legionella pneumonia can present as a mild illness, most patients require hospitalization with parenteral antibiotics. Most healthy hosts exhibit clinical response to treatment within 3-5 days.


Prehospital and Emergency Department Care

Prehospital care

Oxygen therapy is the mainstay of prehospital therapy in LD. Intravenous (IV) access and fluid therapy may be indicated for dehydration or septic shock. Restraints may be required for patients with altered mental status. Seizure precautions may be indicated.

Differentiating LD with multiple rigors and altered mental status from a seizure disorder may be possible only through a clinical examination.

Emergency department care

Patient management includes the following:

  • Control the airway as indicated clinically; support ventilation and oxygenation
  • Rehydrate the patient as indicated, especially in shock or diarrheal disease
  • Antipyretics may be used as indicated
  • Cardiac monitoring may be required if chest pain, hypotension, bradycardia, or other indicators are present
  • Obtain laboratory specimens (respiratory culture and urine antigen testing), chest radiographs, computed tomography (CT) scans, and cerebrospinal fluid (CSF), as indicated
  • Begin empiric antibiotic therapy

Also see the Legionella home page from the Centers for Disease Control and Prevention (CDC), as well as the Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community-Acquired Pneumonia in Adults.[12]


Inpatient Care

Patients with mild to moderate pneumonia are admitted to the hospital for parenteral antibiotics and supportive measures. Patients deemed to have a severe pneumonia may require admission to the intensive care unit (ICU) for closer monitoring. Quickly initiate empiric antibiotic treatment and obtain a diagnostic workup.

Close follow-up with a pulmonologist or infectious disease specialist is recommended following discharge.


Antibiotic Therapy

In milder cases, patients can be treated in an outpatient setting with oral antibiotics. For patients who are hospitalized and treated with IV antibiotics, start oral antibiotics while in the hospital and observe the patients for continued response. Continue oral antibiotics on an outpatient basis for 14-21 days, depending on the severity of the presenting illness. Patients should receive close follow-up care to ensure complete resolution of their respiratory symptoms.

Patients should complete the full course of antibiotics, whether the treatment is initiated in the outpatient setting or in the hospital.

Historically, erythromycin, one of the original macrolide antibiotics, was used for L pneumophila infection. Currently, however, other antibiotics, including doxycycline, tigecycline, azithromycin, and a respiratory quinolone, are preferred, because they are more active against LD activity and have superior pharmacokinetic properties (eg, better bioavailability, better penetration into macrophages, longer half-life).

For severe disease, a fluoroquinolone is recommended. With doxycycline or fluoroquinolones, rifampin does not need to be added in severely ill patients.



Consultation with a pulmonologist or infectious disease specialist is strongly recommended in cases of LD. Because of the protean presentation of this disease, however, consultations with other specialists, including the following, may be required at one time or another:

  • General internist
  • Critical care specialist
  • Cardiologist
  • Gastroenterologist
  • Neurologist
  • Nephrologist
  • Oncologist
  • General surgeon

Deterrence and Prevention

Prevention and control of nosocomial legionellosis

Legionellae should be sought in hospitalized patients with an increased risk for infection and subsequent death. If 1 definite case or 2 possible cases of nosocomial LD occur among in patients, initiate an investigation for a hospital source.

Legionellae transmission can also be discouraged through the routine maintenance of cooling towers and the use of only sterile water for filling and rinsing nebulization devices. Improved design and maintenance of cooling towers and plumbing systems can also help.


Superheating water to 70-80°C, with flushing of distal sites, may help to prevent water contamination.

Copper-silver ionization units—which produce metallic ions that disrupt the bacterial cell wall, thus resulting in lysis and cell death—are very effective at eradicating legionellae; they provide sustained protection.

Ultraviolet light kills legionellae by damaging cellular deoxyribonucleic acid (DNA). This modality is effective when disinfecting localized areas, but because it provides no sustained protection, adjunctive treatments must be used.

Hyperchlorination of water is no longer recommended, because legionellae are fairly chlorine resistant, and chlorine decomposes at the higher temperatures found in the hot water systems it is used to treat.

Contributor Information and Disclosures

Burke A Cunha, MD Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital

Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

Michael Stuart Bronze, MD David Ross Boyd Professor and Chairman, Department of Medicine, Stewart G Wolf Endowed Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center; Master of the American College of Physicians; Fellow, Infectious Diseases Society of America

Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American Medical Association, Oklahoma State Medical Association, Southern Society for Clinical Investigation, Association of Professors of Medicine, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Additional Contributors

Frank C Smeeks, III, MD Specialty Medical Director of Emergency Medicine, Applied Medico Legal Solutions

Frank C Smeeks, III, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, American Association for Physician Leadership, American Medical Association, North Carolina Medical Society

Disclosure: Nothing to disclose.


Joseph F John Jr, MD, FACP, FIDSA, FSHEA Clinical Professor of Medicine, Molecular Genetics and Microbiology, Medical University of South Carolina College of Medicine; Associate Chief of Staff for Education, Ralph H Johnson Veterans Affairs Medical Center

Disclosure: Nothing to disclose.

Eric M Kardon, MD, FACEP Attending Emergency Physician, Georgia Emergency Medicine Specialists; Physician, Division of Emergency Medicine, Athens Regional Medical Center

Eric M Kardon, MD, FACEP is a member of the following medical societies: American College of Emergency Physicians

Disclosure: Nothing to disclose.

Fred A Lopez, MD Associate Professor and Vice Chair, Department of Medicine, Assistant Dean for Student Affairs, Louisiana State University School of Medicine

Fred A Lopez, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians-American Society of Internal Medicine, Infectious Diseases Society of America, and Louisiana State Medical Society

Disclosure: Nothing to disclose.

Scott Savage, DO Associate Clinical Faculty, Department of Emergency Medicine, Wright State University, Boonshoft School of Medicine

Disclosure: Nothing to disclose.

Lynn E Sullivan, MD Assistant Professor of Medicine, Yale University School of Medicine

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Jeter (Jay) Pritchard Taylor III, MD Compliance Officer, Attending Physician, Emergency Medicine Residency, Department of Emergency Medicine, Palmetto Health Richland, University of South Carolina School of Medicine; Medical Director, Department of Emergency Medicine, Palmetto Health Baptist

Jeter (Jay) Pritchard Taylor III, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

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This electron micrograph depicts an amoeba, Hartmannella vermiformis (orange), as it entraps a Legionella pneumophila bacterium (green) with an extended pseudopod. After it is ingested, the bacterium can survive as a symbiont within what then becomes its protozoan host. The amoeba then becomes a so-called "Trojan horse," since, by harboring the pathogenic bacterium, the amoeba can afford it protection. In fact, in times of adverse environmental conditions, the amoeba can metamorphose into a cystic stage, enabling it, and its symbiotic resident, to withstand the environmental stress. Image courtesy of the Centers for Disease Control and Prevention and Dr. Barry S Fields.
Table 1. Legionnaires Disease: Six Clinical Predictors and Diagnostic Eliminators in Adults Admitted with Pneumonia a
Diagnostic Predictors Diagnostic Eliminators
Clinical Predictors
  • Fever (>102°F)
Clinical Eliminators
  • Sore throat
  • Severe myalgias
Laboratory Predictors b
  • Highly elevated ESR (>90 mm/h) or CRP (>180 mg/L)
  • Highly elevated ferritin levels (>2 X normal)
  • Hypophosphatemia (on admission/early)
  • Highly elevated CPK (>2 X normal)
  • Microscopic hematuria (on admission)
Laboratory Eliminators
  • Leukopenia
  • Thrombocytopenia
  • Negative chest radiographic findings (no infiltrates)
Legionnaire disease very likely if >3 predictors present Legionnaires disease very unlikely if <3 predictors or >3 diagnostic eliminators present
Abbreviations: CPK = creatinine phosphokinase test; CRP = C-reactive protein; ESR = erythrosedimentation rate.

a Pulmonary symptoms: shortness of breath, cough, and so forth with fever and a new focal/segmental infiltrate on chest radiograph.

b Otherwise unexplained. If finding is due to an existing disorder, it should not be used as a clinical predictor.

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