Legionella Infection Treatment & Management

Updated: Jun 05, 2023
  • Author: Mobeen H Rathore, MD, CPE, FAAP, FIDSA; Chief Editor: Russell W Steele, MD  more...
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Approach Considerations

Inpatient care

Most patients with Legionnaires disease (LD) require initial hospitalization for intravenous antibiotics.

  • Closely monitor patients for signs of shock and/or respiratory or multiorgan failure and the need for ICU care.

  • Patients who begin to steadily improve can be switched to oral antibiotics.

  • Continue to monitor patients in the hospital for at least 1 day after switching to oral antimicrobial therapy because relapse is possible.

Patients with Pontiac fever do not require hospitalization.

Surgical care

Surgical drainage of pulmonary or extrapulmonary disease may be necessary.

Outpatient care

Outpatient treatment with oral antibiotics may be considered for selected patients with mild disease if they can be closely monitored for signs of deterioration.

Continue outpatient treatment after the patient is discharged from the hospital until antibiotic therapy is completed and symptoms resolve.


Medical Care

For Legionnaires disease (LD), a high level of suspicion and prompt initiation of adequate antimicrobial therapy are critical to improve clinical outcomes. [37] In contrast, for Pontiac fever, treatment is symptomatic, and no antimicrobial therapy is recommended.

Therapy effective in patients with legionellosis should be considered for initial empirical treatment for severe community-acquired pneumonia (CAP) and for specific patients with nosocomial pneumonia. Support therapy in patients with shock and respiratory failure is administered as needed.

  • Situations suggesting Legionella disease

    • Gram stains of respiratory samples revealing many polymorphonuclear leukocytes with few or no organisms

    • Hyponatremia

    • Pneumonia with prominent extrapulmonary manifestations (eg, diarrhea, confusion, other neurologic symptoms)

    • Failure to respond to administration of beta-lactams, aminoglycoside antibiotics, or both

  • Antimicrobial therapy for Legionella disease

    • Specific therapy includes antibiotics capable of achieving high intracellular concentrations (eg, macrolides, quinolones, ketolides, tetracyclines, rifampin). The reported rank order of in vitro and intracellular activity against L pneumophila is quinolones, then ketolides, and then macrolides [38] . Beta-lactams and aminoglycosides have activity against Legionella species in vitro but are not clinically effective.

    • No prospective randomized studies have been performed regarding antibiotic effectiveness in patients with Legionella disease. Recommendations are based on retrospective reviews and experimental (laboratory and animal) studies.

    • Azithromycin is the drug of choice for children with suspected or confirmed Legionella disease. [1] With rare exceptions, the initial course should be intravenously administered. After a good clinical response is observed, it can be switched to the oral route. In patients with severe disease or who appear to be unresponsive to monotherapy, the addition of rifampin is recommended.

    • Certain fluoroquinolones (eg, levofloxacin, moxifloxacin) are effective and are recommended for adults with severe disease. [39] Because macrolides may interfere with drugs metabolized by cytochrome P450 (CYP) 3A4 isoenzyme (eg, cyclosporine), the quinolones mentioned above are suitable alternatives to treat Legionnaires disease in patients taking cyclosporine or other CYP3A4 substrates. An older fluoroquinolone, ciprofloxacin, does inhibit CYP3A4. Although the US Food and Drug Administration (FDA) has not approved fluoroquinolones for persons younger than 18 years (because of concerns about arthropathy in studies of juvenile animals), they have been successfully used to treat children with Legionnaires disease [3, 40, 13] and may be used in children in special circumstances.

    • Other alternatives include doxycycline or trimethoprim (TMP) and sulfamethoxazole (SMZ).

    • The recommended duration of therapy is 5-10 days if azithromycin is used. If other drugs are used, the duration should be 2-3 weeks. For patients with severe disease or immunocompromise, prolonged courses may be required.



Consultations may include the following:

  • Infectious disease specialist

  • Critical care specialist

  • Pulmonologist

  • Health-department officials: Confirmed cases of Legionnaires disease should be reported to local health-department officials. Legionellosis is a notifiable disease in the United States.



Patients with Legionnaires disease do not require contact or respiratory isolation (person-to-person transmission has never been demonstrated). Standard precautions are recommended. [1]

For water births, the colonization of tap water with Legionella can be reduced by installation of a filter system into the supply hose of the birthing tub.

Strategies the Centers for Disease Control and Prevention (CDC) recommend to prevent healthcare-associated (HCA) Legionnaires disease include the following:

  • Maintain a high index of suspicion for the diagnosis of HCA Legionnaires disease, and perform appropriate laboratory tests for Legionnaires disease.

  • Facilities with transplantation programs should consider routine Legionella cultures of water samples from the potable water systems as part of the facilities comprehensive program to prevent and control HCA Legionnaires disease.

  • Maintain potable water at the outlet at temperatures not suitable for the growth of Legionella species.

  • Cooling towers should receive routine maintenance, and only sterile water should be used to fill and rinse respiratory therapy devices.

  • Initiate an investigation for the source of Legionella organisms when one case of Legionnaires disease is identified in an inpatient transplant recipient or when 2 cases occurring within 6 months of each other are identified in transplant recipients who visited an outpatient unit during the 2-10 months before the onset of illness.

  • If the water system is implicated, decontaminate the system by superheating water to 71-77°C, and maintain until distal sites are flushed. If thermal shock is not possible, use shock chlorination as an alternative. [41]

Some experts have recommended to culture the tap water of pediatric hospitals, especially to sample the higher risk areas (eg, NICU, PICU, transplant units) for Legionella. Children with hospital-acquired pneumonia in hospitals with positive surveillance cultures should undergo Legionella testing. [42]

Additionally, it has been recommended that transplant recipients boil their water, cool it, and store it for drinking. [43]