Legionella Infection

Clinical Manifestations and Diagnosis

Legionnaire's disease (pneumonia)

• clinical features
  • similar to other forms of pneumonia - fever, cough, SOB -  respiratory symptoms preceded often by fever and fatigue
  • 2-10 days post exposure to contaminated water or soil
  • radiographic findings are nonspecific - most commonly patchy unilobar infiltrates that progress to consolidations
  • associated with:
    • GI symptoms (nausea, vomiting, diarrhea)
    • hyponatremia
    • liver enzyme elevations
    • CRP > 100
    • failure to respond to beta-lactam monotherapy
  • ranges in severity from mild to severe
  • Clinical features of Legionnaires' disease do not appear to vary with the infecting species or serotypes
• diagnosis
  • suspect Legionella with:
    • any pneumonia
    • known outbreaks - water contamination in large facilities
    • contaminated water sources such as hot tubs, fountains; exposures to soil or potting mix
  • risk factors
    • older age, smoking, chronic disease
  • no specific guidelines to test, but:
    • All patients with moderate to severe CAP or patients with CAP who require hospitalization
    • Any patient with CAP or nosocomial pneumonia who has a known or possible exposure to Legionella (eg, during an outbreak)
    • Immunocompromised patients (who are at higher risk for Legionella infection and severe disease)
  • approach to testing
    • When testing for Legionella in patients with pneumonia, we prefer to use PCR on a lower respiratory tract sample (eg, sputum or bronchoalveolar lavage specimen) because PCR has high diagnostic accuracy and detects all Legionella species and serogroups.
    • If PCR is not available or if sputum cannot be obtained, urine antigen testing is an acceptable alternative, especially in regions such as the United States where the prevalence of L. pneumophila serogroup 1 is high. The main advantages of the urinary antigen test are its rapid turnaround time and high specificity.
      • sensitivity of urine antigen tests ranges from approximately 70 to 80 percent and the specificity approaches 100 percent in patients with Legionnaires' disease caused by L. pneumophila serotype 1
      • L. pneumophila serotype 1 causes over 80 percent of reported cases of Legionnaires' disease in most regions of the world

Pontiac fever (febrile illness)

• acute, self-limited febrile illness, which can follow exposure to several Legionella species
• Symptoms are nonspecific and include fever, headache, chills, myalgias, nausea, vomiting, and diarrhea
• Symptom onset occurs approximately 4 to 60 hours after exposure (median 36 hours)
• The duration of illness ranges from one to nine days (median four days) and typically resolves without specific therapy
• In contrast with Legionnaires' disease (Legionella pneumonia), signs and symptoms of lower respiratory tract infection are absent
• Because Pontiac fever is typically self-limited, testing is usually not performed unless part of an epidemiologic investigation

Extrapulmonary infection

Causes all sorts of infections: SSTI, joints, bones, myocardium and pericardium, cardiac valves, kidneys, etc...

Treatment

Legionella pneumonia

• empiric treatment
  • For most patients with CAP, the etiology is not known at the time of diagnosis, and empiric treatment is appropriate
  • generally include an antibiotic that targets Legionella (eg, a fluoroquinolone or macrolide) when selecting an empiric antibiotic regimen for most patients with CAP
  • generally avoid tetracyclines (doxycycline) for legionellosis
• directed treatment
  • Levofloxacin and azithromycin are the preferred directed agents.
    • cohort studies have not found differences in mortality when comparing levofloxacin with azithromycin
    • Higher doses of levofloxacin (ie, 750 mg daily) may lead to faster symptom resolution than lower doses (500 mg daily); therefore choose higher doses when using this drug
    • Combination therapy using both a fluoroquinolone and a macrolide does not appear to improve outcomes
  • Duration of therapy
    • optimal duration of therapy for the treatment of Legionnaires' disease has not been determined
    • treat for a minimum of five days and do not stop therapy until the patient is clinically stable and afebrile for at least 48 hours
• response to treatment
  • Most patients with Legionnaires' disease respond promptly to treatment, defervescing in approximately two to five days. Resolution of radiographic changes often lag behind clinical improvement, though most clear over a period of two month
  • For patients who are slow to respond to treatment, complications such as lung abscess, empyema, or extrapulmonary infection should be considered. Coinfection with other pathogens is rare

Pontiac fever

Pontiac fever is usually short lived and resolves spontaneously after three to five days. Specific therapy is not needed.

Extrapulmonary disease

Patients with extrapulmonary infections (eg, cellulitis, skin abscesses, septic arthritis, myocarditis, or endocarditis) are most often treated with a fluoroquinolone. Generally, longer courses of therapy are required for patients with extrapulmonary legionellosis than with Legionnaires' disease.

References

1. https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-legionella-infection#H21952827
2. Metlay JP, Waterer GW, Long AC, et al. Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America. Am J Respir Crit Care Med. 2019;200(7):e45-e67. doi:10.1164/rccm.201908-1581ST

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