Legionnaires Disease Clinical Presentation

Updated: Mar 11, 2021
  • Author: Chinelo N Animalu, MD, MPH, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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Legionella pneumophila causes 2 distinct disease entities. Legionnaires disease (LD) is characterized by pneumonia. Pontiac fever is a short-term, milder illness than LD and is not characterized by pneumonia, instead manifesting as fever and myalgias that resolve without treatment. Extra pulmonary legionellosis such as pericarditis, endocarditis and cellulitis although not common, has been reported in both immunocompromised and immunocompetent patients and can occur as isotated cases or in the setting of legionella pneumonia. Usually species other than L pneumophila have been implicated in these cases. [11, 12]

The incubation period in LD ranges from 2-10 days. Patients who develop legionellae infection and who have been hospitalized continuously for 10 or more days before the onset of illness are classified as having definite nosocomial LD. Patients with laboratory-confirmed infection that develops 2-9 days after hospitalization are classified as having possible nosocomial LD. Nosocomial LD occurs in clusters.

Symptoms of LD can occur as follows:

  • Patients often experience a prodrome of 1-2 days of mild headache and myalgias, followed by high fever, and chills

  • Cough is present in 90% of cases; cough usually is nonproductive at first but may become productive as the disease progresses

  • Other pulmonary manifestations include dyspnea, pleuritic chest pain, and hemoptysis, which may be present in as many as one third of cases

  • Gastrointestinal symptoms include nausea, vomiting, diarrhea (watery, not bloody), abdominal pain, and anorexia

  • Neurologic symptoms include headache, lethargy, encephalopathy, altered mental status (the most common neurologic symptom), and rarely, focal symptoms

  • Musculoskeletal symptoms include myalgias

  • Nonpulmonary symptoms are prominent early in the disease


Physical Examination

Manifestations of LD may include the following:

  • Headache

  • Mental status changes

  • Fever greater than 40°C, or 102°F (range, 38.8-40.5°C)

  • Relative bradycardia (excluding patients with pacemakers or arrhythmias or those receiving beta blockers, diltiazem, or verapamil)

  • Myocarditis

  • Prosthetic valve endocarditis

  • Tachypnea

  • Localized rales

  • Blood-streaked sputum

  • Extrapulmonary manifestations

  • Abdominal pain

  • Pancreatitis

  • Acute renal failure

A clinical point score may be helpful in increasing the probability of correctly diagnosing LD and prompting specific/definitive LD testing.

Table 1. Legionnaires Disease: Six Clinical Predictors and Diagnostic Eliminators in Adults Admitted with Pneumonia a (Open Table in a new window)

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.