Legionella Infection Clinical Presentation

Updated: Jun 05, 2023
  • Author: Mobeen H Rathore, MD, CPE, FAAP, FIDSA; Chief Editor: Russell W Steele, MD  more...
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Pneumonia is the predominant clinical manifestation of Legionnaires disease (LD). After an incubation period of 2-10 days, patients typically develop the following nonspecific symptoms:

  • Fever

  • Weakness

  • Fatigue

  • Malaise

  • Myalgia

  • Chills

Respiratory symptoms may not be present initially but develop as the disease progresses. Almost all patients develop a cough, which is initially dry and nonproductive, but may become productive, with purulent sputum and, (in rare cases) hemoptysis. Patients may experience chest pain.

Neurologic and GI symptoms are usually prominent. Neurologic complaints may include the following:

  • Headache

  • Lethargy

  • Confusion

  • Cerebellar ataxia

  • Agitation

  • Stupor

Common GI symptoms include diarrhea (watery and nonbloody), nausea, vomiting, and abdominal pain. [28]

In neonates, Legionnaires disease can manifest as septicemia and/or pneumonia with a fulminant course, often diagnosed at autopsy.

Extrapulmonary legionellosis is rare; the most common site of extrapulmonary infection in adults is the heart. In children, extrapulmonary sites may include the liver, spleen, brain, and lymph nodes. [29] Manifestations of extrapulmonary legionellosis may include the following:

Pontiac fever is an influenzalike illness, typically with an abrupt onset. The incubation period is 24-48 hours. Prominent symptoms include fever, malaise, myalgia, cough, and headache. Pontiac fever tends to occur in outbreaks, and the infection rate is greater than 90%. The disease is self-limiting, persisting for approximately 1 week.


Physical Examination

The severity of illness at presentation varies from mild nonspecific findings to profound respiratory and/or multiorgan failure.

  • Fever is typically present (98%). Temperatures exceeding 40°C occur in 20-60% of patients. The occurrence of bradycardia relative to fever has been overemphasized, but it may occur in patients with advanced pneumonia. [28]

  • Hypotension has been reported in 17% of patients with community-acquired pneumonia (CAP).

  • Lung examination reveals rales and signs of consolidation late in the disease course.

  • In patients with extrapulmonary legionellosis, physical findings relate to the involved organs.

  • Manifestations in children who are immunocompromised appear similar to manifestations in adults. However, in neonates, signs of sepsis with multisystemic involvement appear to be more prominent. Progression to respiratory failure is very rapid, and the disease is likely to be fatal. [30]