Clinical Geriatrics

Legionella pneumonia is an infrequent, often community-acquired pneumonia (CAP) that may present occasionally to healthcare providers. The sporadic nature of this type of pneumonia may lead to the misdiagnosis as a simple pneumonia, especially in otherwise healthy individuals. Legionella pneumonia is also unique in that it is not transmitted person to person; its mode of transmission appears to be through contaminated water or inhalation of bacteria.

Pneumonia has been divided into two categories: CAP and healthcare-associated pneumonia (HCAP), the latter of which includes hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP). Patients with these diagnoses frequently present either to the Emergency Department for hospital admission or as visitors to a primary medical practitioner seeking outpatient treatment. Additional considerations are the decisions of whether or not to admit a patient with pneumonia to an inpatient facility, and when to do so.

To accurately diagnose and treat pneumonia, practitioners need to be aware of local susceptibility and resistance patterns of common pathogens. Current hospital-based antibiograms are usually available to local practitioners for the benefit of selecting the correct antibiotic.¹

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The Infectious Diseases Society of America/American Thoracic Society guidelines define CAP, HCAP, HAP, and VAP diagnoses as follows²:

Community-acquired pneumonia:
• Patients with pneumonia who do not meet HCAP, HAP, or VAP criteria

Healthcare-associated pneumonia:
• Patients who are hospitalized for more than two days in an acute care facility within 90 days of infection, residing in a nursing home, or residing in a long-term care facility
• Patients who are attending a hospital or hemodialysis clinic
• Patients who are receiving intravenous antibiotic therapy or immunosuppressive therapy, or wound care within 30 days of infection

Hospital-acquired pneumonia:
• Patients with pneumonia occurring 48 hours or more after hospital admission

Ventilator-associated pneumonia:
• Patients with pneumonia occurring more than 48-72 hours post-intubation²

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Legionella pneumophila (Legionella) , often known as Legionnaires’ disease, is an atypical bacterial infection responsible for both CAP and HCAP in the United States. Legionella pneumophila is the most common strain for the more than 40 different strains of legionellosis, with serogroup 1 being the most likely.³ Forgie et al⁴ noted that a more accurate number is 48 species of Legionella, with approximately 24 species causing pneumonia. A German study of 2503 adult patients with CAP noted that Legionella was diagnosed in 94 patients (3.8%). Vonbaum and colleagues suggested that Legionella is the most common pathogen to cause CAP in both ambulatory and inpatient hospitalizations.⁵

Cases of Legionella may occur as part of an outbreak or in isolated instances. Pontiac fever, a milder illness caused by the Legionella bacteria, is rarely fatal, and patients are infrequently hospitalized due to its self-limiting nature. However, where there are suspected cases of Pontiac fever, there are likely cases of Legionella pneumophila present. Careful reporting of such suspicions to the local Department of Health can avoid an epidemic of either Pontiac fever or Legionella pneumophila. Legionella does not have seasonal variation; therefore, there is not an increase in outbreaks during the winter and spring. The frequency of Legionella appears to increase during the summer and early fall months.