Pneumonia Caused by Other Pathogens

How to Cite This Chapter: Loeb M, Kuś J, Jankowski M. Pneumonia Caused by Other Pathogens. McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. Accessed July 18, 2024.
Last Updated: February 20, 2016
Last Reviewed: October 22, 2021
Chapter Information


Treatment: see Table 2 in Community-Acquired Pneumonia.

1. Streptococcus pneumoniae: The most common etiologic agent of community-acquired pneumonia (CAP). Sputum cultures are recommended in hospitalized patients, although they may be of limited use. Other methods of confirming the diagnosis include blood cultures (positive results in <25% of cases) and detection of the Streptococcus pneumoniae antigen in urine.

2. Haemophilus influenza and Moraxella catarrhalis may be a cause pneumonia, especially in patients with chronic lung disease.

3. Staphylococcus aureus causes <5% of CAP cases and ~30% of hospital-acquired pneumonia (HAP) cases; the disease usually has a severe course. The diagnosis is confirmed by microscopic examination of sputum samples, sputum cultures, and blood cultures. Patients with methicillin-resistant Staphylococcus aureus (MRSA) infection should be isolated. Infection with Panton-Valentine leukocidin-producing strain (PVL-SA) may lead to the formation of cavities in the lungs (necrotizing pneumonia) and multiple organ failure. Start targeted treatment as soon as results of microbiologic studies are available.

4. Klebsiella pneumoniae and other gram-negative intestinal bacilli (Escherichia coli, Proteus spp): Radiologic features: see Community-Acquired Pneumonia. The diagnosis is confirmed by blood or sputum cultures.

5. Acinetobacter baumannii usually causes HAP that is often severe and associated with leukopenia. Pleural effusions develop in 50% of patients.

6. Anaerobic bacteria are not a frequent cause of CAP and an uncommon cause of ventilator-associated pneumonia (VAP). They are of prime importance in patients with aspiration and may be associated with abscess formation. Detection can be difficult. Microscopic examination of sputum may be helpful.

7. Atypical pathogens:

1) Mycoplasma pneumoniae: The incubation period lasts 2 to 3 weeks. Patients rarely develop leukocytosis or lobar infiltrates. Occasionally hilar lymphadenopathy is observed. Features of hemolytic anemia may be present.

2) Chlamydophila (Chlamydia) pneumoniae typically causes pharyngitis that precedes CAP by ~2 weeks.

3) Legionella pneumophila: Air conditioning systems, air humidifiers, and tap water are potential sources of infection, which may cause headaches and disorientation. Diarrhea may also be observed. The infection may cause elevated serum levels of alanine aminotransferase, aspartate aminotransferase, creatine kinase; hyponatremia; albuminuria; and microscopic hematuria. The diagnosis is confirmed by detection of the L pneumophila antigen in urine.

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