Chapter 5-8: Evidence-Based Diagnosis

Initial evaluation

1. Should include a chest radiograph, blood and sputum cultures, sputum Gram stain, and WBC

2. Urinary pneumococcal and Legionella pneumophila serogroup 1 Ag testing is performed routinely and often helpful.

Airborne precautions should be followed in all HIV-infected patients with pneumonia.

1. They should be placed in a negative-pressure isolation room.

2. 3 sputum acid-fast stains should be done to rule out pulmonary TB.

Toxic appearance is uncommon but suggests bacterial pneumonia over PJP or pulmonary TB (sensitivity, 10.6%; specificity, 97.8%; LR+, 4.8)

Pneumococcal pneumonia

1. Common symptoms include cough (93%), subjective fever (90%), pleural pain (52–91%), and chills (74%); 51% of patients have hemoptysis and 63% have temperature > 38°C.

2. The median duration of symptoms is 4 days.

3. Sputum Gram stain is 58% sensitive and more frequently positive if collected within 24 hours of antibiotics.

4. Sputum culture is 56% sensitive: the real pathogen is more often isolated if sputum culture is performed before starting antibiotics. When sputum culture is delayed > 24 hours after starting antibiotic, respiratory colonizers are more often isolated; for example, a respiratory sample obtained from a person with severe pneumonia caused by S pneumoniae who has been intubated in the ICU for 48 hours may grow P aeruginosa that colonizes the ventilator tubing without causing pneumonia.

5. Blood cultures are positive in 31–95%.

6. Pneumococcal urinary Ag: ≈79% sensitive and 94% specific (LR+, 13; LR–, 0.2). The test may be also be positive due to colonization or upper respiratory infections with S pneumoniae.

Legionella pneumonia

1. One study reported that certain findings were more common in patients with Legionella pneumonia than S pneumoniae, including extra-respiratory symptoms (57% vs 24%), hyponatremia (57% vs 13%), and elevated creatine phosphokinase (57% vs 17%).

2. Respiratory failure is more common with Legionella than S pneumoniae (33% vs 2%).

M pneumoniae is usually diagnosed by IgM ELISA, 4-fold change in IgG, or the presence of cold agglutination.

Chest radiograph

1. Standard imaging includes posteroanterior plus lateral chest radiograph.

2. Typically demonstrates lobar or multifocal consolidation.

3. Lobar consolidation is not always seen but strongly suggests bacterial pneumonia over PJP or pulmonary TB (sensitivity, 54%; specificity, 90%; LR+, 5.6; LR–, 0.51).

4. Lobar infiltrates in patients with fever for < 1 week strongly suggests bacterial pneumonia (sensitivity, 48%; specificity, 94%; LR+, 8.0; LR–, 0.55).

5. Chest radiographic patterns did not distinguish S pneumoniae from P aeruginosa or Legionella infection.

6. One report found that 82% of HIV-infected persons with pulmonary complaints had abnormalities, including pleural effusions, cavities and abscess, on high-resolution CT scans that were not detected on chest radiograph.

Bronchoscopy

1. Indicated in patients who do not respond to therapy or when concomitant infection is likely.

2. Sensitivity of bronchoalveolar lavage for bacterial pneumonia: 70% (if performed early)