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Symptoms & Signs

• History
  • Most typical signs/symptoms
    • Fever
    • Cough (nonproductive or productive of purulent sputum)
    • Pleuritic chest pain
    • Chills and/or rigors
    • Dyspnea
  • Frequent signs/symptoms
    • Headache
    • Nausea
    • Vomiting
    • Diarrhea
    • Fatigue
    • Arthralgia/myalgia
    • Falls and new-onset or worsening confusion (in elderly patients)
• Physical findings
  • Fever
  • Tachypnea
    • In two studies, patients with a respiratory rate of > 25/min had a pneumonia likelihood ratio of 1.5–3.4.
  • Tachycardia
    • Patients with a heart rate of ≥100/min, a temperature of ≥ 37.8°C, and a respiratory rate of ≥20/min were 5 times more likely to have pneumonia than patients without these findings in one study.
  • Chest examination
    • Dullness to percussion
    • Increased tactile and vocal fremitus
    • Egophony
    • Whispering pectoriloquy
    • Crackles
    • Pleural friction rub

Differential Diagnosis

• Infections
  • Lung abscess
  • Bronchitis
• Noninfectious illnesses
  
  • Pulmonary embolism
  • Pulmonary hemorrhage
  • Pulmonary edema
  • Pulmonary fibrosis/scarring
  • Inflammatory disorders
    • Sarcoidosis
    • Wegener’s granulomatosis
    • Other rheumatologic/vasculitic diseases
  • Lung cancer
  • Hypersensitivity pneumonitis
  • Bronchiolitis obliterans organizing pneumonia
  • Others
    

Diagnostic Approach

• Assess pneumonia severity.
  • Pay attention to vital signs, including oxygen saturation.
  • Always count the respiratory rate yourself for 1 min.
    • The single most useful clinical sign of severity is a respiratory rate of > 30/min in a person without underlying lung disease.
  • Ensure adequate oxygenation and support of circulation during the evaluation.
• Consider possible etiologies.
  
  • Carefully collect information on:
    • Travel
    • Occupational and other exposures
    • Underlying illnesses
    • Prior infections
  • Never forget tuberculosis and Pneumocystis infection as possible etiologies.
  • Consider pulmonary embolus in all patients with pleuritic chest pain.
• Perform etiologic workup.
  • Chest x-ray
  • Sputum stains and cultures
  • Blood cultures, if bacteremia is likely
  • Urine antigen tests for S. pneumoniae and Legionella pneumophila type 1 can be helpful.
  • Serology can be helpful in identifying certain pathogens.

Laboratory Tests

Nonspecific studies

• Assessment of the severity of pneumonia and coexisting disease
  • Arterial blood gas
  • Complete blood count
  • Serum electrolyte and glucose measurements
  • Blood urea nitrogen (BUN) and creatinine measurements
    

Sputum stains and culture

• Gram’s stain
  
  • Useful in screening a sputum sample for suitability for culture and in making a presumptive etiologic diagnosis
    • A sputum sample with > 25 white blood cells (WBCs) and < 10 squamous epithelial cells per low-power field is suitable for culture.
    • Significant interobserver variability exists in the interpretation of gram-stained sputum smears.
  • The presence of any gram-positive diplococci has a sensitivity of 100% but a specificity of 0 for a diagnosis of pneumococcal infection.
    • The presence of > 10 gram-positive diplococci per oil-immersion field has a sensitivity of 55% and a specificity of 85% for this diagnosis.
• Other sputum stains that may be helpful in some patients
  
  • Stains for
    • Acid-fast bacilli
    • Pneumocystis
    • Fungi
    • Cytology
  • Rapid antigen testing for viral pathogens (e.g., influenza)
• Culture
  • Results should always be correlated with those of Gram staining.
    • If an organism is isolated from sputum and its morphologic correlate is not seen on Gram staining, the isolate may be colonizing the upper airway.
  • Certain microorganisms, if isolated from sputum, should always be considered pathogens. These include:
    • M. tuberculosis
    • Legionella spp.
    • Blastomyces dermatitidis
    • Histoplasma capsulatum
    • Coccidioides immitis
  • Only about one-third of elderly patients admitted with CAP produce sputum suitable for culture.
    • One-third of these specimens fail to yield a pathogen.

Blood culture

• Blood should be obtained for culture from patients to be treated on an ambulatory basis if they have been receiving antibiotic therapy and have presented because of any of the following:
  • Hyperthermia (body temperature > 38.5°C)
  • Hypothermia (body temperature < 36°C)
  • Homelessness
  • Alcohol abuse
• All patients admitted to the hospital for CAP should have 2 sets of blood cultures done before initiation of antibiotic therapy (positivity rate: 6–20%).
• The most common isolates, in descending order, are S. pneumoniae (~60%), S. aureus , and Escherichia coli .

Detection of antigens of pulmonary pathogens in urine

• L. pneumophila (see Legionellosis)
  
  • Serogroup 1 antigen can be detected in the urine of patients with Legionnaires’ disease by enzyme-linked immunosorbent assay (ELISA).
    • Sensitivity: 69–72% on average, 88–100% in severe disease, 40–53% in mild disease
    • Sensitivity: low in nosocomial Legionnaires’ disease
    • The results may be negative early in the illness, and antigen excretion can be prolonged.
  • This test should be used for patients in whom Legionnaires’ disease is strongly suspected, including those with rapidly progressive pneumonia.
  • The urine antigen test is now the most frequently used diagnostic method for Legionnaires’ disease.
  • Infection with Legionella spp. other than L. pneumophila serogroup 1 gives a negative test result.
• S. pneumoniae
  
  • Urinary antigen detection by ELISA has a sensitivity of 80% and a specificity of 97–100% in patients with bacteremic pneumococcal pneumonia.
    • The antigen may be detected for up to 1 month after the onset of pneumonia, and the results can be available in 15 min.
    • In children, nasopharyngeal carriage of S. pneumoniae can result in a positive urinary antigen test.

Serology

• Detection of IgM antibody or demonstration of a 4-fold rise in titer of antibody to a particular agent between acute- and convalescent-phase serum samples generally is considered good evidence that this agent is the cause of CAP.
• The following etiologic agents often are diagnosed serologically:
  • M. pneumoniae
  • C. pneumoniae
  • Chlamydia psittaci
  • Legionella spp.
  • Coxiella burnetii
  • Adenovirus
  • Parainfluenza viruses
  • Influenza virus A
• The serologic tests include complement fixation, indirect immunofluorescence, and ELISA.
• Separate IgM and IgG antibody detection tests can be performed with the latter 2 assays.
• One difficulty in relying on serology is that a polyclonal antibody response to one agent may result in a 4-fold rise in antibody titer to others.
  • Thus, results may be nonspecific.
• Serologic testing is not recommended for routine use.
  • If agents such as C. burnetii are suspected, serologic testing is necessary.
  • Serology is a useful part of the workup of outbreaks of pneumonia associated with negative blood and sputum cultures.

Polymerase chain reaction (PCR)

• Amplification of the DNA or RNA of microorganisms that are not part of the pharyngeal flora (from microbial cells collected by throat swab) has been used to infer that the implicated microorganism is the cause of pneumonia.
• A multiplex PCR allows detection of DNA of Legionella spp., M. pneumoniae, and C. pneumoniae.
• This test is expensive and is not routinely available.

Imaging

• Chest x-ray
  • Diagnostic test of choice for pneumonia
  • May show lobar consolidation, interstitial infiltrates, cavitation, associated pleural fluid, etc.
  • Occasionally, an etiologic diagnosis is suggested by chest radiography findings.
    
    • A cavitating upper-lobe lesion raises the likelihood of tuberculosis.
    • Pneumatoceles suggest S. aureus pneumonia.
    • An air-fluid level suggests a pulmonary abscess, which often is polymicrobial.
    • In the immunocompromised host, a crescent (meniscus) sign suggests aspergillosis.
  • In most instances, no etiologic inference can be made from radiographic abnormalities, despite the traditional teaching that a lobar vs. interstitial appearance may be more suggestive of "typical" bacterial vs. "atypical" bacterial or nonbacterial etiologies.
  • If pneumonia is strongly suspected on clinical grounds and no opacity is seen on the initial chest radiograph, it is useful to repeat the radiograph in 24–48 hours or to perform CT.
    • Correction of dehydration may lead to development of chest film infiltrates.
  • Opacity visible on the chest radiograph may not be due to pneumonia; many other disease processes can result in opacities (see Differential Diagnosis).
• High-resolution CT
  • Occasionally detects pulmonary opacities in patients with symptoms and signs suggestive of pneumonia and negative chest x-ray
  • More likely than chest radiography to show bilateral involvement, pleural fluid/empyema, adenopathy, etc.
    

Diagnostic Procedures

• Thoracentesis
  • If a pleural effusion of > 1 cm is detected on lateral decubitus chest x-ray, the fluid should be sampled for studies including Gram’s stain, culture, cell counts, and measurements of protein, lactate dehydrogenase (LDH), glucose, and pH.
  • See Pleuritis.
• Bronchoscopy/bronchoalveolar lavage/lung biopsy:
  • May be required to obtain material for further studies when the diagnosis defies other diagnostic efforts and the patient does not improve despite empirical therapy
    

The Harrison's Practice Preview allows you to view 5 FREE complete topics or conduct a search that delivers abstracts for more than 450 medical topics. For full access, please subscribe today!