Community-Acquired Pneumonia

Indications for testing

Cough, fever, shortness of breath

Laboratory Testing

CBC – leukocytosis with left shift suggests bacterial etiology
Complete metabolic and electrolyte profile – only used in toxic-appearing patients, patients >55 yeaers
Cultures
- Sputum gram stain and culture
  - Variable yield (sputum may be difficult to obtain)
- Pleural fluid – thoracentesis if >5 cm height on chest X-ray noted
- Bronchoscopic lavage for patients who are severely ill and sputum cannot be obtained
- Blood cultures – should be obtained in patients who will be hospitalized
  - Positive yield <20%
    - Lower yield if antibiotics already started prior to culture
Specific testing (based on clinical presentation and history)
- S. pneumoniae – rapid urine antigen testing
- Legionella spp – rapid urine antigen testing
- Influenza – point-of-care testing or rapid DFA
- M. pneumoniae – need serology testing in most cases
- C. pneumoniae – need serology testing in most cases
Differentiation of lower respiratory tract viral infection versus bacterial infection
- Procalcitonin (PCT)
  - Precursor to calcitonin
  - Final step in synthesis is inhibited by endotoxin and cytokines
  - Elevated in bacterial infections
  - Use in respiratory tract infections to differentiate need to treat with antibiotics
    - Treatment recommendation
      PCT
      Treatment Recommendation
      <0.1 ng/mL
      Antibiotics strongly discouraged
      0.1-0.24 ng/mL
      Antibiotics discouraged
      0.25-0.5 ng/mL
      Antibiotics encouraged
      >0.5 ng/mL
      Antibiotics strongly encouraged

PCT	Treatment Recommendation
<0.1 ng/mL	Antibiotics strongly discouraged
0.1-0.24 ng/mL	Antibiotics discouraged
0.25-0.5 ng/mL	Antibiotics encouraged
>0.5 ng/mL	Antibiotics strongly encouraged

Imaging Studies

Chest x-ray – gold standard for confirmation of pneumonia
- Single or several lobe patterns – bacterial
- Diffuse or interstitial pattern – viral or atypical organism
- Cavitary – more common in gram negative, fungi, acid-fast bacilli
- Miliary – acid-fast bacilli, fungi, atypical pneumonia agents
CT – better tool for small pneumonias; however, the cost, radiation exposure and time negate its use for most patients

Prognosis

Severity scoring stratifies patients based on mortality
- Pneumonia severity index (PSI) (based on study by Patient Outcomes Research Team)
  - PSI uses several clinical variables to calculate a score to predict risk of death
  - Classes I-III have low risk of death and can probably be treated as outpatients
  - Classes IV and V have higher risk of death and should probably be treated as inpatients
  - PSI + PCT
    - In low-risk patients, adds little to prognostication
    - In high-risk patients, PCT <0.1ng/mL suggests better prognosis
- CURB-65 severity score (British Thoracic Society)
  - Clinical prediction rule that has been validated for predicting mortality in community-acquired pneumonia
  - CURB-65 = confusion, urea nitrogen, respiratory rate, blood pressure, ≥65 years of age
- Criteria for severe community-acquired pneumonia (Infectious Disease Society/American Thoracic Society)
  - Major criteria
    - Invasive mechanical ventilation
    - Septic shock with need for vasopressors
  - Minor criteria
    - Respiratory rate >30 breaths/minute
    - Partial pressure of oxygen in arterial blood (PaO₂)/fraction of inspired oxygen (FiO₂) <250
    - New onset of confusion
    - Multilobar infiltrates
    - BUN >20 mg/dL
    - Leukopenia (WBC count <4,000 cells/mm³)
    - Thrombocytopenia (platelets <100,000 cells/mm³)
    - Hypothermia (core temperature <36°C)
    - Hypotension requiring aggressive fluid resuscitation
- Criteria for ICU admission – presence of one major criteria or ≥3 minor criteria

Differential Diagnosis

Lower respiratory tract viral infection
Chronic obstructive disease (COPD) exacerbation
Cancer
- Metastases
- Primary pulmonary tumor
Bronchiolitis obliterans organizing pneumonia
Heart failure
Autoimmune connective tissue disease
Fibrotic disease
Vasculitis

Community-acquired pneumonia (CAP) is pneumonia acquired outside of a hospital or long-term care facility. CAP is a common disease and frequent cause of morbidity and mortality worldwide.

Epidemiology

Incidence – >5 million cases annually in the U.S.
- 12/1,000 in Northern Hemisphere
  - <1 year – 30-50/1,000
  - 15-45 years – 1-5/1,000
  - 60-70 years – 10-20/1,000
  - 71-85 years – 50/1,000
Age – more common in younger and older patients

Risk Factors

Older age
Alcohol abuse
Asthma
Chronic pre-existing disease – heart, lung, liver
Immunocompromised state
Institutionalized patients
Tobacco abuse

Organisms

Organism not identified in more than 35-40% of patients
Viral
- Orthomyxoviridae (influenza A and B)
- Paramyxoviridae
  - Metapneumovirus (hMPV)
  - Parainfluenza virus 1, 2, 3
  - Respiratory syncytial virus (RSV)
- Coronaviriniae (coronavirus)
- Adenoviridae (adenovirus)
- Bunyaviridae (hantavirus)
Bacterial
- Streptococcus pneumoniae
- Haemophilus influenzae
- Atypical organisms
- Staphylococcus aureus
- Moraxella catarrhalis
- Gram-negative bacilli
- Mycobacteria
Fungi
- Blastomycosis
- Coccidioidomycosis
- Histoplasmosis

Clinical Presentation

A patient with normal vital signs and a normal physical exam will have pneumonia <5% of the time
Nonspecific – fever, cough, shortness of breath, chest pain, sputum production
Atypical organisms tend to cause extra-pulmonary disease
- Central nervous system – headache, meningitis, encephalopathy
- Gastrointestinal – diarrhea, hepatitis
- Electrolyte abnormalities
- Renal – renal insufficiency
Complications
- Respiratory failure
- Acute respiratory distress syndrome (ARDS)
- Empyema
- Sepsis

Treatment

Rapid initiation of antibiotics is associated with better outcomes; pathogen-specific therapy advised
- Refer to Infectious Diseases Society of America/American Thoracic Society consensus guidelines

Tests generally appear in the order most useful for common clinical situations

Test name: CBC with Platelet Count & Automated Differential

ARUP #: 0040003

Methodology: Automated Cell Count with Flow Cell Differential

Use:

Leukocytosis with left shift suggests bacterial etiology

Test name: Respiratory Culture (Includes Gram Stain 0060101)

ARUP #: 0060122

Methodology: Standard reference procedures for bacterial stain, aerobic culture, and identification. Sinus swabs or aspirates should be ordered as a Wound Culture (0060132).

Use:

Positive culture aids in diagnosis of CAP

Limitations:

Variable yield because sputum may be hard to obtain

Test name: Respiratory Viruses Rapid Culture

ARUP #: 2001504

Methodology: Cell Culture/Immunofluorescence

Use:

Evaluate for respiratory virus

Respiratory viruses that can be isolated include influenza A & B; parainfluenza types 1, 2, 3; adenovirus; and RSV

Limitations:

Other viruses (such as HSV or CMV) are not routinely detected

Test name: Electrolyte Panel

ARUP #: 0020410

Methodology: Quantitative Ion-Selective Electrode/Enzymatic

Use:

Evaluate for organ dysfunction

Test name: Comprehensive Metabolic Panel

ARUP #: 0020408

Methodology: Refer to individual components

Use:

Evaluate for organ dysfunction

Test name: Influenza Virus A & B DFA with Reflex to Influenza Virus A & B Rapid Culture

ARUP #: 0060284

Methodology: Direct Fluorescent Antibody Stain

Use:

Rapid detection of influenza with rapid culture backup

Test name: Mycoplasma pneumoniae by PCR

ARUP #: 0060256

Methodology: Qualitative Polymerase Chain Reaction

Use:

Determine whether M. pneumoniae is the cause of pneumonia; may help in determining treatment and severity

Test name: Streptococcus pneumoniae Antigen, Urine

ARUP #: 0060228

Methodology: Qualitative Immunochromatographic Assay

Use:

Rapid diagnostic test for invasive disease from S. pneumoniae

Limitations:

False positives may occur because of cross-reactivity with other members of S. mitis group

Clinical correlation is recommended

Patients who have received the S. pneumoniae vaccines may test positive in the 48 hours following vaccination; avoid testing within 5 days of receiving vaccination

Test name: Legionella pneumophila Antigen, Urine

ARUP #: 0070322

Methodology: Qualitative Enzyme-Linked Immunosorbent Assay

Use:

Rapid diagnostic test with good sensitivity and high specificity

Limitations:

Detects L. pneumophila serogroup 1 antigens

Test name: Legionella Species by PCR

ARUP #: 0056105

Methodology: Qualitative Polymerase Chain Reaction

Use:

Rapid diagnostic

Aid in diagnosing etiology of pneumonia when Legionella is suspected

Detect several medically relevant Legionella species including L. pneumophila, L. micdadei, L. bozemanii, L. longbeachae, L. feeleii and L. dumoffii

Increase chances for discovery of organism in patient partially treated with empirical antibiotics

Very high sensitivity and specificity

Limitations:

Only for respiratory secretions

Negative result does not rule out the presence of PCR inhibitors nor the presence of Legionella organisms in numbers lower than the limit of detection

Test name: Chlamydia pneumoniae by PCR

ARUP #: 0060715

Methodology: Qualitative Polymerase Chain Reaction

Use:

Confirm C. pneumoniae as infectious agent in nasal wash, nasopharyngeal aspirate, bronchoalveolar lavage (BAL) or pleural fluid

More sensitive than DFA

Test name: Body Fluid Culture (Includes Gram Stain 0060101)

ARUP #: 0060108

Methodology: Standard reference procedures for bacterial stain, aerobic culture, and identification. Anaerobe culture performed on properly collected specimens

Use:

Positive culture aids in diagnosis of CAP

Test name: Procalcitonin

ARUP #: 0020763

Methodology: Immunofluorescent

Use:

Use in respiratory tract infections to differentiate need to treat with antibiotics

Test name: Blood Culture

ARUP #: 0060102

Methodology: Continuous Monitoring Blood Culture/Identification

Use:

Utility is questionable