Community-acquired Pneumonia in Adults

Background

• Community-acquired pneumonia (CAP) is a lower respiratory tract infection due to 1 or more pathogens acquired outside of a hospital setting. This is in contrast to pneumonias acquired within the hospital setting, including hospital-acquired pneumonia and ventilator-associated pneumonia.
• The incidence of CAP ranges from 10.6 to 44.8 cases per 1,000 person-years and increases with age.
• Risk factors for CAP include age; smoking; chronic comorbidities, such as diabetes mellitus, chronic lung (COPD, bronchitis, asthma, etc.), renal, heart, or liver disease; orodental/periodontal disease; treatment with proton pump inhibitors; prescription opioids; and high alcohol consumption.
• Pathogens that cause CAP include respiratory viruses, Streptococcus pneumoniae, Mycoplasma pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Chlamydophila pneumoniae, Legionella species, Staphylococcus aureus, and gram-negative rods.
• Complications of pneumonia include parapneumonic effusion, empyema, lung abscess, sepsis, and cardiac complications, such as heart failure, cardiac arrhythmias, and acute coronary syndromes.
• Lower respiratory tract infections are among the top 4 causes of death, and the most common infectious cause of death, worldwide.
• Mortality rate is highly variable, ranging from < 1% to > 30% depending on comorbidities and findings at presentation.
• Key preventive measures include vaccination for influenza and S. pneumoniae and smoking cessation (Strong recommendation).

Evaluation

• Clinical features associated with CAP include:
  • fever and chills
  • cough, increased sputum production, chest pain, and shortness of breath
  • malaise and myalgia
• Physical exam may reveal dullness to percussion, crackles, egophony, tachypnea, and increased tactile fremitus.
• Findings may be more subtle in some patients, such as the elderly, who may present with confusion and minimal respiratory symptoms.
• Chest imaging showing infiltrates, in addition to suggestive clinical features, is required for diagnosis (Strong recommendation).
• Additional imaging may include computed tomography (CT) in cases of severe, unresolving pneumonia where additional intervention is considered and ultrasound to further assess for fluid with concern for empyema.
• Laboratory findings may include leukocytosis, leukopenia, thrombocytopenia, hepatic or renal dysfunction; leukopenia and thrombocytopenia are associated with poor prognosis.
• Blood cultures and sputum cultures are recommended for hospitalized patients with, or at risk for, severe disease and complications; cultures should be collected before the start of antibiotics (Strong recommendation).
• Urinary antigen tests for S. pneumoniae and Legionella pneumophila serogroup 1 are recommended for patients with severe CAP (Strong recommendation).
• Additional testing for specific pathogens based on clinical and epidemiologic clues is recommended if a positive result would change management of CAP (Strong recommendation), such as testing for influenza.
• Scoring systems and guideline criteria have been developed to help predict short-term mortality and the need for hospital or intensive care unit (ICU) admission (see also Pneumonia Severity Assessment).

Management

• Recommendations for antibiotic therapy vary with the treatment setting, the risk factors for severe disease, and the likelihood of infection with a drug-resistant organism.
• First-line options for outpatients:
  • If the patient is otherwise healthy and without risk factors for drug-resistant organisms (including no use of antibiotics within previous 3 months), use:
    • amoxicillin 1 g orally 3 times daily (Strong recommendation)
    • if pneumococcal resistance to macrolides known to be < 25%, may use
      • azithromycin 500 mg orally on first day followed by 250 mg orally once daily for duration of therapy
      • clarithromycin 500 mg orally twice daily
      • clarithromycin extended release 1,000 mg orally once daily
    • doxycycline 100 mg orally twice daily (Some areas of the United States have significantly higher than average tetracycline resistance rates, do not use doxycycline in areas with S. pneumoniae tetracycline resistance > 25%).
  • If the patient has chronic comorbidities (such as diabetes mellitus; heart, lung, liver, or renal disease; or immunocompromise), recent antibiotic use (within previous 3 months), or is in an area with high rates (> 25%) of macrolide-resistant S. pneumoniae, use either:
    • monotherapy with a respiratory fluoroquinolone (Strong recommendation), such as, levofloxacin 750 mg orally once daily, moxifloxacin 400 mg orally once daily, or gemifloxacin 320 mg orally once daily
    • combination therapy with either
      • amoxicillin/clavulanate 500 mg/125 mg orally 3 times daily, 875 mg/125 mg orally twice daily, or 2,000 mg/125 mg orally twice daily
      • a cephalosporin, such as, cefpodoxime 200 mg orally twice daily or cefuroxime 500 mg orally twice daily
    • PLUS either
      • a macrolide, such as, azithromycin 500 mg orally on first day then 250 mg orally once daily or clarithromycin (500 mg orally twice daily or extended release 1,000 mg orally once daily) (Strong recommendation) OR
      • doxycycline 100 mg orally twice daily (Weak recommendation)
  • In outpatients also diagnosed with influenza consider oseltamivir independent of duration of illness before diagnosis (Weak recommendation).
• First-line options for inpatients:
  • A respiratory fluoroquinolone, such as, levofloxacin 750 mg IV or orally once daily or moxifloxacin 400 mg IV or orally once daily (Strong recommendation).
  • A beta-lactam plus a macrolide, such as, ceftriaxone 1-2 g IV once daily plus azithromycin (Strong recommendation).
  • If suspicion of:
    • Pseudomonas infection, consider use of an antipneumococcal, antipseudomonal agent, such as, cefepime or piperacillin-tazobactam plus a fluoroquinolone, such as, levofloxacin
    • methicillin-resistant S. aureus (MRSA), consider addition of vancomycin or linezolid
  • Treat patients until they are clinically stable and for a period of ≥ 5 days (Strong recommendation).
  • Among inpatients also diagnosed with influenza give oseltamivir independent of duration of illness before diagnosis (Strong recommendation).