pneumonia (PNA)

Introduction

Infection of the pulmonary parenchyma.

Etiology

• bacterial pneumonia
  • community-acquired: Streptococcus pneumoniae
    • 90% of identified bacterial isolates in adults
    • 95% of identified isolates in preantibiotic era
    • 10-15% of inpatient cases in the United States*
  • nosocomial (60% gram-negative bacilli)
  • Mycobacterium tuberculosis
  • rickettsiae
  • common variable immunodeficiency
  • other
• viral pneumonia
  • > 20% of severe pneumonia with respiratory failure requiring mechanical ventilation due to viral pneumonia
• fungal pneumonia
  • Pneumocystis carinii (AIDS)
• aspiration pneumonia
• eosinophilic pneumonia
• interstitial pneumonia
• postobstructive pneumonia
  • bronchial neoplasm, foreign body, bronchial stricture
• nosocomial pneumonia
• community-acquired pneumonia

* see etiology of pneumonia & community-acquired pneumonia

* also see characteristics of etiologic agents of pneumonia

* ACE inhibitors, but not ARBs may play protective role

Epidemiology

• compromised hosts are particularly vulnerable
• pneumonia accounts for 10% of admissions to hospital wards & is still a common cause of death

Pathology

• the most common mechanism for acquiring pneumonia is aspiration of organisms from the oropharynx
  • aerobic gram-positive cocci & anaerobes most common
  • 50% of adults aspirate during sleep
  • aspiration increases with:
    • impaired consciousness
    • neurologic disorders
    • nasogastric or endotracheal tubes
• less common mechanisms
  • inhalation of infected particles
  • hematogenous or contiguous spread from another infected site
  • open trauma to chest
• alterations in host defenses contribute to the pathophysiology of pneumonia
  • abnormal mucociliary function
  • decreased IgA allowing adherence of bacteria to airways
  • compromised cellular immunity
  • compromised humoral immunity
• severity of pneumococcal pneumonia associated with bacterial load

History

• onset, duration, systemic symptoms, fever, weight loss, other medical conditions, recent antibiotic use, travel history, exposure to animals, tuberculosis history, sick contacts, alcohol/other drug use, HIV risk factors, occupational history

Clinical manifestations

• fever
• tachycardia
• postural changes
• tachypnea may be only sign in elderly
  • may present as delirium, confusion, & falls in the elderly
• rales, pulmonary crackles
• egophony
• inspiratory chest expansion lag on affected side
• splinting
• increased fremitus
• dullness to percussion
• bronchial breath sounds
• bronchophony

Laboratory

• Sputum
  • gram stain
    • > 5 epithelial cells per low power field suggests oral-pharyngeal rather than pulmonary secretions
    • > 25 neutrophils per low power field suggests lower respiratory tract infection
    • can lead to diagnosis in 15-45% of cases
  • culture
    • no anaerobic cultures because of contamination from pharyngeal anaerobes
    • cultures can be misleading
  • fluorescent antibody studies
    • Legionella pneumophila
  • multiplex PCR assay may become the new standard
• Complete blood count
  • leukocyte count
    • may be low or normal in the elderly or immunocompromised
    • a leukocyte count < 10,000/mm3 is common in Mycoplasma pneumonia
• blood cultures
  • for all hospitalized patients with pneumonia
  • 20-30% of patients with bacterial pneumonia have positive blood cultures
• arterial blood gas
• chemistry profile
  • electrolytes
  • liver function tests
  • renal function tests
  • serum glucose
  • serum C-reactive protein (> 30 mg/dL = high risk) + serum procalcitonin improves diagnostic accuracy
  • serum procalcitonin > 0.1 ng/mL suggest bacterial pneumonia rather than heart failure
• serologic studies
  • coccidioidomycosis titers
  • Mycoplasma titers
  • HIV testing

Diagnostic procedures

• invasive procedures may be indicated in treatment failures or suspected non-bacterial origin of severdisease
• transtracheal aspiration
• transthoracic needle aspiration (thoracentesis)
• fiberoptic bronchoscopy generally after CT
  • bronchial brushings
  • bronchoalveolar lavage or endotracheal aspiration
  • transbronchial biopsy
• open lung biopsy
• induced sputum or Lukens trap

Radiology

chest radiograph

• lobar
  • Streptococcus pneumonia
  • Haemophilus influenza
• interstitial
  • Mycoplasma pneumonia
  • viral pneumonia
• bilateral
  • aspiration
• cavitary
  • Mycobacterium tuberculosis
  • Klebsiella pneumonia
  • Staphylococcus aureus
  • Pseudomonas aeruginosa
• radiographic resolution lags behind clinical improvement
• follow-up chest X-rays 8 weeks after onset
  • to show resolution & absence of underlying lung cancer
  • may not be necessary in younger patients

lung ultrasound may be alternative to chest X-ray

CT of thorax is 'gold standard'

Complications

• pleural (parapneumonic) effusion - thoracentesis
• empyema - requires chest tube drainage
• abscess formation (empyema)
• pericarditis (purulent)
• adult respiratory distress syndrome (ARDS)
• sepsis with DIC
• multi-organ failure
• increased risk of myocardial infarction, stroke
  • RR=5-12 for pneumococcal pneumonia, influenza

Also see poor prognostic factors & criteria for severe pneumonia

• disease interaction(s) of pneumonia with dementia
• disease interaction(s) of obstructive sleep apnea (OSA) with pneumonia
• disease interaction(s) of stroke with pneumonia

Management

• supportive measures
  • hydration
  • oxygen
  • noninvasive positive pressure ventilation may reduce need for endotracheal intubation
• empiric antimicrobial therapy
  • community-acquired pneumonia in adults (see community-acquired pneumonia)
  • nosocomial pneumonia
    • etiology: most frequently:
      • gram negative organisms
      • Staphylococcus
      • Legionella
    • empiric therapy:
      • ceftriaxone or cefotaxime plus an aminoglycoside
      • mezlocillin or ceftazidime plus an aminoglycoside if Pseudomonas is likely (ICU setting or immunocompromised host)
      • dual coverage for Pseudomonas if suspected - Cefepime, imipenem, meropenem, or Zosyn plus an aminoglycoside plus a fluoroquinolone* - fluoroquinolone plus an aminoglycoside or aztreonam if Pseudomonas is suspected - dual Pseudomonas* coverage if growth from respiratory culture in past year - single agent appropriate if antibiotic sensitivity known
  • aspiration pneumonia
    • community-acquired: anaerobes & gram-positive cocci
    • nosocomial: gram-negative organisms & S. aureus
    • empiric therapy: (see aspiration pneumonia)
      • fluoroquinolone alone (trovafloxacin)
        • adding clindamycin increases risk of C difficile without benefit
      • fluoroquinolone plus metronidazole
      • penicillin/beta-lactamase inhibitor + azithromycin
  • pneumonia in adults with cystic fibrosis
  • switching to oral therapy
    • patient is afebrile and stable
    • patients with bacteremia & other medical problems may need longer IV antibiotic therapy
    • for children discharged from the hospital with complicated pneumonia (pneumonia with pleural effusion), IV antibiotics offers no advantage over oral antibiotics
• oral glucocorticoids of no benefit to adults without chronic obstructive pulmonary disease
  • also see community-acquired pneumonia
• prevention:
  • immunization with PCV13 & PPSV23
    • decline in pneumococcal pneumonia due to:
    • widespread use of pneumovax in adults
    • use of pneumococcal conjugate vaccine in children
    • decreased rates of cigarette smoking
  • effective & consistent oral hygiene may reduce incidence of pneumonia in nursing home residents

* Some fluoroquinolones are not recommended for empiric antimicrobial activity in pneumonia because of unreliable activity against Streptococcus pneumoniae. Fluoroquinolones with enhanced activity against Streptococcus pneumonia include:

• levofloxacin
• sparfloxacin
• trovafloxacin
• grepafloxacin
• moxifloxacin
• gatifloxacin
• gemifloxacin

Antimicrobial therapy for pneumonia caused by specific organisms (select or see specific organism)

Response to therapy

• most patients will show clinical improvement within 48-72 hours
• fever & leukocytosis generally resolves by day 4
• consider empyema if response to therapy poor
• chest X-ray often lags behind clinical improvement
• follow-up chest X-ray to show resolution (8-12 weeks after onset)
• weeks to months may be necessary for complete resolution of symptoms

Duration of therapy: (bacterial pneumonia)

• 2 to 3 weeks
• 8 days equivalent to 15 days for ventilator-associated pneumonia

Also see treatment failure

Notes

• readmissions are more common with:
  • comorbidities, including diabetes mellitus, COPD, malignancies, & immunosuppression
  • healthcare-associated pneumonia rather than community-acquired pneumonia
• predictors of readmission:
  • admission from a nursing home or long-term care facility
  • immunosuppression
  • prior antibiotic therapy
  • hospitalization during the past 90 days

More general terms

• lung disease
• pulmonary infection

More specific terms

• aspiration pneumonia
• bacterial pneumonia
• chronic pneumonia
• community-acquired pneumonia (CAP)
• eosinophilic pneumonia; Andrews syndrome; pulmonary eosinophilia
• interstitial pneumonia
• nosocomial pneumonia; hospital-acquired pneumonia; health care-associated pneumonia
• nursing home associated pneumonia
• postobstructive pneumonia
• recurrent pneumonia
• viral pneumonia

Additional terms

• characteristics of etiologic agents of pneumonia
• etiology of pneumonia
• poor prognostic factors & criteria for severe pneumonia
• pulmonary infiltrate in immunocompromised host
• treatment failure, pneumonia

Patient information

pneumonia patient information