pneumonia%20-%20community-acquired
PNEUMONIA - COMMUNITY-ACQUIRED
Community-Acquired Pneumonia (CAP) is an acute infection of the pulmonary parenchyma accompanied by symptoms of acute illness and abnormal chest findings.
It is a lower respiratory tract infection acquired in the community within 24 hours to <2 weeks or occurring ≤48 hours of hospital admission in patients who do not meet the criteria for healthcare-associated pneumonia.
It occurs at the highest rates in the very young and the very old.
Potentially life-threatening especially in older adults and those with comorbid disease.

Introduction

Community-Acquired Pneumonia (CAP)

  • Acute infection of the pulmonary parenchyma accompanied by symptoms of acute illness and abnormal chest findings 
  • Occurs at highest rates in the very young and the very old
  • Potentially life-threatening especially in older adults and those with comorbid disease
Epidemiology
  • Still the leading cause of death from an infectious disease in adults and in children <5 years old 
  • 6th major cause of morbidity and mortality
  • Rate increases as the age increases 
  • Occurs more frequently during winter months 
  • Commonly occurs in men than in women 
  • Rates are higher among blacks as compared to Caucasians 
  • Mortality is higher in patients who are hospitalized 

Definition

  • Lower respiratory tract (LRT) infection acquired in the community within 24 hours to <2 weeks or occurring ≤48 hours of hospital admission in patients who do not meet the criteria for healthcare-associated pneumonia (HCAP)

Etiology

  • In most patients with community-acquired pneumonia (CAP), the causative organism is not known
  • Success rate in determining the etiologic agent is usually about 50%
  • Streptococcus pneumoniae is the most frequently isolated organism
  • Drug-resistant S pneumoniae (DRSP) may be found in patients with antibiotic use within the past 3 months, alcoholism, >65 years old, immunosuppression or resident of nursing home
  • Haemophilus influenzae, atypical pathogens (eg Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella pneumophila, and Chlamydophila psittaci) and viruses are the other commonly identified pathogens of CAP
    • Viruses may account for 10-20% of cases
  • Gram-negative bacilli (Enterobacteriaceae and Pseudomonas aeruginosa) are frequent causative agents in patients who have had previous antimicrobial treatment or who have pulmonary comorbidities [eg bronchiectasis or chronic obstructive pulmonary disease (COPD)]
  • Anaerobes are usually associated with aspiration pneumonia
Pathophysiology
  • The development of CAP may be due to microaspiration, presence of defect in the host defenses, possible exposure to a virulent microorganism, or due to presence of an overwhelming inoculum
    • Microaspiration is a mechanism by which the constituents of both the microbiota and pathogens reaches the lungs
    • Hematogenous spread, contiguous spread and macroaspiration are the other mechanisms that a pathogen may gain access to the lungs
  • Virulence factors: 
    • Chlamydia pneumoniae - possesses cilistatic factor
    • Mycoplasma pneumoniae - shears off the cilia
    • Influenza virus - causes marked reduction on the tracheal mucus velocity for up to 12 weeks postinfection
    • S pneumoniae and Neisseria meningitides - produces proteases and splits secretory IgA
    • Other virulence factors: Inhibition of phagocytosis, pneumolysis, thiol-activated cytolysin
    • Mycobacterium spp, Nocardia spp, and Legionella spp - resistant to microbicidal activity (phagocytes)

Signs and Symptoms

  • It commonly presents with any of the typical signs and symptoms listed below with at least 1 abnormal chest finding of diminished breath sounds, rhonchi, crackles or wheeze
    • Acute cough (nonproductive or productive of purulent or rust-colored sputum)
    • Pleuritic chest pain
    • At least 1 abnormal chest finding (eg diminished breath sounds, rhonchi, crackles or wheeze)
    • Chills or rigors
    • Abnormal vital signs:
      • Respiratory rate (RR) >20 breaths/minute
      • Heart rate (HR) >100 beats/minute
      • Fever >37.8oC

Risk Factors

  • Alterations in the level of consciousness that predisposes to both macroaspiration of stomach contents and microaspiration of upper airway secretions during sleep
  • Administration of immunosuppressive agents (eg recipients of solid organ or stem cell transplant or those receiving chemotherapy)
  • Elderly (age >70 years)
  • Immunosuppression, malnutrition
  • Comorbid conditions [eg bronchial asthma, chronic bronchitis, cystic fibrosis, bronchiectasis, COPD, Kartagener's syndrome, influenza, lung cancer, pulmonary edema, chronic renal disorders, hepatic conditions, diabetes mellitus, neoplastic diseases, human immunodeficiency virus (HIV) infection, myeloma, hypogammaglobulinemia (IgG2 immunodeficiency), hyperimmunoglobulin E (Job) syndrome, surgical asplenia or sickle cell disease] 
  • Continual contact with children
  • Cigarette smoking, alcoholism
  • Sudden changes of temperature at work
  • Medications (eg inhaled corticosteroids, proton pump inhibitors and H2 blockers, antipsychotic drugs, and sedatives) 
  • Oxygen and inhalation therapy (particularly containing steroids or using plastic pear-spacers)
  • Other risk factors for young adults: Military trainees and presence of low cholesterol or albumin levels
  • People who are homeless and overcrowding inside the jail and men's shelter
  • Sudden changes of temperature at work
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