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.

Pneumonia%20-%20community-acquired Signs and Symptoms

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 higher in children <5 years old and in adults >60 years of age
  • Occurs more frequently during winter months 
  • More common in men than in women
  • Rates are higher among blacks as compared to Caucasians 
  • In the Asia-Pacific region, mortality is estimated at 1.1-30%, with Japan, India, Philippines, Pakistan, Malaysia and Cambodia having the highest mortality rates
  • Mortality is higher in patients who are hospitalized, with comorbidities, those belonging to low-income countries, in nursing homes or with advanced age

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 ciliostatic 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, pneumolysin, 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 and X-ray may show lobar consolidation, bilateral infiltrates or cavitation
    • Respiratory:
      • Acute cough (nonproductive or productive of purulent or rust-colored sputum)
      • At least 1 abnormal chest finding (eg diminished breath sounds, rhonchi, crackles or wheeze)
    • Systemic: 
      • Pleuritic chest pain
      • Chills or rigors
      • Confusion
    • 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, long-term steroids)
  • Comorbid conditions:
    • Chronic respiratory disease (eg bronchial asthma, chronic bronchitis, cystic fibrosis, bronchiectasis, COPD, pulmonary edema)
    • Genetic disorder (eg Kartagener's syndrome)
    • Influenza
    • Chronic renal disorders
    • Hepatic conditions
    • Diabetes mellitus
    • Malignancy (eg myeloma, lung cancer)
    • Immunocompromised states: Human immunodeficiency virus (HIV) infection, hypogammaglobulinemia (IgG2 immunodeficiency), hyperimmunoglobulin E (Job) syndrome, surgical asplenia or sickle cell disease
  • Continual contact with children (eg young children attending childcare, preschool teachers)
  • Cigarette smoking, alcoholism
  • Elderly (age >65 years old)
  • Immunosuppression, malnutrition
  • 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 jails and human shelters
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