Pneumonia - Community-Acquired Signs and Symptoms

Introduction

• Acute infection of the pulmonary parenchyma accompanied by symptoms of acute illness and abnormal chest findings acquired outside of the hospital setting
• Occurs at highest rates in the very young and elderly
• Potentially life-threatening especially in older adults and those with comorbid disease

• Still the leading cause of death from an infectious disease in adults and in children <5 years old 
• Sixth major cause of morbidity and mortality
• Rate higher in children <5 years old and in adults >60 years of age 
• More common in men than in women
• 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

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 history of 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, Chlamydophila psittaci) and viruses are the other commonly identified pathogens of CAP
  • Viruses may account for 10-20% of cases
• Klebsiella pneumoniae and Burkholderia pseudomallei are present in Southeast Asia
  • K pneumoniae is mostly seen in Taiwan, Thailand, India, Philippines and Malaysia; infrequently found in Europe and America
  • Melioidosis caused by B pseudomallei has been reported in Southeast Asia (ie Malaysia, Thailand, Singapore, Cambodia, Hong Kong), Northern Australia, Taiwan, Southern China, and India
• 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
• Respiratory syncytial virus (RSV) can cause life-threatening lower respiratory tract infection in older persons, immunocompromised patients and those with underlying cardiac or pulmonary disease
  • Patients with severe RSV infection usually present with pneumonia and/or respiratory failure

• 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
  • M 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

• Commonly presents with at least one abnormal chest finding of diminished breath sounds, rhonchi, crackles or wheeze and X-ray may show lobar consolidation with air bronchogram, bilateral/unilateral infiltrates or cavitation (as seen in necrotizing pneumonia)     
  • Respiratory:
    • Acute cough (non-productive or productive of purulent or rust-colored sputum), difficulty of breathing, pleuritic chest pain and at least one abnormal chest finding (eg diminished breath sounds, rhonchi, crackles or wheeze)
  • Systemic: 
    • Chills or rigors
    • Confusion
  • Abnormal vital signs:
    • Respiratory rate (RR) >20 breaths/minute
    • Heart rate (HR) >100 beats/minute
    • Fever >38^oC

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 (DM)
  • 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 (O₂)  and inhalation therapy (particularly containing steroids or using plastic 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