Pneumonia, Community-Acquired

SOURCE

Source: Blackford MG, Glover ML, Reed MD. Lower respiratory tract infections. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey L, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146071234. Accessed January 16, 2017.

DEFINITION

• Lung inflammation caused by bacterial or viral infection.

• Pneumonia developing in patients with no contact to a medical facility.

ETIOLOGY

• Majority of cases in otherwise healthy adults caused by Streptococcus pneumoniae (pneumococcus).

• Atypical pathogens include:

  • Mycoplasma pneumoniae

  • Legionella species

  • Chlamydophila pneumoniae

• Other common pathogens include Haemophilus influenza and a variety of viruses including influenza.

• Staphylococcus aureus and Gram-negative rods causative agents in elderly nursing home patients and in association with alcoholism and other debilitating conditions.

PATHOPHYSIOLOGY

• Microorganisms gain access to lower respiratory tract by three routes:

  • Inhaled as aerosolized particles.

  • Via bloodstream from extrapulmonary site of infection.

  • Aspiration of oropharyngeal contents.

• Viral lung infections suppress bacterial clearing activity of lung by impairing alveolar macrophage function and mucociliary clearance, setting stage for secondary bacterial pneumonia.

EPIDEMIOLOGY

• One of the most common causes of severe sepsis and infectious causes of death in the United States.

• Occurs in persons of all ages, although clinical manifestations most severe in very young, elderly, and chronically ill.

PREVENTION

• Polyvalent polysaccharide vaccines available for S. pneumoniae and H. influenzae type b.

• Annual influenza vaccine.

• Pneumococcal vaccine.

RISK FACTORS

• Age >65 years.

• Diabetes mellitus.

• Asplenia.

• Chronic cardiovascular, pulmonary, renal, and/or liver disease.

• Smoking and/or alcohol abuse.

CLINICAL PRESENTATION

• Clinical appearance similar regardless of etiology.

SIGNS AND SYMPTOMS

• Abrupt onset of:

  • Fever.

  • Chills.

  • Dyspnea.

  • Productive cough.

• Rust-colored sputum or hemoptysis.

• Pleuritic chest pain.

PHYSICAL EXAMINATION

• Tachypnea and tachycardia.

• Dullness to percussion.

• Increased tactile fremitus, whisper pectoriloquy, and egophony.

• Chest wall retractions and grunting respirations.

• Diminished breath sounds over affected area.

• Inspiratory crackles during lung expansion.

DIAGNOSIS

MEANS OF CONFIRMATION AND DIAGNOSIS

• Chest radiograph.

• Sputum examination and culture.

  • Gram stain.

LABORATORY TESTS

• Sputum Gram stain and culture.

• Complete blood count (CBC)

  • Leukocytosis with predominance of polymorphonuclear cells.

• Arterial blood gas or pulse oximetry.

  • Low oxygen saturation.

IMAGING

• Chest radiograph: dense lobar or segmental infiltrate.

DIAGNOSTIC PROCEDURES

• Sputum induction and bronchoscopy for patients who cannot provide expectorated samples.

DIFFERENTIAL DIAGNOSIS

• Influenza

• Bronchitis

• Lung abscess.

DESIRED OUTCOMES