Pneumonia

Pneumonia :
1. Epidemiology
a. Classified as community-acquired or nosocomial (hospital-acquired)
b. Community-acquired pneumonia is further subdivided into typical and atypical.
2. Typical community-acquired pneumonia
c. Epidemiology
* (1) Majority are caused by bacterial pathogens.
* (2) Most often due to Streptococcus pneumoniae (50-75%;Streptococcus pneumoniae: most common cause of typical community-acquired pneumonia
d. Pathogenesis
* (1) Inhalation of aerosol from an infected patient
* (2) Aspiration of nasopharyngeal flora while sleeping
e. Bronchopneumonia
* (1) Begins as an acute bronchitis and spreads locally into the lungs
* (2) Usually involves the lower lobes or rightmiddle lobe
* (3) Lung has patchy areas of consolidation .
* Bronchopneumonia: acute bronchitis lung parenchyma
* Microabscesses are present in the areas of consolidation.
f. Lobar pneumonia
* Complete or almost complete consolidation of a lobe of lung
g. Complications
* (1) Lung abscesses, empyema (pus in the pleural cavity)* (2) Sepsis
h. Clinical findings
* (1) Sudden onset of high fever with productive cough
* (2) Chest pain
* (3) Tachycardia
* (4) Signs of consolidation (alveolar exudate)
Typical pneumonia: signs of consolidation (alveolar exudate)
* (a) Dullness to percussion
* (b) Increased vocal tactile fremitus
*Sound is transmitted well through alveolar consolidations.
* (c) Late inspiratory crackles
* (d) Bronchial breath sounds
* (e) Bronchophony and egophony
* (5) Chest radiograph (gold standard screen)
Chest radiograph: gold standard for diagnosing pneumonia
* (a) Patchy infiltrates (bronchopneumonia) or lobar consolidation
*(b) Sensitivity 50% to 85%
* (6) Laboratory findings
* (a) Positive Gram stain
Positive Gram stain: more useful than culture
* More useful than culture
* Cultures are still obtained.
* Sensitivity 80%
* (b) Neutrophilic leukocytosis
* (c) Blood cultures positive in 20% of cases.
1. Atypicalcommunity-acquired pneumonia
a. Epidemiology
* (1) Usually caused by Mycoplasma pneumoniae
Mycoplasma pneumoniae: most common cause of atypical pneumonia
* (2) Other pathogens
* (a) Chlamydophilia pneumoniae
* (b) Viruses
* Respiratory syncytial virus, influenzavirus, adenovirus
* (c) Chlamydia trachomatis innewborns
a. Pathogenesis
* Contracted by inhalation (droplet infection)
b. Patchy interstitial pneumonia
Atypical pneumonia: interstitial pneumonia; no signs of consolidation
* (1) Mononuclear infiltrate
* (2) Alveolar spaces usually free of exudate
c. Clinical findings
* (1) Insidious onset, low-grade fever
* (2) Nonproductivecough
* (3) Chest pain
* (4) Flu-like symptoms
* Pharyngitis, laryngitis, myalgias, headache
* (5) No signs of consolidation
1. Nosocomial pneumonia
d. Epidemiology; risk factors:
* (1) Severe underlying disease
* (2) Antibiotic therapy
* (3) Immunosuppression
* (4) Respirators
* Most commonsource of infection
e. Pathogens
* (1) Gram-negative bacteria
* Pseudomonas aeruginosa (respirators), Escherichia coli
Pseudomonas aeruginosa: nosocomial pneumonia; contracted from respirators
* (2) Gram-positive bacteria (e.g., Staphylococcus aureus)
2. Pneumonia in immunocompromised hosts
f. Complication of AIDS and bone marrow transplantation...