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Community-acquired Pneumonia

Community-acquired pneumonia affects about 4 million patients each year. About 20% of these cases require hospitalization, the condition. Mortality rates range from 1% to 5% in outpatients.

Pathophysiology

Pathogens in community-acquired pneumonia include Streptococcus pneumoniae (33%), Haemophilus influenzae (10%), Legionella species (7%), and Chlamydia pneumoniae (5%) Other organisms include Mycoplasma pneumoniae, other gram-positive organisms, gram-negative organisms, anaerobes, mycobacteria, fungi, and viruses. S pneumoniae is the leading cause of community-acquired pneumonia.

Factors that increase susceptibility to pneumonia include age over 65 years, the presence of chronic underlying illness, and certain local epidemiologic. More than half of cases occur in patients over age 65.

Factors that increase risk of death

Age over 65 also increases the risk of death from community-acquired pneumonia. Additional risk factors for death from this condition include the following:

Multilobar, necrotizing, aspiration, or postobstructive infection

Abnormal vital signs, particularly a respiratory rate of 30 breaths/minute or more.

Clinical evaluation

Outpatient treatment of community-acquired pneumonia is largely empirical. All patients should have a chest film taken, since a diagnosis of pneumonia cannot be established in the absence of infiltrates.

Outpatient therapy for community-acquired pneumonia

Antibiotics should be chosen that provide adequate coverage against the presumed organisms known to cause community-acquired pneumonia. A macrolide is recommended, including erythromycin, clarithromycin (Biaxin), or azithromycin (Zithromax); the fluoroquinolones levofloxacin (Levaquin), trovafloxacin mesylate (Trovan), grepafloxacin (Raxar), sparfloxacin (Zagam), and any other fluoroquinolone with enhanced activity against S pneumoniae; and (in patients between the ages of 17 and 40) doxycycline.

Duration of therapy should be 7 to 10 days.