What you need to know:
Community acquired pneumonia (CAP) is diagnosed in outpatients that do not reside in skilled nursing facilities, or those that were admitted to the hospital less than 48 hours prior. Over 5 million cases of CAP occur in the United States on an annual basis. About 20% of these patients require hospitalization, and as many as 55,000 patients die each year due to their illness. The very young and the very old are at greatest risk for severe complications and death related to CAP. Risk factors for CAP include underlying lung disease, heart failure, immunosuppression, alcoholism, and age >70 years.
The differential for CAP is broad and depends on the patient’s history and underlying comorbid conditions. Overall, Streptococcus pneumoniae is the most common causative organism. Other potential bacterial pathogens include, but are not limited to Staphylococcus aureus, Haemophilus influenzae, Klebsiella pneumoniae, Pseudomonas aeruginosa, Mycoplasma pneumoniae, and Legionella species. In addition to bacteria, viruses such as Influenza and Respiratory Syncytial Virus (RSV) may cause pneumonia. Much less often, fungi may cause invasive pneumonia. It is also possible for individuals to develop post-viral pneumonia following Influenza infection.
Symptoms of CAP often include fever, chills, pleuritic chest pain, cough, sputum production, fatigue, and myalgias. The symptoms are often vague and patients may or may not report chest pain and sputum production. The absence of these symptoms does not exclude the diagnosis.
ACM Resources to help you learn more:
"Pneumonia" in Harrison's Principles of Internal Medicine, 19e
"Pulmonary Disorders" in Current Medical Diagnosis & Treatment 2018
Community-acquired Pneumonia in McGraw-Hill's Diagnosaurus 4.0