Community-acquired pneumonia (CAP) refers to pneumonia contracted outside the health care setting. According to one estimate noted in the most recent Infectious Disease Society of America/American Thoracic Society (IDSA/ATS) consensus guidelines,¹ 915,900 episodes of CAP occur each year in the United States in adults 65 years of age or older.² Furthermore, 20% of all those who develop CAP will require hospitalization, and those with severe CAP may require mechanical ventilation and aggressive multiorgan support.³

Clinical presentation of CAP may be typical or atypical. The typical presentation is associated with rapid onset of fever, productive cough, shortness of breath, clinical signs of pulmonary consolidation (abnormal breath sounds, dullness on percussion), and occasionally pleuritic chest pain.⁴ CAP is usually the result of infection by a common bacterial pathogen such as Streptococcus pneumoniae. Atypical pneumonia is usually attributed to less common bacterial, viral, and fungal pathogens that colonize in susceptible individuals, such as the elderly or immunocompromised.⁵ It has a more gradual onset of dry cough and shortness of breath than typical forms of pneumonia and the patient may experience general myalgias and fatigue.⁴ Despite seemingly insignificant pulmonary presentation, the chest radiograph is abnormal in atypical pneumonia.

The infecting agent in CAP may be bacterial, viral, or fungal. In otherwise healthy adults (younger than age 60), Streptococcus pneumoniae and Hemophilus influenzae are common causative agents in CAP.⁵ Bacterial agents such as Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella pneumophilia are seen in atypical CAP, as well as viruses (eg, influenza virus, respiratory syncytial virus [RSV], and cytomegalovirus [CMV]). Infections by fungi (eg, Pneumocystis carinii) are responsible for a small number of CAP cases and are more likely to occur in immunocompromised patients.⁶

Several different risk factors are associated with CAP, ranging from patient demographics to concomitant illnesses. Currently, the Pneumonia Severity Index (PSI) is one of two main tools available in emergency departments and outpatient settings to determine the severity of CAP. With the PSI model, patient risk scores are determined on the basis of four risk categories: demographic factors, comorbid conditions, findings on physical examination, and laboratory results (eg, pH, blood urea nitrogen [BUN], Sodium, Glucose, hematocrit, and Po₂). Points accumulated within each category are totaled and stratified to one of five risk classes, which correlate to a percent risk of mortality. For a patient with the lowest risk (class I), outpatient treatment is recommended, whereas for a patient found to be at high risk (class IV or V), inpatient treatment is recommended.

The other main pneumonia scoring tool is the CURB65. It is simpler than the PSI and was created for quick and easy use in the emergency department or outpatient office. A patient is assigned 1 point for each of five clinical criteria. A score of 1 or 2 would indicate that an individual can safely be treated as an outpatient, whereas scores of 3 to 5 would suggest inpatient treatment. The five clinical criteria are as follows:

When a patient is admitted to the hospital for CAP, a chest radiograph should be performed on admission and is essential for detecting pulmonary infiltrates. Complete blood counts and routine chemistries should also be performed, as well as two sets of pretreatment blood cultures. CAP consensus guidelines also support pretreatment Gram stain and culture on expectorated sputum for inpatients. For patients with severe CAP requiring intubation, an endotracheal aspirate for sputum analysis should be obtained.⁷ In addition, urinary antigen testing for Legionella pneumophilia and Streptococcus pneumonia should be performed for patients with severe CAP. If pandemic influenza is suspected, specific flu testing may be indicated.

Antibiotic therapy is the main treatment for CAP, with the ultimate goal of killing the infection and resolving the clinical disease. Prompt administration of antibiotic therapy is crucial to favorable CAP outcomes. Early initiation of antibiotics for patients admitted for CAP has been shown to be the single factor most associated with decreased mortality.⁹ For patients admitted through the emergency department (ED), the current IDSA/ATS consensus guidelines recommend the first antibiotic dose be administered before the patient leaves the ED.

As a rule, the most potent drugs within a class are preferred, thus helping reduce bacterial selection for antibiotic resistance. Lack of prompt and effective treatment, inappropriate antibiotic choice, or even an insufficient dose with the appropriate antibiotic have all been shown to encourage antibiotic resistance.³ This may explain why methicillin-resistant Staphylococcus aureus (MRSA) has been found to be an occasional causative agent in CAP.

Early in treatment, the infecting agent is often unknown; therefore, broad-spectrum antibiotic therapy may be indicated initially. Empiric antibiotic selection is based on several factors, including age, antibiotic tolerance, comorbidities, concurrent medications, and epidemiologic setting.⁵ The IDSA/ATS consensus guidelines make several recommendations based both on patient clinical risks and site of treatment. Intravenous antibiotic therapy is recommended for initial treatment of all individuals requiring inpatient hospital admission, with clear regimen differences between acute and critically ill patients.⁷ Once the etiology of CAP has been identified, antimicrobial therapy should be tailored to target the pathogen.

Patients treated with intravenous antibiotics should be switched over to oral medication as soon as clinically possible. This will depend on how the patient is improving clinically, with consideration for such factors as hemodynamic stability, state of the gastrointestinal tract, and ability to ingest medication.⁷ According to the IDSA/ATS guidelines, duration of treatment will depend on whether or not the initial antibiotic treatment was active against the infecting pathogen, or if complicating extrapulmonary infections were present. At minimum, 5 days of treatment is recommended; the patient must not only be afebrile for 48 to 72 hours, but must also meet no more than one CAP-associated sign of instability.⁷ The following are criteria for clinical instability in CAP: