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Emergency And Acute Medicine – Pneumonia in Adults
Pneumonia in adults is an acute infection of the lung parenchyma and is the seventh leading cause of death and the leading infectious cause of mortality in the United States. Mortality is highest in elderly patients and those with chronic heart, lung, liver, or kidney disease, diabetes mellitus, alcoholism, malignancy, asplenia, immunosuppression, or recent antimicrobial use. Pneumonia is classified by source as community-acquired (CAP), healthcare-associated (HCAP), hospital-acquired (HAP), or ventilator-associated (VAP), and by presentation as typical or atypical. Complications include bacteremia, sepsis, lung abscess, empyema, and respiratory failure.
The most common cause of community-acquired pneumonia is Streptococcus pneumoniae. Other typical CAP pathogens include Haemophilus influenzae, Klebsiella pneumoniae, Moraxella catarrhalis, Streptococcus pyogenes, and Staphylococcus aureus. Atypical CAP pathogens include Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella pneumophila, and respiratory viruses. Healthcare- and hospital-associated pneumonias are more commonly caused by gram-negative organisms such as Pseudomonas and Stenotrophomonas, as well as methicillin-resistant Staphylococcus aureus (MRSA). Immunocompromised patients are at risk for organisms such as Mycobacterium tuberculosis and Pneumocystis jirovecii. Aspiration pneumonia may involve chemical pneumonitis with or without oral and gastric anaerobes.
Typical pneumonia presents with acute onset of fever, chills, rigors, productive cough, dyspnea, and pleuritic chest pain. Atypical pneumonia has a more subacute onset with a viral prodrome, nonproductive cough, low-grade fever, headache, myalgias, and malaise, often without pleuritic pain or rigors. On examination, patients may demonstrate tachypnea, tachycardia, hypoxia, and fever. Lung findings can include dullness to percussion, increased tactile fremitus, egophony, rales, rhonchi, or decreased breath sounds, although pneumonia may be present without classic consolidation findings. Elderly patients frequently present atypically, sometimes with confusion or functional decline as the primary symptom.
Diagnosis is based on clinical findings supported by imaging. Laboratory evaluation generally includes a complete blood count and serum chemistry panel. Blood and sputum cultures are typically reserved for ICU patients. Urine antigen testing for S. pneumoniae and Legionella may be helpful in select cases. Lactate levels may assist in identifying sepsis. Chest radiography is the primary imaging modality and may demonstrate consolidation, air bronchograms, interstitial infiltrates, pleural effusion, empyema, or cavitation. Radiographic findings are nonspecific for particular pathogens. Imaging may be deferred in young, healthy patients treated empirically as outpatients, and a negative radiograph does not exclude pneumonia if clinical suspicion is high.
Initial management includes supplemental oxygen, IV access, fluid resuscitation when indicated, cardiac monitoring, bronchodilators if bronchospasm is present, and airway management in cases of severe respiratory distress. Empiric antibiotic therapy should follow established guidelines. Previously healthy outpatients may receive azithromycin or doxycycline. Patients with significant comorbidities should receive a β-lactam plus macrolide combination or a respiratory fluoroquinolone alone. Inpatients not requiring ICU care may receive a β-lactam plus macrolide or a respiratory fluoroquinolone. ICU patients should receive a β-lactam plus either a macrolide or respiratory fluoroquinolone, with additional coverage for Pseudomonas or MRSA when risk factors are present. Aspiration pneumonia may require anaerobic coverage such as clindamycin or metronidazole. Prompt antibiotic administration is critical in ill-appearing patients.
Disposition decisions are guided by clinical judgment and validated tools such as the CURB-65 score and the Pneumonia Severity Index. CURB-65 evaluates confusion, elevated BUN, respiratory rate ≥30, hypotension, and age ≥65. Scores of 0–1 generally support outpatient management, while higher scores favor admission and possible ICU care. Admission is also indicated for unstable vital signs, hypoxia, significant comorbidities, failure of outpatient therapy, or inability to ensure follow-up. Discharge may be appropriate for patients younger than 65 without comorbidities, with normal vital signs and reliable follow-up within 72 hours.
Clinicians must avoid delays in antibiotic initiation in critically ill patients and remain vigilant for pneumonia in those presenting with presumed exacerbations of chronic lung disease. Tuberculosis and HIV risk factors should always be assessed. Elderly and immunocompromised patients may lack classic symptoms, making a high index of suspicion essential for timely diagnosis and management.
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