What are the key clinical features that differentiate hospital-acquired pneumonia (HAP) from community-acquired pneumonia (CAP)?

Key clinical features differentiating hospital-acquired pneumonia (HAP) from community-acquired pneumonia (CAP) include the timing of onset, patient setting, and typical causative pathogens, which influence clinical presentation and management.

HAP is defined as pneumonia developing 48 hours or more after hospital admission, in a patient who did not have incubating pneumonia at admission, whereas CAP occurs outside the hospital or in nursing home residents and is present at or within 48 hours of admission ¹.

Clinically, both HAP and CAP present with symptoms of lower respiratory tract infection such as cough, sputum production, breathlessness, fever, and chest discomfort or pain; however, HAP patients often have more severe illness due to underlying comorbidities, recent invasive procedures, or immunosuppression associated with hospitalization ¹.

Vital sign abnormalities such as increased respiratory rate, tachycardia, hypotension, and hypoxia are common in both but may be more pronounced in HAP due to the higher risk of resistant organisms and more severe systemic infection ¹.

CAP severity is often assessed using scores like CRB-65 or CURB-65, which incorporate confusion, respiratory rate, blood pressure, and age, guiding decisions on hospital admission and treatment intensity ¹,². These scores are less validated for HAP, where clinical judgment and knowledge of hospital flora guide management ¹.

Microbiologically, CAP is commonly caused by Streptococcus pneumoniae and atypical pathogens, whereas HAP is more frequently associated with multidrug-resistant organisms including Gram-negative bacilli and Staphylococcus aureus, reflecting the hospital environment and prior antibiotic exposure ¹. This difference influences empirical antibiotic choices and prognosis.

In summary, the key differentiators are the timing of pneumonia onset relative to hospital admission, the setting of acquisition, the likely pathogens involved, and the severity and complexity of the clinical presentation, with HAP generally occurring in more vulnerable patients with potentially more resistant infections ¹.