Bacterial pneumonia, characterized by inflammation in lung parenchyma and alveolar spaces, is caused by various bacteria, each triggering an intricate interplay with the host immune response. Clinically, patients may experience symptoms such as fever, cough, dyspnea, and chest pain, with potential complications ranging from necrotizing pneumonia and empyema to meningitis, sepsis, and multiple organ failure. Long-term impacts on pulmonary function and quality of life can ensue.

The word pneumonia is rooted in the ancient Greek word pneumon ("lung"). Therefore, pneumonia can be understood as "lung disease." Clinically, it manifests as an inflammation of the parenchyma and alveolar spaces in 1 or both lungs, primarily attributed to infections, though not exclusively.

Among the infectious causes of pneumonia, bacteria, viruses, fungi, and parasites are prominent. Bacterial pneumonia has a significant impact on the overall morbidity and mortality rates of those with pneumonia. Various classification methods exist for organizing pneumonia, with the National Institutes of Health (NIH) system being the most widely embraced. This system categorizes pneumonia into community-acquired, hospital-acquired, and atypical pneumonia, further stratified based on severity.

Additional classifications may include healthcare-acquired pneumonia (HCAP), which encompasses pneumonia acquired in hospitals, dialysis units, residential aged facilities, and ventilator-associated pneumonia (VAP). However, HCAP has been omitted from American guidelines due to a lack of evidence regarding microbiological differences between community-acquired pneumonia (CAP) and HCAP.

Bacterial Pneumonia Definitions

1. Community-acquired pneumonia: CAP is the acute infection of lung tissue occurring in a patient who has acquired it from the community or within 48 hours of hospital admission.

1. Hospital-acquired pneumonia: HAP is an acute infection of lung tissue in a nonintubated patient that develops after 48 hours of hospitalization.

1. Atypical pneumonia: The acute infection caused by a pathogen not detectable by traditional Gram stain or standard cultures.

1. Ventilator-associated pneumonia: VAP is a type of nosocomial infection of lung tissue that usually develops 48 hours or longer after intubation for mechanical ventilation.