What distinguishes chemical pneumonitis from aspiration pneumonia?

• A. It is caused by bacterial infection
• B. It is an inflammatory reaction caused by aspiration of gastric fluid
• C. It is caused by viruses
• D. It resolves without any reaction

Answer: (B)

Chemical pneumonitis is a chemical injury to the lungs that occurs when gastric contents are aspirated, triggering an inflammatory reaction without necessarily involving a bacterial infection. The key idea is that the injury comes from the irritant properties of the aspirate—acid and digestive enzymes—rather than from microbes. This inflammatory process can lead to edema, damaged alveolar walls, and varying degrees of hypoxemia, often occurring soon after the aspiration event.

In contrast, aspiration pneumonia develops when the aspirated material includes bacteria from the oropharynx, leading to an infectious pneumonia with bacterial growth, fever, purulent sputum, and localized consolidation on imaging. Because bacteria are responsible, antibiotics are typically a mainstay of treatment for aspiration pneumonia, whereas chemical pneumonitis is managed with supportive care and monitoring for potential complications.

So, the distinguishing feature is that chemical pneumonitis is the inflammatory lung injury from chemical exposure due to aspiration, not an infection from bacteria.