Commonest cause of lung abscess is
**Core Concept**
Lung abscesses are a type of necrotizing pneumonia characterized by a localized collection of pus in the lung tissue. They often result from an infection that spreads from the airways to the lung parenchyma.
**Why the Correct Answer is Right**
The commonest cause of lung abscess is anaerobic bacterial infection, usually resulting from aspiration of oral or gastrointestinal contents. This occurs when bacteria, such as *Fusobacterium necrophorum* and *Peptostreptococcus magnus*, colonize the lung tissue and multiply in an anaerobic environment. The infection can also be facilitated by the presence of foreign material, such as food particles or dental plaque, which provides a nidus for bacterial growth.
**Why Each Wrong Option is Incorrect**
* **Option A:** Aspiration of sterile water or other non-bacterial substances is unlikely to cause a lung abscess, as it does not provide a source of infection.
* **Option B:** Viral infections, such as influenza or respiratory syncytial virus (RSV), can cause pneumonia but are not typically associated with lung abscess formation.
* **Option C:** Fungal infections, such as histoplasmosis or coccidioidomycosis, can cause pulmonary infections but are not the most common cause of lung abscess.
**Clinical Pearl / High-Yield Fact**
Aspiration of oral or gastrointestinal contents is a major risk factor for lung abscess formation, highlighting the importance of proper oral hygiene and dental care in patients with risk factors for aspiration.
**Correct Answer: D. Anaerobic bacterial infection**