A 68-year-old man with chronic obstructive pulmonary disease presents with productive cough, fever, and dyspnea. Chest X-ray shows patchy infiltrates in multiple lobes. Which is the most common causative organism in this clinical scenario of bronchopneumonia?

Explanation

## Most Common Cause of Bronchopneumonia **Key Point:** Haemophilus influenzae is the most common causative organism of bronchopneumonia, particularly in patients with underlying chronic lung disease such as COPD. ### Pathophysiology of Bronchopneumonia Bronchopneumonia is characterized by: - Patchy, multifocal consolidation (often bilateral) - Inflammation centered around small airways (bronchioles) - Aspiration of oropharyngeal secretions - Common in elderly and immunocompromised patients ### Organism Frequency in Bronchopneumonia | Organism | Frequency | Risk Factors | Pattern | |----------|-----------|--------------|----------| | **Haemophilus influenzae** | **Most common** | COPD, smoking, elderly | Multifocal, patchy | | Streptococcus pneumoniae | Second common | Alcoholism, splenectomy | Lobar (classic) | | Staphylococcus aureus | Less common | Post-influenza, IV drug use | Patchy, cavitation risk | | Klebsiella pneumoniae | Aspiration-prone | Alcoholism, aspiration | Lobar, cavitation | **High-Yield:** In COPD patients presenting with bronchopneumonia, *Haemophilus influenzae* (often non-typeable strains) is the most frequent isolate, followed by *Streptococcus pneumoniae*. ### Clinical Pearl **Clinical Pearl:** Haemophilus influenzae thrives in damaged airways with impaired mucociliary clearance — the hallmark of COPD. This organism colonizes the respiratory tract and ascends from the bronchioles during acute exacerbations. ### Distinction: Lobar vs Bronchopneumonia Organisms ```mermaid flowchart TD A[Pneumonia]:::outcome --> B{Pattern on CXR?}:::decision B -->|Lobar consolidation| C[Streptococcus pneumoniae]:::outcome B -->|Patchy, multifocal| D[Haemophilus influenzae]:::outcome C --> E[Aspiration risk: Klebsiella]:::outcome D --> F[COPD/chronic disease]:::outcome ``` **Mnemonic:** **HACEK** organisms are fastidious gram-negatives; **H. influenzae** is the most common respiratory pathogen in bronchopneumonia (especially COPD).