**Core Concept**
The patient's presentation of febrile neutropenia and subsequent development of bilateral fluffy infiltrates on chest X-ray is suggestive of ventilator-associated pneumonia (VAP) or possibly a more severe condition such as acute respiratory distress syndrome (ARDS). This scenario requires prompt recognition and management to prevent further complications.

**Why the Correct Answer is Right**
In a patient with febrile neutropenia, the development of new lung infiltrates raises concerns for an opportunistic infection, particularly in the context of broad-spectrum antibiotic use. The fluffy infiltrates on chest X-ray are indicative of an alveolar process, potentially due to an infection. The most appropriate next step is to obtain a sample for microbiological analysis, such as a bronchoalveolar lavage (BAL) or a protected specimen brush (PSB), to guide targeted antibiotic therapy. This approach helps to avoid unnecessary broad-spectrum antibiotic use and reduces the risk of antibiotic resistance development.

**Why Each Wrong Option is Incorrect**
**Option A:** Administering antifungal therapy would be premature without microbiological evidence of a fungal infection. Fungal infections are a concern in immunocompromised patients, but the presence of fluffy infiltrates is more suggestive of a bacterial or viral etiology.

**Option B:** Initiating corticosteroids would be inappropriate in this scenario, as there is no clear indication for their use. Corticosteroids are used to modulate the immune response, but they are not the first line of treatment for suspected VAP or ARDS.

**Option C:** Repeating the chest X-ray may provide additional information, but it does not address the need for microbiological analysis to guide targeted antibiotic therapy.

**Option D:** Discontinuing broad-spectrum antibiotics would be inappropriate, as the patient is still at risk for an opportunistic infection. However, the use of broad-spectrum antibiotics should be reassessed based on the microbiological results.

**Clinical Pearl / High-Yield Fact**
In critically ill patients, the development of new lung infiltrates requires prompt recognition and management. A high index of suspicion for ventilator-associated pneumonia or acute respiratory distress syndrome is essential, and targeted antibiotic therapy should be guided by microbiological analysis.

**Correct Answer:** .