**Core Concept:** Pulmonary diseases can present with various symptoms and signs, including cough, fever, and radiographic abnormalities like infiltrates. Leukocytosis is a common finding in infections. Clinical presentation and imaging can help narrow down the differential diagnosis, but the most probable outcome still depends on the specific disease process.

**Why the Correct Answer is Right:**

The correct answer (D) is "afebrile" because the patient initially had fever, which is a classic sign of infection or inflammation. Her condition improved in a week, suggesting a self-limiting process like an acute respiratory infection. The presence of bilateral patchy infiltrates on chest radiograph further supports this diagnosis, as they are indicative of an acute pulmonary process resolving.

**Why Each Wrong Option is Incorrect:**

A. "Diffuse infiltrates" is not specific enough, as it is a broad description of radiographic findings and does not address the self-limiting nature of the disease.

B. "Pleural effusion" is an uncommon presentation in acute respiratory infections in elderly patients.

C. "Pulmonary tuberculosis" is an unlikely answer as it is typically associated with systemic symptoms and constitutional signs, which were not present in this case.

**Why Each Wrong Option is Incorrect:**

A. "Pulmonary fibrosis" presents with chronic symptoms and signs and does not resolve within a week.

B. "Pulmonary tuberculosis" often presents with systemic symptoms and constitutional signs, which were not present in this case.

**Why Each Wrong Option is Incorrect:**

C. "Pulmonary embolism" typically presents with hemoptysis, chest pain, and dyspnea. It also presents with abnormal lung sounds on auscultation, which were not mentioned in the case.

**Clinical Pearl:**

In cases of acute respiratory infections in elderly patients, the presence of bilateral infiltrates, improvement over time, and lack of systemic symptoms and signs should raise suspicion for an acute respiratory infection. The correct answer is based on the clinical improvement and the specific radiographic findings.