Review Question - QID 213175

A 29-year-old woman comes to the clinic complaining of headache and cough for the past 3 days. She thought that she had a common cold, but she is feeling progressively worse and decided to come to the emergency room today. She reports a nonproductive cough, sore throat, rhinorrhea, and shortness of breath but denies fever, chills, chest pain, or abdominal pain. Her past medical history is significant for asthma that is well controlled with albuterol. A physical examination demonstrates mild tenderness of the right lower chest upon palpation and mild rales and wheezes in the bibasilar lung fields. A chest radiograph is obtained and its results are shown in Figure A. Laboratory studies are shown below:

Hemoglobin: 9.1 g/dL
Hematocrit: 27%
Leukocyte count: 7,400/mm^3 with normal differential
Platelet count: 160,000/mm^3

Serum:
Na+: 137 mEq/L
Cl-: 97 mEq/L
K+: 3.8 mEq/L
HCO3-: 25 mEq/L 
BUN: 8 mg/dL 
Glucose: 117 mg/dL
Creatinine: 0.4 mg/dL
Thyroid-stimulating hormone: 4.1 µU/mL
Ca2+: 9.2 mg/dL
AST: 16 U/L
ALT: 15 U/L

What is the most likely explanation of this patient’s presentation?