Q. A 7-year-old boy is brought to the pediatric clinic by his parents with a 5-day history of fever, fatigue, and malaise. His parents mention that, unlike previous respiratory infections, he has not developed a cough this time. On examination, the child appears lethargic but is not in respiratory distress. His temperature is 38.5°C (101.3°F). Auscultation of the lungs reveals diffuse crackles but no wheezing. A chest X-ray is performed and shows interstitial infiltrates. Blood tests indicate a normal white blood cell count with a slight increase in lymphocytes. Based on the clinical presentation, a particular microorganism is suspected. Which microorganism is most likely responsible for the atypical pneumonia in this child?