Final answer:
The most likely diagnosis for the 45-year-old man with fever, chills, anorexia, diarrhea, and a non-productive cough is Legionnaire's disease.
Step-by-step explanation:
The most likely diagnosis for the 45-year-old man with fever, chills, anorexia, diarrhea, and a non-productive cough, along with patchy alveolar infiltrates with consolidation in the lower lobe on chest X-ray, is Legionnaire's disease. Legionnaire's disease is caused by the bacterium Legionella pneumophila and is typically acquired through inhalation of contaminated water droplets. Symptoms of Legionnaire's disease include high fever, cough, and shortness of breath. Treatment involves antibiotics such as levofloxacin or azithromycin.