1. Presented by Seena Tabibi MD
Reviewed by Karen Carroll MD

An adult patient presented to the Emergency Department with fever, watery diarrhea, confusion, headache, dry cough, and generalized weakness. The symptoms began three days prior to presentation. Past medical history is significant for extensive tobacco use. However, the patient recently quit smoking several weeks prior to presentation. The patient has not had any recent hospitalizations and does not have any sick contacts. On presentation vital signs are as follows:

Temperature 39.4° Celsius
Respirations: 18/minute
Heart Rate: 86 beats/minute
Pulse Oximetry: 94%
Blood Pressure: 114/74 mmHg

Physical Examination revealed decreased breath sounds in the right lower lobe with mild nonspecific tenderness to palpation over the abdomen. The heart rhythm was regular. No other abnormalities were noted.

Chest X-ray revealed right-sided peri-hilar infiltrates with no evidence of pleural effusion or pneumothorax. Computed Tomography supported the chest X-ray findings by demonstrating right lower lobe consolidation.

Laboratory Studies are as follows:

White Blood Cell Count: 14.53 K/cu mm (Reference 4.50-11.00 K/cu mm)
Absolute neutrophil count: 12.64 K/cu mm (Reference: 4.50-11.00 K/cu mm)
Pro-calcitonin: 6.42 ng/mL (Reference: less than 0.10 ng/mL)
Sodium: 137 meq/L (Reference: 135-148 meq/L)
Creatinine: 1.6 mg/dL (Reference: 0.5-1.4 mg/dL)
C-reactive protein: 24.0 mg/dL (Reference: 0.0-0.5 mg/dL)

Which of the following is the most likely diagnosis?