Imported from Cuba?

A 21-year-old man presented to the emergency room complaining of fever, chills, diarrhea and nausea with vomiting of two days' duration. He had a past medical history of remote jejunal dysplasia, which was surgically corrected when he was a child. He was taking no regular medications. He had been well until two days earlier, when he developed a sudden onset of fever to 39.9°C, chills and severe nausea with frequent bouts of vomiting. He remembered feeling more tired than usual for three days before the onset of his fever, but nothing more specific. He saw a physician the day after the onset of fever, and the physician prescribed oral cotrimoxazole double-strength, of which he took one dose. Due to persistence of the above symptoms, he presented to the emergency room. He had travelled to Cuba for a seven-day vacation at a resort, and returned home 14 days before the onset of symptoms. He had experienced one day of mild diarrhea while in Cuba, but two of his friends experienced two to three days of diarrhea without fever at the same time while there. He denied abdominal pain, headache, cough, shortness of breath, rash, urinary symptoms or other problems. He had no risk factors for HIV infection. On examination, he was toxic and experiencing rigors, but was awake and alert. His temperature was 39.8°C, pulse was 107 beats/min and respirations were 30 breaths/min. The examination was normal except for evidence of dehydration and marked splenomegaly without tenderness. A chest radiograph and urinalysis were normal. The patient's hemoglobin level was 167 g/L, his platelet count was 138x10/L and his leukocyte count was 9.5x10/L with a marked shift to the left. The patient's creatinine level was 139 μmol/L, urea level was 6.8 mmol/L, total bilirubin level was 48 μmol/L (44% conjugated), alanine aminotransferase level was 113 U/L and gamma glutamyl transpeptidase level was 83 U/L. Other liver function tests were normal. Blood and urine cultures were obtained. An abdominal ultrasound confirmed the presence of splenomegaly with a tiny splenic cyst and an otherwise normal examination (including a normal liver). Infectious enteritis with sepsis was diagnosed and the patient was started on intravenous ciprofloxacin. The following day, two sets of blood cultures that were taken while the patient was in the emergency room showed the presence of Gram-negative rods, which were identified the next day as species (serogroup C1), susceptible to ampicillin, cotrimoxazole, fluoroquinolones and ceftriaxone. After three days of taking parenteral ciprofloxacin, the patient felt subjectively better but continued to have afternoon and evening fevers of more than 40°C, accompanied by rigors and extreme exhaustion. His platelets decreased daily, to a nadir of 49x10/L, and his leukocytes decreased to 3.8x10/L. HIV serology was negative. He had no other new complaints, and the examination was unchanged. Repeat blood cultures were negative. A diagnostic procedure was performed to explain the persistent sepsis. What is your diagnosis?