One winter afternoon, Matthew, a 30-year-old clerk with an unremarkable past medical history, presents with symptoms of generalized malaise, weakness with dry cough and increasing dyspnea. He's been suffering from flu-like symptoms such as aches and pains, fever and muscle cramps over the past 10 days. In fact, he went to the emergency department 5 days ago but was sent home with the assurance that he only had a viral syndrome. The following day, he noted discolouration of his urine to dark orange. His appetite has been poor for a week but he denies any nausea, vomiting or diarrhea. He also doesn't have abdominal or chest pain, nor does he declare any joint pain, skin rash or hair loss.

Further inquiry reveals that his son recently had the chicken pox and that they had their furnace cleaned 3 weeks prior to the onset of symptoms. They also got a cat and a dog in the past 3 months. Matthew isn't on any medications and he doesn't smoke. While he drinks socially, he denies any drug use.

Physical examination reveals a listless young man with icterus. He's afebrile and cervical and axillary lymph nodes are normal. On chest exam, you find a resonant chest with fair air entry bilaterally and few crackles at the right lung base. Heart sounds are normal without any murmurs or added sounds. Abdominal examination is unremarkable and non-tender; there's no hepatomegaly or splenomegaly. There's also no pedal edema. Neurologic exam is non-focal.

A urinalysis shows a pH of 6.0, specific gravity of 1.015, 1+ protein, 1+ blood, 2+ bilirubin, 4+ urobilinogen and 0-5 WBC/HPF. Chest x-ray reveals bilateral interstitial infiltrate, more prominent in the right lower lung. An urgent abdominal ultrasound the next morning is unremarkable, however. Specifically, there's no evidence of hepatobiliary pathology. Hemoglobin has dropped to 67 g/L. What's your diagnosis?