A 19-year-old man presents to clinic with recurrent jaundice and fatigue. Four weeks ago he developed jaundice, dark urine, and right upper quadrant discomfort after returning from a 5-month study-abroad program in Southeast Asia; those symptoms resolved completely within 2 weeks without treatment. He has no prior hepatitis vaccination and no known liver disease. Today his symptoms have returned in identical fashion. Scleral icterus is present and the liver is mildly enlarged. ALT is 340 U/L, total bilirubin is 3.8 mg/dL. Hepatitis panel: anti-HAV IgM positive, anti-HAV IgG positive, HBsAg negative, anti-HCV negative.
Which of the following best explains this patient's current presentation?