A febrile 23-year-old college student presents with fatigue and difficulty swallowing. Physical exam reveals exudative tonsillitis, palatal petechiae, cervical lymphadenopathy, and tender hepatosplenomegaly. A complete blood count reveals mild anemia, lymphocytosis with about 30% of the lymphocytes exhibiting atypical features, and a mild thrombocytopenia. Coombs' test is positive. Which of the following is the most likely complication of this syndrome?

The syndrome represented by the clinical vignette is infectious mononucleosis. Epstein-Barr virus (EBV) is the usual cause of heterophile-positive infectious mononucleosis; cytomegalovirus is responsible for a minority of cases. Rarely, splenic rupture requiring splenectomy can result from splenomegaly and capsular swelling, usually occurring during the 2nd and 3rd weeks of the illness. Acute cholecystitis is not associated with infectious mononucleosis. The most frequently isolated pathogens are E. coli, Klebsiella spp., group D Streptococcus, Staphylococcus spp., and Clostridium spp. Ascending cholangitis is not associated with infectious mononucleosis. Cholangitis usually presents with biliary colic, jaundice, and spiking fever with chills (Charcot's triad). Blood cultures are usually positive (E. coli is a common isolate), with an accompanying leukocytosis. AIDS-related cholangitis has been repoed, presenting with abdominal pain and obstructive liver symptoms. Potential etiologic agents include Cytomegalovirus, Cryptosporidium parvum, and Microsporidia, including Enterocytozoon cuniculi. Diarrhea is not usually produced by infectious mononucleosis.