A patient presents with gradual onset of low-grade fever, marked fatigue, and severe sore throat. What condition is most likely?

The symptoms described in the scenario—gradual onset of low-grade fever, marked fatigue, and severe sore throat—are most indicative of infectious mononucleosis. This viral illness, often caused by the Epstein-Barr virus, is characterized by a triad of symptoms: fatigue, fever, and pharyngitis (sore throat). Patients may also experience lymphadenopathy, especially in the cervical region, and an increased number of atypical lymphocytes in the blood.

The gradual onset is a hallmark of mononucleosis, distinguishing it from other conditions that often present more acutely. While sore throat can be associated with conditions such as influenza and herpes zoster, the combination of profound fatigue and the type of sore throat usually seen in mononucleosis makes it the most likely diagnosis in this case.

In contrast, gonorrhea typically presents with purulent discharge and is less likely to cause systemic symptoms like severe fatigue and fever to the extent described. Influenza often has a sudden onset with more systemic symptoms, including body aches and significant respiratory involvement, which are not mentioned here. Herpes zoster is characterized by a painful, localized rash, which is not aligned with the symptoms presented in this scenario.