Large diagnostic panels allow for pathogens with high or low likelihood of causing attributable illness to be tested simultaneously. Infectious mononucleosis (IM) due to primary infection with Epstein-Barr virus (EBV) is a common cause of acute febrile illness (AFI) in case series from high-income countries, though its contribution to AFI in tropical low-income settings is unclear. As part of a case-control study using multiplex quantitative polymerase chain reaction (qPCR) diagnostics, we set out to determine if primary EBV infection was an underrecognized cause of AFI in the Peruvian Amazon. Presence of EBV DNA in whole-blood samples was equally prevalent among febrile cases and afebrile controls (34.6% [247/714] versus 35.7% [248/695]) and was not correlated with classic IM symptoms. Given the clear lack of clinical significance of the whole-blood PCR results, additional testing was pursued to ascertain the true prevalence of IM among cases of AFI in this population. The presence of EBV DNA in plasma, a marker of active EBV-related processes, was detected in 7% (5/68). Anti-EBNA-1 IgG, a late marker of prior infection, was tested via ELISA and detected in 4/5 of the plasma-positive patients, thereby excluding an acute primary EBV infection in all but one patient. Infectious mononucleosis due to primary infection with EBV was not an important etiology of AFI in the Peruvian Amazon, despite high rates of initial test positivity.