A child has mononucleosis-like symptoms yet the test for mononucleosis and the EBV titers are negative. One of the causes of heterophile-negative mononucleosis is

Infectious mononucleosis caused by cytomegalovirus (CMV) is clinically difficult to distinguish from that caused by Epstein-Barr virus. Lymphocytosis is usually present with an abundance of atypical lymphocytes. CMV-induced mononucleosis should be considered in any case of mononucleosis that is heterophil-negative and in patients with fever of unknown origin.