False Positive Immunoglobulin M Antibody to Cytomegalovirus in Child with Infectious Mononucleosis Caused by Epstein-Barr Virus Infection

Infectious mononucleosis (IM) results from Epstein-Barr virus (EBV) and IM-like syndromes, mainly due to cytomegalovirus (CMV), Toxoplasma gondii or human immunodeficiency virus (HIV). EBV and CMV infection are common in humans. In immunocompetent persons, these infections are usually asympto-matic, however, can manifest as a severe infection in immunocompromised persons. The hallmarks of IM are fever, pharyngitis, lymphadenopathy, and a mononuclear cell count (lymphomonocytosis); ≥ 50 % of the white blood cells (WBC) with atypical or reactive morphology of the lymphocytes in the peripheral blood.1,2 Additional features include splenomegaly or exanthema, and may contribute to the clinical diagnosis. We present a 16-month-old boy who had severe hepato-megaly which was detected incidentally during the admission period and was shown to have dual positive Immunoglobulin (Ig) M antibody to CMV and EBV. Initially, we thought that the patient had co-infection of CMV and EBV, however, after 1 year of follow-up, transient increase in CMV IgM was followed by persistent absence of CMV IgG and confirmation of EBV infection by serocon-version of IgG Epstein-Barr nuclear antigen (EBNA), suggesting that the CMV IgM test was false positive