Given CMV IgG titer 1:128 and CMV IgM >1:10, with Toxoplasma IgG 1:128 and Toxoplasma IgM <1:10, what is the best interpretation?

Given CMV IgG titer 1:128 and CMV IgM >1:10, with Toxoplasma IgG 1:128 and Toxoplasma IgM <1:10, what is the best interpretation?

• A. Co-infection CMV and EBV
• B. Primary infection to toxoplasma
• C. Primary infection to CMV
• D. Primary infection to EBV

Answer: (D)

This pattern highlights how serology can be influenced by one infection creating antibody responses that mimic others. In EBV infection, there is broad polyclonal B‑cell activation that can produce nonspecific IgM antibodies. Those IgM antibodies can cross-react and yield a positive CMV IgM result even if CMV isn’t the active driver of illness. So a positive CMV IgM with a substantial CMV IgG titer doesn’t necessarily indicate an active CMV infection in this context. The toxoplasma result supports this: Toxoplasma IgG is present, but the IgM is not elevated, which is typical of a past exposure rather than a current toxoplasmosis infection. That makes acute toxoplasmosis unlikely. Taken together, the serology pattern is most consistent with a primary EBV infection, with the CMV IgM positivity likely representing a false-positive or non-specific result in the setting of EBV-driven polyclonal B-cell activation.

This pattern highlights how serology can be influenced by one infection creating antibody responses that mimic others. In EBV infection, there is broad polyclonal B‑cell activation that can produce nonspecific IgM antibodies. Those IgM antibodies can cross-react and yield a positive CMV IgM result even if CMV isn’t the active driver of illness. So a positive CMV IgM with a substantial CMV IgG titer doesn’t necessarily indicate an active CMV infection in this context.

The toxoplasma result supports this: Toxoplasma IgG is present, but the IgM is not elevated, which is typical of a past exposure rather than a current toxoplasmosis infection. That makes acute toxoplasmosis unlikely.

Taken together, the serology pattern is most consistent with a primary EBV infection, with the CMV IgM positivity likely representing a false-positive or non-specific result in the setting of EBV-driven polyclonal B-cell activation.