A 9-week pregnant woman is found to be CMV IgG positive and IgM positive. She recalls no prior illness. Which result would most reliably exclude a recent primary CMV infection?

• A Isolated IgG positivity on repeat testing after 2 weeks
• B Positive CMV DNA PCR on maternal saliva
• C Low CMV IgG avidity index
• D High CMV IgG avidity index ✓

Explanation

IgG avidity matures over the months following primary infection, so a high avidity index indicates infection acquired at least 3 to 4 months earlier and effectively rules out primary infection acquired during the current pregnancy. Low avidity suggests recent primary infection but can persist for months and is less definitive. Maternal saliva PCR is not a standard test here, and isolated stable IgG without IgM would suggest past infection but the scenario already shows IgM positivity.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.