YBX3 and infectious mononucleosis: However, a significant disadvantage to the Vidas IgG test is that it also gave LD-positive status to 53% (8/15) of the subjects in the mononucleosis group and 87% (13/15) of the subjects in the syphilis group, compared to 7% (1/15) and 0% (0/15), respectively, for the DbpA/C6-OspC test.