The prozone phenomenon with syphilis and HIV-1 co-infection.

The prozone phenomenon in syphilis testing refers to a false negative response resulting from overwhelming antibody titers which interfere with the proper formation of the antigen-antibody lattice network necessary to visualize a positive flocculation test. This prozone effect in syphilis testing can be expected in cases of disproportionately high antibody titers, such as secondary syphilis, or with human immunodeficiency virus (HIV) coinfection. Clinicians need to remain familiar with the protean manifestations of syphilis to be able to exclude the prozone phenomenon.