Background:
Syphilis staging helps to determine appropriate public health follow-up for patients and partners. Use of a cut-off value from the rapid plasma reagin (RPR) titer has been proposed as an alternative to determine follow-up priority among patients with latent syphilis.

Objective:
To compare syphilis titers to current syphilis stage definitions.

Method:
We describe RPR titers for syphilis cases reported between 1997 and 1999 in Columbia South Carolina, Houston Texas, and Jackson Mississippi. Using the sensitivities and specificities of various titer cutoff values we generated a receiver-operating curve (ROC) to evaluate the predictive value for early latent syphilis compared to the current definition.

Result:
For primary syphilis, the modal titer was 1:16, with a range of 1:1-1:8192; for secondary, the mode and range were 1:128 and 1:1-1:4096, for early latent 1:64 and 1:1-8192, and for late latent 1:16 and 1:1-1:2046. Compared with the current definition of early latent syphilis, a titer cutoff value of 1:32 had sensitivity of 64% and specificity of 74% for classifying early latent cases according to the current definition.

Conclusion:
While titer could be used to determine priority of follow-up for cases of latent syphilis, classification of early syphilis would change for up to 25% of cases currently classified as early latent.


Implications:
If priority for follow up of latent syphilis cases is determined by titer, roughly but not exactly the same population will be considered high priority for follow-up as is determined by current classification. The effect on partner services is not known.