Maximizing Case Finding Efforts Among Early Syphilis Contacts in An Era of Limited Field Investigation Resources

Background: Early syphilis morbidity has increased in California since 1999; however, local health department resources to respond effectively have concurrently decreased.  Optimization of currently available syphilis control resources is urgently needed.

Objectives: Evaluate syphilis case finding efforts by comparing three disease investigation strategies to inform program modification for maximizing field investigation resources.

Methods: Interviews of early syphilis cases diagnosed in the California Project Area (CPA) between 2007 and 2008 were assessed for newly identified/infected partners:  (1)   by comparing phone versus in-person original interviews; (2) from case re-interviews; and (3) from early latent cases, by months from the partner’s last sexual exposure to the original patient (OP).  Partner yield was measured using “partner index”:  number of newly identified/infected partners divided by number of cases interviewed.

Results: 3,344 early syphilis cases were diagnosed in the CPA from January 1, 2007 through December 31, 2008; 86% were interviewed.  In-person interviews yielded more newly infected partners (1,637 interviews, 207 new infections, index=.13) than did phone interviews (1,235 interviews, 74 new infections, index=0.06).  Of cases interviewed, 721 (25%) were re-interviewed.  90% of re-interviews yielded no additional partners; of the remaining 10%, 187 partners with 11 new infections were identified (index=.02).  Among 1,189 early latent cases, more new infections were identified among partners last exposed to the OP within 0-3 months before OP interview (71 new infections, index=.17), compared to partners exposed within 3-6 months (14 new infections, index=.11) or 6-12 months (4 new infections, index=.07).  

Conclusions: Field investigation resources can be more effectively used to increase partner yield and identify new infections when focused on in-person interviews and partners with recent sexual exposure to early latent cases. 

Implications for Programs, Policy, and/or Research: California is revising partner follow-up procedures based on these findings.  Health departments should use local data to evaluate program modifications, such as limiting re-interview efforts and/or focusing on in-person interviews.