(P396) Evaluation of the Chembio DPP® HIV-Syphilis Point-of-care Assay for Syphilis Screening in Clinical Settings

Background: Point-of-care (POC) syphilis tests have the potential to expedite treatment and prevent onward transmission. We evaluated the performance and impact of the syphilis component of the Chembio DPP® HIV-Syphilis System (POC test).

Methods: Participants were enrolled at a sexual health clinic and HIV clinic in Seattle, WA, and an emergency department and a research clinic in Baltimore, MD. All participants were tested for antibodies against HIV and Treponema pallidum (TP) with the POC test using unprocessed venipuncture EDTA whole blood. Participants in Seattle were also tested with a qualitative rapid plasma reagin (RPR) that reflexed to RPR titer and TP-enzyme immunoassay (EIA) if reactive and a TP-particle agglutination test (TPPA) if RPR/TP-EIA were discordant or if ordered by a provider. Participants in Baltimore were tested with Liaison TP-EIA that reflexed to RPR and titer if reactive and TPPA when EIA/RPR were discordant. Prior syphilis diagnosis was ascertained from participant report or medical record review. Syphilis staging was determined by health department staff and communicated to study teams.

Results: From August 2021-November 2022, 699 participants received a POC test and 23% (163/699) were POC reactive for syphilis. Of 163 reactive results, 22 (13%) represented active infection (i.e., requiring treatment; 2 primary, 5 secondary, 8 early latent, 7 late latent/unknown duration), 125 (77%) prior syphilis diagnosis, and 16 (10%) were false-reactive. POC test sensitivity for active syphilis was 100%. Of 159 participants with a history of syphilis (23% of all participants), 135 (85%) had reactive POC tests, including all 10 participants with active infection. Positive predictive value (PPV) for active syphilis was 7% (10/135) among those with a syphilis history and 36% (9/25) among those with no prior infection. A greater proportion of people with HIV than those without HIV tested DPP TP-reactive (39% [47/119] vs 20% [116/580]).

Conclusions: In populations with a high prevalence of syphilis infection, the POC test identified all new syphilis infections. However, the majority of reactive tests indicated a prior diagnosis. PPV for infections requiring treatment was low, but assessing history of prior syphilis infection can be useful for interpreting reactive tests.