Missed opportunities to diagnose occult primary syphilis among adults from sti clinics in peru

Background Primary syphilis, the most contagious disease stage, is when serologic tests are most likely to be negative. Including the anal canal in the clinical exam can aid diagnosis, especially during this period. We used preliminary data from our PICASSO cohort to discuss the probability of occult primary syphilis in adults not presenting with cutaneous or oral lesions. Methodology Occult primary syphilis probability (OPSP) was classified into three categories (Gunn, 2019): 1. High, having a non-reactive RPR/TP-rapid test (TP-RT) within one year; 2. Intermediate, having a non-reactive RPR/TP-RT more than a year ago; and 3. Low, no prior non-reactive RPR/TP-RT. The higher the probability of occult primary syphilis, the higher the potential benefit from an anal exam. Participants were eligible for OPSP classification if they had a diagnosis of asymptomatic (latent) syphilis, recent condomless receptive anal sex, and current RPR result ≤1:8 if HIV-negative and first TP infection, or RPR result ≤1:128 if HIV positive and/or had prior syphilis. Results Forty-eight participants were eligible for OPSP classification. Among those, 19 (40%) were HIV positive, 35 (73%) had prior syphilis, and 42 (88%) were diagnosed with early latent syphilis. Twenty participants (42%) were classified as high OPSP, 3 (6%) as intermediate, and 25 (52%) as low OPSP. Anoscopes were available at the study centers for 19 of the 48 cases, but only one anoscopy (5%) was performed. No anal lesions were found despite 13/19 (68%) being classified as high OPSP. Participant refusal was the primary reported reason for lack of anoscopy. Conclusion High OPSP among asymptomatic individuals with primary syphilis is common, but anoscopy was used infrequently even when available, missing the opportunity of diagnosis. Anoscopy promotion among clinicians and patients is needed to reduce the gap of under-diagnosed primary syphilis and prevent TP transmission when it is most contagious.