(P401) HIV infection modifies the association between prior Treponema Pallidum infection and clinical presentation of early syphilis among patients from STI clinics in Peru

Background: The role of prior Treponema Pallidum (TP) infection on the clinical presentation of early syphilis may be different when comparing people by HIV status. We aim to evaluate the association of prior TP infection on clinical presentation of early syphilis stratified by HIV status; additionally, we explored the association of prior TP infection on lesion manifestations.

Methods: We used data from the baseline and four-week visits from the PICASSO cohort conducted in Peruvian STI clinics from 2019-2022. We included patients diagnosed with early syphilis by serology (current RPR ≥1:8 and 2-fold increase from previous RPR) and/or clinical exam (lesion compatible with syphilis), who also had previous RPR and/or TP rapid tests (TPrt) results to determine prior TP infection. Prior TP infection status was categorized as reinfection (previous RPR ≥1:8 or positive TPrt) or first infection (negative TPrt within 12 months). HIV status was determined by HIV rapid testing at enrolment. Logistic regression models were used to calculate adjusted prevalence ratios (aPR) of clinical presentation by prior TP infection status, stratified by HIV status (see Table 1 footnote on included variables). Primary and secondary lesions were each compared by prior TP infection status using Fisher’s exact tests.

Results: We included 145 cis-gender men and transgender women. TP first infection was positively associated with symptomatic (primary/secondary syphilis) clinical presentation at diagnosis (unadjusted PR=1.94; p=0.014). When stratified by HIV status, this association was significant among HIV-uninfected individuals (aPR=6.63; p=0.001), but not among those living with HIV (aPR=1.38; p=0.458) (See Table 1). Regarding lesion manifestations, among secondary syphilis cases (n=16), all cases with TP re-infection improved within one week, while only 29% of first TP exposure cases improved in this timeframe (p=0.045). Among primary syphilis cases (n=25), all lesions improved within one week. No differences were found by body distribution, pain or lesion number in primary or secondary syphilis cases.

Conclusion: The association between symptomatic early syphilis presentation and first TP exposure is more pronounced among patients without HIV. Furthermore, prior TP infection was associated with faster-perceived healing of secondary lesions. Our findings indicate the complexity of the host immune response to TP infection.