CROI 2024 Abstract eBook

Abstract eBook

Poster Abstracts

abundance was normalized per million reads sequenced (reads per million, rpm); ARG abundance and expression were additionally normalized by gene length (depth per million, dpm). P-values were obtained by the Wilcoxon rank-sum test and adjusted for multiple comparisons. Linear regression tested the association between number of DP doses taken since enrollment to TCN ARG expression. Results: Gut bacterial microbiome alpha diversity, beta diversity, and total bacterial abundance did not differ between SOC and DP arms at M0 or M6, or over time by arm. TCN ARGs were detected in all M0 DNA-seq samples, with 46% of all ARG abundance derived from TCN ARGs. Median TCN ARG expression increased 4.4-fold between M0 and M6 in the DP group (0.07 to 0.31 dpm; p<0.01) and was 5-fold higher at M6 in the DP versus SOC group (0.31 versus 0.06 dpm; p<0.01; Figure). There were no significant differences in ARG expression between M0 and M6 DP samples for non-TCN class ARGs. DP participants with M6 RNA-seq samples took a median of 42 DP doses between M0 and M6 (IQR: 29-65 doses), and we found that a higher number of DP doses was associated with greater TCN ARG expression (p<0.01). Conclusion: Doxy-PEP did not significantly alter bacterial gut microbiome diversity or composition but was associated with an increase in TCN ARG expression, without affecting non-TCN ARG classes. The clinical impact of these findings remains undetermined and should be further studied.

diagnosis history, HIV PrEP use, and sexual behavior. We used chi-square tests to compare characteristics of STI prophylaxis users and non-users. Results: As of 27 September 2023, 649 respondents in 50 states, DC, and Puerto Rico had completed the survey. Most (89%) were GBM, and 42% were HIV PrEP users, 19% living with HIV, 59% White, 23% Black, and 13% Latinx. Overall, 95% were interested in using STI prophylaxis; 49% had previously heard of it, and 22% and 16% had used it ever or in the past 12m, respectively. Of the 143 respondents with any STI prophylaxis use, 45% had used it before sex and 72% after sex; of those who used it after sex, 45% had taken it within 24h. Those with STI prophylaxis use in the past 12m used it for some (47%), most (32%), or all (21%) sex acts with casual partners. Medications used as STI prophylaxis included doxycycline (78%), amoxicillin (19%), and azithromycin (16%), and medication sources included leftover from treatment of a past STI (11%) or other condition (20%) and bought online without a prescription (12%). Compared to non-users, STI prophylaxis users were younger (mean age 39 vs 43, P=0.007) and a higher proportion were HIV PrEP users (56% vs 38%, P<0.001), reported >10 partners (61% vs 31%, P<0.001) or group sex (74% vs 49%, P<0.001) in the past 12m, and ever had an STI (75% vs 47%, P<0.001). Reasons for interest/use and concerns about use varied (Figure). For doxyPEP specifically, 36% had heard of it and 13% had used it in the past 12m, of whom 24% had used a dosage other than the 200mg dose shown to be effective. Conclusion: Interest in STI prophylaxis is nearly universal and use is already common among GBM engaged in online networks. Some are using medications and dosing that are untested as STI prophylaxis. Findings can inform doxyPEP implementation strategies, including education on effective dosing and monitoring of actual use.

Poster Abstracts

1155 WITHDRAWN Increase in Syphilis Cases Diagnosed at a Tertiary IHS Facility Following Expanded Screening

Voichita Ianas , Heather Huentelman Phoenix Indian Medical Center, Phoenix, AZ, USA

Background: American Indians and Alaska Natives (AI/AN) have the highest rates of reported cases of primary, secondary, and congenital syphilis of any race/ ethnicity in the United States as of 2021. The Phoenix Indian Medical Center (PIMC) is a tertiary, Indian Health Service facility located in Arizona. PIMC serves of over 156,000 AI/AN annually. In 2023, PIMC implemented facility-wide syphilis screening. Methods: Phoenix Indian Medical Center medical records were pulled for syphilis patients diagnosed during January-June 2022 and January – June 2023. Case characteristics, syphilis staging, and clinical service of diagnosis were evaluated. Results: PIMC had 23% increase in syphilis cases when comparing January June 2022 (n=127) to the same time period in 2023 (n=156). In first 6 months of 2023, 10.3% (n=16) of the cases were symptomatic classified as primary or secondary stage, while 89.7% were asymptomatic with 23.7% early latent and 66% late latent (early + late n = 140). 59% and 41% were birth gender male and female respectively; 31% of females at birth (20 females) were within childbearing age (15-49). Of childbearing age cases 20% were symptomatic (primary & secondary) (n = 4) and 80% (N=16) were asymptomatic. Syphilis cases were identified in 5 PIMC departments including urgent care/emergency services (28%), HIV treatment and prevention outpatient clinic (25%), primary care (29%), inpatient (10%) and women's clinic (8%). Only 42% of the cases identified were empaneled patients with a primary care provider. 15% of cases occurred in persons living with HIV (n = 23) and 10% were in persons on HIV prevention (PrEP) (n = 16). Conclusion: The increase in overall and asymptomatic syphilis case identification demonstrates the success in case finding through PIMC syphilis screening and diagnosis efforts and the need for more informed syphilis staging practices to optimize use of limited benzathine penicillin reserves during this period of high case diagnoses.

1154 Impact of Doxycycline as STI PEP on the Gut Microbiome and Antimicrobial Resistance Gene Expression

Victoria T Chu 1 , Abigail Glascock 2 , Deborah Donnell 3 , Cole Grabow 4 , Ryan Ward 1 , Christina Love 1 , Stephanie E. Cohen 5 , Julia C. Dombrowski 4 , Chase Cannon 4 , Michael Woodworth 6 , Colleen Kelley 7 , Connie Celum 4 , Annie Luetkemeyer 1 , Charles Langelier 1 1 University of California San Francisco, San Francisco, CA, USA, 2 Chan Zuckerberg Biohub, San Francisco, CA, USA, 3 Fred Hutchinson Cancer Center, Seattle, WA, USA, 4 University of Washington, Seattle, WA, USA, 5 San Francisco Department of Public Health, San Francisco, CA, USA, 6 Emory University, Atlanta, GA, USA, 7 Emory Center for AIDS Research, Atlanta, GA, USA Background: Doxycycline post-exposure prophylaxis (doxy-PEP) reduces bacterial sexually transmitted infections in men who have sex with men (MSM) and transwomen (TW) living with HIV or on HIV pre-exposure prophylaxis (PrEP). The impact on the gut bacterial microbiome and its associated antimicrobial resistance genes (ARGs) is unknown. Methods: The DoxyPEP trial compared doxy-PEP use (DP) to standard of care (SOC) for 501 MSM/TW living with HIV or on PrEP. Metagenomic sequencing of DNA and RNA (DNA-seq, RNA-seq) was performed on self-collected rectal swabs from enrollment (M0) and month 6 (M6) from 50 SOC and 100 DP participants matched by HIV infection status. We analyzed all samples passing minimum sequencing quality control standards. From DNA-seq data, we compared bacterial microbiome diversity and total bacterial abundance in 59 DP and 30 SOC participants, and assessed baseline tetracycline (TCN) ARG abundance at enrollment. We then compared changes in ARG expression at M0 and M6 using RNA-seq data of samples from 46 DP and 24 SOC participants. Bacterial

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