Chlamydia trachomatis and Neisseria gonorrhoeae bacterial loads in co-infected men who have sex with men on pre-exposure prophylaxis: a cross-sectional study

Objective

Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) are the most commonly reported sexually transmitted infections globally. Anorectal CT/NG detection among men who have sex with men (MSM) and co-infections are common. Epidemiological studies suggest that CT/NG co-infections might result in greater bacterial load and transmissibility than single infection. The purpose of this study was to compare bacterial load and symptoms between CT/NG single and co-infections in MSM.

Methods

MSM positive for CT or NG on a triple swab (throat, urethra, and rectal locations combined) were enrolled. Before treatment, they self-collected anorectal swabs. Bacterial loads for CT/NG were calculated using real-time PCR, and compared between single or co-infected individuals, and with or without rectal symptoms.

Results

We enrolled 382 MSM from December 2021 to December 2024. Among all samples: total CT (n=114), CT/NG co-infection 29/114 (25.4%); total NG (n=125), CT/NG co-infection 29/125 (23.2%). The bacterial loads in single and co-infected samples were comparable. The mean difference between CT alone and CT/NG was 0.40 copies/mL (95% CI: [-0.09, 0.11], P value = 0.107). The mean difference for NG alone and CT/NG was 0.24 copies/mL (95% CI: [- 0.49, 0.99], P value = 0.498). Among 382 MSM, 15.4% (n=59/382) experienced anorectal symptoms. There was no statistical difference in bacterial burdens between symptomatic and asymptomatic (CT difference of the means 0.52 copies/mL, 95% CI: [-0.51, 1.55]; P value = 0.313) (NG difference of the means 0.63, CI: [0.01, 1.28]; P value = 0.05).

Conclusions

In contrast to prior research, we found similar bacterial burdens in anorectal MSM samples with single CT/NG vs coinfection. Further research is needed to understand the clinical implications of CT/NG co-infections. Future should investigate factors influencing anorectal CT/NG bacterial burden, transmissibility, and susceptibility, including the function of PrEP and the rectal microbiota.

Key Messages

• Epidemiological and modelling studies have generated the hypothesis that the bacterial load in co-infections of Chlamydia trachomatis (CT) or Neisseria gonorrhoeae (NG) may be higher than that of either organism alone.

• In this study, we found no statistical evidence of differences in the bacterial load of CT or NG between single and co-infections in men who have sex with men (MSM) using HIV pre-exposure prophylaxis, and no differences in bacterial loads between symptomatic and asymptomatic individuals.

• Further research is needed to understand factors affecting bacterial load, transmissibility and susceptibility to anorectal CT and NG infections, including the roles of organism viability and prophylactic drug use among MSM populations.