Background The bacterial load of Chlamydia trachomatis (CT) infected individuals may indicate the likelihood of further transmission and development of sequelae. This is the first and largest study to date providing results of a complete overview of the bacterial CT-load of genital and extra-genital samples and its associations with Neisseria gonorrhoeae (NG) infection and HIV.

Methods All genital (n=2,067 vaginal swabs; n=1,793 urines), anorectal (n=828) and oropharyngeal (n=61) nucleic acid amplification test (NAAT) CT-positive samples from the Maastricht Medical Microbiology Laboratory were included in analyses (2012–2016). The NAAT cycle quantification (Cq)-value was used as an inversely proportional measure for CT-load (Cq-values and CT/ml values were highly correlated for vaginal swabs; Pearson’s r:-0.9, and moderately correlated for urine in men; Pearson’s r:-0.6; p<0.001). Mean Cq-values were compared between anatomic locations and coinfections with HIV and NG. Mean Cq-values are presented and tested using ANOVA and independent T-tests stratified for sex. Only statistically significant associations (p<0.05) are presented.

Results In men, Cq-values were higher in oropharyngeal swabs and anorectal swabs compared to urine (35.9 and 33.9 vs 32.7; p<0.01). Men with urogenital NG had higher urine Cq values than men without urogenital NG (33.9 vs 32.6;p<0.01). Cq values were higher in urines of HIV positive men compared to HIV negative men (33.9 vs 32.7;p<0.01). In women, Cq-values were higher in oropharyngeal swabs and anorectal swabs compared to vaginal swabs (36.7 and 33.9 vs 30.8;p<0.001). Cq-values were higher in vaginal swabs of HIV positive women compared to HIV negative women (35.1 vs 31.0;p=<0.01).

Conclusion Vaginal swabs and urine samples had much lower Cq values, i.e. higher CT loads, compared to oropharyngeal swabs which could have impact on transmission potential and sequelae. We hypothesize that high risk populations, such as HIV and NG positive patients, likely have repeat CT infections leading to partial immunity and therefore lower CT loads.

Disclosure No significant relationships.