Spontaneous clearance of urogenital, anorectal and oropharyngeal and in women, MSM and heterosexual men visiting the STI clinic: a prospective cohort study.

Objective: (CT) and (NG) infections can clear without treatment. Despite high prevalence of anorectal infections in men who have sex with men (MSM) and women, studies on anorectal clearance are scarce. Moreover it is unknown whether bacterial load affects urogenital/anorectal CT clearance. In this prospective cohort study, CT and NG clearance is assessed at three anatomical sites of men and women.

Methods: CT-positive and NG-positive MSM, heterosexual men and women ≥18 years of age visiting our STI clinic between 2011 and 2013 underwent a repeat test when returning for treatment (n=482). The primary outcome was clearance, defined as a positive nucleic acid amplification test (NAAT) at screening-consultation, followed by a negative NAAT at treatment-consultation. Sociodemographics, sexual risk behaviour and CT bacterial load (inhouse quantitative PCR) were tested as determinants for clearance using multivariable logistic regression for CT and Fisher's exact test for NG.

Results: CT clearance was 9.1% (10/110) for urine, 6.8% (20/292) for vaginal swabs, 12.7% (8/63) for anorectal swabs (ie, 4.0% [1/25] in MSM and 18.4% [7/38] in women) and 57.1% (4/7) for oropharyngeal swabs. For NG this was 33.3% (2/6), 28.6% (2/7), 20.0% (2/10) and 27.3% (6/22), respectively. The number of days between tests (median 10, IQR 7-14) was not associated with clearance. Lower bacterial load at screening was the only predictor for CT clearance (urine mean 1.2 vs 2.6 log CT/mL, p=0.001; vaginal swabs mean 2.1 vs 5.2 log CT/mL p<0.0001; anorectal swabs mean 2.0 vs 3.7 log CT/mL, p=0.002). None of the tested determinants were associated with NG clearance.

Conclusions: This study reports the largest number of anorectal infections tested for CT and NG clearance to date. Clearance in all sample types was substantial: between 7% and 57% for CT, and between 20% and 33% for NG (notwithstanding low absolute numbers). CT clearance was associated with a lower load at screening. However, not all individuals with low bacterial CT load cleared the infection, hampering STI guideline change.