Bacterial STI rates by pharyngeal, urethral and rectal sites among adolescents' men who have sex with men in Northeast Brazil: the importance of comprehensive sample collection sites


BACKGROUND: Comprehensive and timely detection of bacterial sexually transmitted infections (b-STI) is crucial to prevent transmission and sequelae of untreated infection. However, for adolescents' men who have sex with men (aMSM) the diagnosis of b-STI is still a challenge because they have little access to b-STI prevention, detection, and treatment services. Additionally, most infections are asymptomatic, especially when it occurs at rectal or pharyngeal sites. We aimed to estimate the rate of detection loss when using results from one collection site only (pharyngeal, urethral, or rectal) compared with results combining the three sites.
METHODS: Baseline data from the first PrEP demonstration cohort study among aMSM aged 15-19 years old going on in Brazil (PrEP1519). Eligible participants were enrolled between March 2019-August 2020 at Salvador site, Northeast Brazil. Swabs samples were collected from pharyngeal, urethral, and rectal sites and tested with qPCR for Neisseria gonorrhoeae (NG), Chlamydia trachomatis (CT) and Mycoplasma genitalium (MG). Proportions were estimated by collection site and in combination.
RESULTS: For NG the rate of detection loss was 34.2% (11 participants), 50.8% (18), and 89.5% (29) when only the pharyngeal site, the rectal site, the urethral site was analyzed respectively. For CT the loss rates were 67.6% for the pharyngeal site, 61.8% for the rectal site and 64,7% for the urethral site. For MG the loss rates were 36.4%, 63.64%, 81.84% when only rectal, pharyngeal, and urethral samples were analyzed, respectively. There were significant differences in the detection of NG using rectal and urethral samples and in the detection of MG using urethral samples.

Table 1. b- STI prevalence and detection loss rates by collection site and combined sites

STIThree sites combined
(n =177)
n (%)
Only pharyngeal
(n =177)
n (%)
Detection loss (%)p-valueOnly rectal
(n =158)
n (%)
Detection loss (%)p-valueOnly urethral
(n =160)
n (%)
Detection loss (%)p-value
NG32 (18.1)21 (11.9)34.20.1314 (8.9)50.80.023 (1.9)89.50.001
CT6 (3.4)2 (1.1)67.60.172 (1.3)61.80.292 (1.2)64,70.28
MG11 (6.2)7 (3.9)37.10.474 (2.5)59,70.122 (1.2)80.60.02

CONCLUSIONS: Our data shows that comprehensive and timely detection of b-STI is quite important and can lead to early treatment of existing and prevention of new infections especially in young MSM. This measure, associated with an effective prevention policy, can contribute to better control of the spread of b-STI.