Sexually transmitted infection (STI) incidence in men who have sex with men (MSM) followed since primary infection stage in the French ANRS-PRIMO cohort

Background: In France, in a context of rising at-risk sexual behaviour in MSM, we estimated the incidence rate of STIs in HIV-infected MSM followed since primary HIV infection. We compared these incidence rates according to the viral load of patients at the visit preceding the STI diagnosis.
Methods: In 1996-2014, 1,226 MSM have been enrolled in the ANRS-PRIMO cohort during primary HIV-infection. Patients are followed every 6 months. At each visit, a clinical questionnaire is completed with lab measurements, antiretroviral treatment and clinical information including STI occurrence since the last visit.
We focused on syphilis, gonorrhea, Chlamydia trachomatis infections, and other suspected bacterial infections such as unspecified uretritis, rectitis, epididymitis, orchitis and balanitis. We assumed that two episodes of the same STI were distinct infections if separated by ≥3 months, and by ≥1 year for syphilis. We assessed the evolution over time in incidence rates and their association with the viral load of the patients measured at the visit preceding the STI diagnosis with a regression model of Poisson taking into account longitudinal data.
Results: We observed 412 incident STIs in MSM, i.e. an incidence rate of 6.67/100 patient-years (PY) [95%CI: 6.05-7.34], including 215 syphilis (incidence rate: 3.61/100PY [3.16-4.13]) and 197 other bacterial STIs (incidence rate: 3.19/100PY [2.77-3.66]).
The syphilis incidence rate was null before 2000 and increased afterwards of 9% per year on average (p< 0.0001) up to 4.91/100PY in 2013. As well, the other STIs incidence rate increased over time of 4% per year (p=0.006) up to 4.40/PY in 2013.
Considering all STIs together throughout 1996-2014, the incidence rate during the periods when MSM had an undetectable viral load was lower compared with the periods with detectable viral load (6.08/100PY versus 7.72/100PY, p=0.02).
Conclusions: In these HIV-infected MSM, STIs incidence has risen over calendar time, in syphilis as well as in other bacterial infections. Although they may be underestimated because of under-reporting or under-diagnosis, these incidence rates were high, particularly when the viral load is detectable. With the diffusion of the concept of Treatment as HIV Prevention, efforts should be done to help MSM to prevent transmission of other STIs.

K. Champenois1, R. Seng1,2,3, A. Persoz1, A. Essat1, C. Goujard1,2,4, L. Meyer1,2,3, ANRS PRIMO Cohort Study Group
1Inserm UMR 1018, CESP-4, Epidemiology of HIV and STIs, Le Kremlin Bicêtre, France, 2South-Paris University, South-Paris Medical School, Le Kremlin Bicêtre, France, 3AP-HP, Bicêtre Hospital, Epidemiology and Public Health Service, Le Kremlin Bicêtre, France, 4AP-HP, Bicêtre Hospital, Internal Medicine Department, Le Kremlin Bicêtre, France