A study presented at the recent 20th European AIDS Conference (EACS 2025) has found that the apparent rise in sexually transmitted infections (STIs), at least in gay and bisexual men with HIV in France, are due to more frequent testing rather than more infections.
Dr Sophie Novelli of the Centre for Epidemiology and Population Health (CESP) of the French national scientific health research agency INSERM presented data from 2016 to 2023 taken from the PRIMO cohort.
PRIMO is a long-standing cohort, founded in 1996, of people diagnosed with HIV during very early infection. It includes men and women of all sexualities and ethnicities, but about three-quarters of them are gay and bisexual men, and this study only included them. It collects data on HIV status, STIs, co-infections and sexual behaviour annually. Cohort members may be tested for STIs less or more often than annually, as STI tests are performed at the discretion of the physician, as suggested by STI symptoms and by the annual behavioural questionnaire. In practice, as the data below shows, screening tests for STIs, especially for chlamydia or gonorrhoea, were the exception rather than the rule in 2016.
As well as tracking STI incidence in the cohort, the study looked at changes in two other outcomes over time since 2016. One was the frequency of STI screening, expressed as the number of tests per PRIMO visit. The other was the positivity rate or ‘yield’, expressed as the number of positive diagnoses divided by the number of tests. A total of 1521 gay and bisexual men with PRIMO follow-up data from 2016-2023 were included.
Between 2016 and 2023 the proportion of men receiving a screening test for chlamydia increased from 8% to 56%, and for gonorrhoea from 6% to 55%. The blood test for syphilis was more standard in 2016, but still increased from 36% to 66%.
The incidence rate of all three STIs, expressed as the number of diagnoses per 100 men per year, increased from 5% to 11% for chlamydia, from 5% to 9% for gonorrhoea, and from 13% to 19% for syphilis. The influence of higher rates of testing can already be seen here; the increases in incidence of gonorrhoea and syphilis were not statistically significant, and the somewhat higher rate of diagnosis for syphilis is likely related to the greater number of syphilis tests during the seven years of follow-up.
The most interesting figure was the positivity rate, however: the percentage of positive diagnoses per screening test. This declined substantially for two infections, from 11% to 6% in the case of chlamydia and from 13% to 5% for gonorrhoea., and both these declines were statistically significant. The positivity rate per test for syphilis, however, stayed static at 16%.
“We observed an overall increase in both the screening and the incidence of STIs in recent years,” Novelli said. “However, the stable or declining positivity rates suggest that much of the observed increase in incidence may be driven by intensified screening rather than a true rise in transmission.”
It’s important to note that diagnoses made at the PRIMO screening tests may not reflect the total incidence rate in participants; they may have been tested and treated for symptomatic STIs between visits or at other healthcare facilities.
Overall, STI screening in study participants increased from 21% of men testing per year before 2018 to 49% afterwards as a result of national recommendations for testing at least once a year. Some sub-groups are now testing more than once a year, including 54% of younger men under the age of 25 and 71% of those with more than 10 partners a year testing for gonorrhoea. But there was no change over time in the behavioural profile of those testing that would have prompted more screening, so public knowledge about STIs, PrEP in HIV-negative people, and possibly doxyPEP may be contributing both to more tests and to fewer diagnoses per test.
Novelli S et al. Bacterial STIs incidence among MSM with HIV in France: the ANRS PRIMO cohort. 20th European AIDS Conference, Paris, abstract PS11.1, 2025.