Sexual transmission of infections across Europe: appraising the present, scoping the future

Key points on the epidemiology of bacterial STIs reported to ECDC from EU/EEA

• Reported numbers of bacterial STIs (chlamydia, gonorrhoea, syphilis, LGV) reached an all-time high in 2019.

• Heterogeneity in surveillance systems (comprehensive vs sentinel surveillance, compulsory vs voluntary notification, case based vs aggregated data) and variable levels of reporting completeness must be considered when comparing data across countries. Concerted efforts are needed to harmonise a Europe-wide data collection.

• Improved diagnostic capacity (especially for chlamydia and LGV) and expanded testing programmes (eg, for HIV-negative MSM) partially explain increases in STI reporting rates.

• Reflecting high screening rates, chlamydia remains the most frequently reported STI; although it is most common in young women, reported cases doubled among MSM between 2015 (13 per 100 000) and 2019 (25 per 100 000).

• Reported LGV cases occur predominantly among MSM living with HIV but are increasing among HIV-negative MSM (likely also because of improved case ascertainment).

• Reported cases of gonorrhoea are three times more common among men than in women. Young women are a vulnerable group, with a median age at diagnosis of 22 years vs 26 years for heterosexual men and 31 years for MSM.

• Syphilis continues to be a largely male-dominated epidemic. MSM account for 68% of cases with information on transmission available, and diagnoses are increasing among HIV-negative MSM. People diagnosed with syphilis tend to be older than those diagnosed with gonorrhoea or chlamydia (median age 36 years for MSM, 35 years for heterosexual men, 29 years for women).

• Notifications of congenital syphilis remain low, although the overall notification rate increased from 1.1 to 1.9 cases per 100 000 live births between 2015 and 2019, with some countries reporting disproportionately high numbers.

• Underdiagnosis and under-reporting of STIs are anticipated for 2020/2021 due to the COVID-19 pandemic. Factors that are expected to modify STI epidemiological trends include changes in sexual behaviour and healthcare-seeking behaviour, alongside variations in healthcare availability and mode of delivery. More research is needed to understand these effects.

ECDC, European Centre for Disease Prevention and Control; EEA, European Economic Area; EU, European Union; LGV, lymphogranuloma venereum; MSM, men who have sex with men.

Chlamydia

In 2019, 434 184 chlamydia cases were reported by 26 countries. The total notification rate (per 100 000 population) was 157, with rates ranging from <1 (Cyprus, Greece, Romania) to >500 (Denmark, Iceland, Norway). As in previous years, the UK reported ~60% of total cases (a notification rate of 389 per 100 000), which reflects the existence of a national chlamydia screening programme. The male to female ratio in total EU/EEA cases was 0.8:1; 60% of reported cases were in individuals aged 15–24 years, a group which has high incidence of chlamydia and is targeted by testing policies.6 For cases with reported modes of transmission, 82% were in heterosexual women and men and 13% in men who have sex with men (MSM).

Gonorrhoea

In 2019, a record number of 117 881 gonorrhoea cases were reported from 27 countries. The total notification rate (per 100 000 population) was 32, with rates ranging from <1 (Bulgaria, Cyprus, Poland, Romania) to >30 (UK, Denmark, Iceland, Ireland, Malta, Norway, Sweden). The UK reported 66% of total cases and had the highest notification rate of 116 per 100 000. The male to female ratio in the total EU/EEA cases was 3.1:1. For cases with reported modes of transmission, 48% were in MSM, 24% in heterosexual women and 22% in heterosexual men; the prevalence rates of reported HIV infection in these cases were 19%, 0.6% and 1.3%.

Syphilis

In 2019, there were 35 039 syphilis diagnoses reported by 27 countries. The total notification rate (per 100 000 population) was 7.4, with rates ranging from <3 (Croatia, Estonia, Slovenia, Romania) to >10 (UK, Iceland, Ireland, Malta, Spain). The male to female ratio in the total EU/EEA cases was 8.6:1. Considering cases where HIV status was reported, 4% of heterosexual cases and 31% of MSM cases occurred in people living with HIV. While the number of cases of syphilis remained stable in MSM living with HIV during 2015–2019, there was a 44% increase in syphilis diagnoses among HIV-negative MSM. There were 72 notifications of congenital syphilis in 2019. The notification rate for the EU/EEA (1.9 cases per 100 000 live births) fell below WHO elimination target (<50 cases per 100 000 live births). The number of countries reporting cases (among those reporting data) decreased from 17 of 24 (71%) in 2010 to 13 of 25 (52%) in 2019; 6 of 23 countries that reported consistently through the years (Cyprus, Iceland, Luxembourg, Malta, Norway, Slovenia) recorded no cases during 2010–2019. However, the total notification rate increased from 1.1 in 2015 to 1.9 in 2019, and Bulgaria and Portugal reported disproportionately high numbers in 2019 (37 of 72 and 12 of 72 notifications, respectively).

Lymphogranuloma venereum

A total of 3112 LGV diagnoses were reported from 16 countries in 2019, whereas there were 103 cases reported by two countries (UK, Netherlands) in 2004. The increase likely documents an expanding LGV epidemic, but also indicates improving diagnostic capacity. Between 2004 and 2019, 99% of cases with reported modes of transmission occurred in MSM, and 73% of MSM cases with reported HIV status were in MSM living with HIV. Since 2015, in parallel with a sustained increase in the number of LGV cases among MSM living with HIV, data indicate an increase in LGV diagnoses among HIV-negative MSM.7 8 The true magnitude of the epidemic is likely to be underestimated because of the scarcity of routine screening data.