Temporal trends and public health interventions shaping STI notifications in Portugal, 2014–2023

Background

Sexually transmitted infections (STIs) have re-emerged globally. In Portugal, as in other European countries, notifications of syphilis, gonorrhoea, and chlamydia increased markedly after 2015. This change occurred during a period of changes in surveillance systems and the expansion of testing and delivery of HIV pre-exposure prophylaxis (PrEP). This study aimed to describe national trends in STI notifications from 2014 to 2023 and to assess the effect of these public health interventions on these trends.

Methods

We conducted an ecological study using Portuguese yearly surveillance data on syphilis, gonorrhoea, and chlamydia, retrieved from the ECDC Atlas (2014–2023). Interrupted time-series analysis, estimated via Poison regression model was used to calculate immediate (level change) and sustained (slope changes) effects following key interventions: laboratory-based notification (2016), expansion of community-based testing (2017), PrEP introduction (2018), and revision of case definitions (2021). Separate models were fit for each intervention.

Results

STI notifications had an average annual increase of 31%, with syphilis showing the steepest trend. Syphilis notifications showed the largest immediate increase (IRR=3.80; 95% CI: 3.15–4.63) and sustained growth (IRR=1.23; 95% CI: 1.11-1.36) following the introduction of PrEP. The expansion of community-based testing was followed by immediate increases in three STIs’ IRR. In contrast, the revision of case definitions in 2021 was followed by reductions in notifications, particularly for chlamydia. Gonorrhoea showed short-term increases across all interventions, without consistent sustained changes.

Conclusions

Changes in STI notifications followed major public health interventions related to surveillance, testing, and prevention. These findings suggest that part of the observed increase in STIs notifications may reflect improved case detection and notification rather than transmission alone.

Key messages

• Public health interventions were followed by increases in STI notifications, particularly for syphilis, reflecting the effects of expanded case detection and reporting

• Increases in STI notifications may reflect improvements in surveillance and testing rather than transmission alone, highlighting the importance of evaluating public health interventions