Evaluating the impact of health reforms in the Netherlands: Assessing the impact of an alcohol ban on sexually transmitted infections in national surveillance data

Background: On 1 January 2014, the minimum age to buy alcohol increased (16–18 years), accompanied by a public awareness campaign (NIX18). Decreases in alcohol consumption are associated with less risky sexual behaviour. This study analyzed the association between the health reforms andChlamydia trachomatis infections (chlamydia) among young heterosexual people. Methods: Chlamydia positivity rates, age, and gender from all STI-clinic attendees between 16 and 19 years old in the Netherlands of 2010 to 2016 were obtained. Interrupted time-series assessed immediate and gradual trends in chlamydia rates. Results: Among the control group (18–19 year olds) chlamydia rates increased 0.5% each post-ban month (95% Confidence Interval [CI] 1.002–1.008, p = .001). Among 16–17 year olds there was no monthly increase post-ban (Rate Ratio 1.000, 95% CI 0.993–1.007, p = .948). In terms of confounders, only controlling for partner notification dissolved these time trends. Conclusions: We found that chlamydia rates after the alcohol ban differed between 16–17 year olds and 18–19 year olds. This demonstrates that the health reforms might have affected this secondary outcome, but obtaining certainty using national surveillance data is difficult. Specific studies should be designed, as now changes in chlamydia over time could be explained by STI-clinic policy changes, by changes on an individual level including reduced alcohol consumption or most likely by the combination of these factors.