Sexual health is an important component of physical and mental health. In the UK, rates of teenage pregnancy are among the highest in western Europe and sexually transmitted infections (STIs) such as chlamydia are common in teenagers and young adults. Sexual behaviour is a normal part of human development and it is crucial to understand the factors that influence sexual health and behaviour through this development process in adolescence to guide suitable public health interventions to improve sexual health.

The ALSPAC cohort is representative and extremely well characterised from before birth. The ALSPAC children are now teenagers, and this offers a unique opportunity to study adolescent sexual behaviour and adverse sexual health outcomes, including sexually transmitted infections. Sexual activity has been measured at age 11, 12, 13+, 15+ and factors affecting relationships between the individual and his/her environment have been measured across the life-course. We propose to repeat the sexual activity questionnaire at the age 17+ clinics and in addition, collect biological samples to test for current and past chlamydia and human papillomavirus (HPV) infection. These infections are common and important in terms of public health policy given the recent introduction of the National Chlamydia Screening Programme and imminent HPV vaccine introduction. Using this data, we will describe the sexual behaviour and prevalence and incidence of chlamdyia and HPV in teenagers, and identify risk factors for adverse sexual health outcomes. By doing so, we aim to identify potentially modifiable behaviours/ factors that can be used to develop sexual health interventions for young people.

Aims:

- To describe the sexual behaviour of ALSPAC participants attending the age 17+ clinics

- To establish the prevalence of current and past infection with chlamydia in ALSPAC participants attending the age 17+ clinics

- To establish the prevalence of current and past infection with HPV in ALSPAC participants attending the age 17+ clinics

- To measure associations between sexually transmitted infections with current and past sexual behaviour and other risk taking behaviours

- To establish early-life influences and predictors of adverse sexual health outcomes

Methods:

We propose to engage the cohort in the next round of clinics at age 17+ years. Participants attending the clinics will be invited to complete a computer assisted self-interview (CASI) on 'romantic relations' and other relevant risk behaviours, particularly substance use. The romantic relations questionnaire was first introduced at the age 11+ clinic and to maintain consistency between assessments we will retain this questionnaire. However, we will also assess whether further questions should be added, for example, to allow direct comparisons with NATSAL. Participants will be invited to give blood and first catch urine samples which will be used to test for active and past infection with chlamydia and HPV (see below). In addition, informed consent will also be sought to test stored samples collected in the age 15+ and 13+ clinics.

These data will be analysed to describe the age-specific sexual behaviour and the incidence and prevalence of HPV and chlamydia. We will then identify risk factors for HPV and/or chlamydia infection over life course and associations with other risk taking behaviours. Predictor variables from biological, individual, family, peer, social and cultural domains will be considered for inclusion in regression models.