Impact case study database

Natsal is the primary source of information about sexual behaviour and sexual health service use in Britain, and has influenced the design and delivery of other national sex surveys, including those in Ireland, Germany, Slovenia, Australia, New Zealand, and the US. Natsal’s international impact has been recognised by its choice as an example in the World Health Organization’s development of a standardised, population-representative sexual health survey instrument [S1].

In Britain, Natsal is used widely by policymakers, clinicians and service planners to design, deliver and monitor a number of sexual and reproductive health strategies. For example, Natsal was recognised in the House of Commons’ Health and Social Care Committee’s Inquiry into Sexual Health in 2019, which sought to identify priority areas for the next national strategy to help both providers and commissioners deliver sexual health services to a high quality and consistent level [S2]. Natsal’s submission cited evidence from 37 peer-reviewed articles (including [R1] to **[R7]**) to inform this prioritisation exercise. Impacts since 2013 include:

Evidence to inform HPV vaccination policy: As the world-leading research resource on sexual health, due to its unique size, detail and quality, Natsal provides the underlying population behavioural and biological parameters (e.g. sexual mixing patterns by age and gender at a population level) that are essential for transmission models of the impact and cost-effectiveness of HPV vaccination programmes in the UK and internationally. These are repeatedly used by the Department of Health’s Joint Committee on Vaccination and Immunisation’s (JCVI) to model effectiveness and cost-effectiveness and recommend (i) extending vaccination to men who have sex with men (MSM) in JCVI’s 2015 statement on HPV vaccination in MSM [S3], and (ii) in its July 2018 statement recommending extending the HPV vaccination programme to adolescent boys [S3]. The reach of this impact extends to a number of countries that use these parameters to inform decision-making, for example 2016 research led by the International Agency for Research on Cancer used Natsal’s HPV transmission model to show links between age-specific sexual patterns and HPV vaccination effectiveness, considering rural India and the USA as examples of two heterosexual populations with tradition and gender-similar age-specific sexual behaviour [S4].

Contributing to the National Chlamydia Screening Programme (NCSP): Public Health England (PHE) delivers the NCSP and relies on Natsal to understand the risk of chlamydia infection within the general population; co-infection with other STIs; knowledge of risk; and the factors associated with risk; as described in its 2017 evidence pack for external peer reviewers [S5]. This intelligence has contributed, for example to the 2020 ‘State of the nation’ report by the Terrence Higgins Trust, which cites Natsal evidence alongside its recommendations to reduce societal inequalities in levels of chlamydia infection: “ research using the Natsal-3 survey highlighted the potential impact of poverty. It found higher prevalence of chlamydia among women living in deprived areas despite testing rates not being any higher” [S6].

Shaping screening and clinical guidelines for (other) STIs and sexual health service delivery: Importantly, Natsal captures those who do - as well as those who do not - attend services, which is especially important as STIs can be asymptomatic and stigmatised. For cases diagnosed in sexual health clinics, Natsal provides the population-based perspective and informs appropriate screening strategies. For example, the low prevalence of gonorrhoea in the general population raises the issue of false positives, as outlined in PHE’s national guidance on the management of gonorrhoea (2014): “A recent population-based survey [Natsal] detected gonorrhoea only in those aged 20-24 years; in this age group the prevalence was 0.1% in men and 0.2% in women…..despite excellent specificity, high rates of false positive tests can occur due to low gonorrhoea prevalence in the population tested and the potential for cross reaction with non-gonococcal neisseria species” [S7]. Also, Natsal’s evidence that there are differences in the age- and sex-specific prevalences of chlamydia and M. Genitalium (MGen), with higher prevalence in older age groups than those targeted in the NCSP, has formed the basis for the BASHH’s 2018 national guidelines for the management of infection with MGen, which recommends the management of patients who are symptomatic and attend services, rather than a population-based MGen screening programme in young people [S7].

Impact on HIV prevention, control and service provision: Natsal data are essential for use in mathematical models used by PHE for estimating the national burden of HIV. The models combine anonymous prevalence surveillance data with Natsal’s estimates of the size of the population at risk to estimate the number infected and the proportion who remain undiagnosed [S8]. In addition, Natsal parameters and data have been used to evaluate the cost-effectiveness of key interventions, including the roll-out of pre-exposure prophylaxis (PrEP) for HIV, as described in an NIHR-funded analysis published in Lancet Infectious Diseases which showed that introduction of PrEP could result in a GBP1bn cost saving and prevent 25% of HIV infections within 15 years [S8]. Natsal also continues to inform national HIV prevention efforts by providing robust underpinning evidence, for example those run by charity the National AIDS Trust in its 2015 report ‘Preventing HIV in the UK heterosexual population’: “HIV transmission studies and prevention interventions for heterosexuals are mainly built on an assumption of vaginal sex as the primary route of transmission. The most recent Natsal survey has found an increase in the number of respondents reporting anal sex. In 2010-12, 15% of women reported anal sex, compared with 11% in 1999-2001…HIV prevention efforts should consider specific behavioural risks and prevention needs of heterosexuals, for example anal sex and partner numbers, just as we do for MSM.” [R7], [S8].

Evidence to address health inequalities: Natsal-3 demonstrated how MSM are disproportionately affected by a range of harmful health behaviours and poor health outcomes, and this contributed to the evidence base informing national guidelines to identify problematic recreational drug and alcohol use among MSM as a marker for increased STI risk [S9]. Similarly, Natsal-3’s evidence of a greater burden of poor sexual health among ethnic minorities is recognised by BASHH and the Terrence Higgins Trust in their 2020 ‘State of the Nation’ report, leading them to call commissioners to translate the evidence into effective targeted prevention interventions as part of their provision of sexual health services [S6].

Impact on Sex and Relationship Education (SRE): Natsal informs the content and delivery of evidence-based SRE, including in public-facing resources disseminated by sexual health charities e.g. Brook , Relate, PSHE Association, and the Sex Education Forum (SEF). According to SEF’s Director, Lucy Emmerson: “[we] quote [Natsal] [in everything we do and we have made it accessible for approximately 100 partner organisations and network of hundreds of schools” [S10]. In November 2014, Natsal collaborated with the SEF to deliver ‘SRE: Coming of Age’, a conference to pre-release Natsal-3’s SRE-related findings to those involved with the (then) Education Select Committee Inquiry into SRE, and those working in local authorities who received SEF’s ‘A briefing for local councillors on Relationships and Sex Education’. This included bespoke infographics created from Natsal-3 data to share with and inform their Directors of Public Health. According to the SEF, Natsal research played a key part in the Education Select Committee concluding that SRE should be statutory [S10].

Contribution to public engagement activities on sexual health: Natsal has played a key role in contributing to public conversations about sex (for example Mercer’s 2014 TEDx talk about the realities of people’s sex lives; >250,000 views; 1,700 likes **[S11]**) and promoting the public’s understanding of sex research. Natsal was the inspiration for the Wellcome Collection’s highly successful ‘Institute of Sexology’ exhibition in 2015, which was accompanied by 117 live events and 82 workshops, attended by 8,600 participants. This was accompanied by a book named after the exhibition, and also Professor Sir David Spiegelhalter’s book ‘Sex by numbers’, that showcased Natsal as one of the few examples of high-quality research into sexual behaviour.