Screening for Chlamydia trachomatis

Abstract

Opportunistic approaches have little evidence to support them

Sexual infections and teenage pregnancies disproportionately affect people living in poverty and social exclusion. In 2004, the government white paper “Choosing health”¹ identified sexual health as a priority area for improvement and service development. The paper followed the publication of the National Strategy for Sexual Health and HIV,² which aims to provide “better prevention, better services, and better sexual health.” The strategy described the implementation of a broad National Chlamydia Screening Programme (NCSP) in accordance with the National Health Service plan, which included “a commitment to improving the prevention of ill health and providing screening programmes where they are appropriate.” In this week's BMJ, an analysis by Low shows how acceptance of the effectiveness of chlamydial screening programmes in Sweden and the United States supported the funding of the National Chlamydia Screening Programme before the balance of benefits and harms was thoroughly understood.³

Chlamydia is the most common sexually transmitted disease in England. Its prevalence has increased steadily since the mid-1990s, and rose by 300% from 1995 to 2004. The main burden of infection affects women aged 16-19 and men aged 20-24 years. Although often asymptomatic, associated problems such as pelvic inflammatory disease, infertility, ectopic pregnancy, epididymo-orchitis, ophthalmic complications, and neonatal complications are well described. As with most sexually transmitted infections, Chlamydia trachomatis may be a cofactor for HIV transmission.

Chlamydia is the only sexually transmitted infection for which population screening has been implemented. Ideally, a screening programme for infectious disease should identify and treat a sufficient number of infections to reduce transmission in the community, and thus reduce prevalence. There are two main approaches to the design of screening programmes—proactive and opportunistic. Proactive screening—for example, cervical screening in the United Kingdom—uses the population register to identify the target population. People are contacted at intervals defined by the transmission dynamics (which use epidemiological data to estimate the spread or transmission of infection in the absence of intervention within a defined time frame), uptake of screening is monitored, and non-attenders are contacted. Opportunistic screening targets people who attend a healthcare setting. Thus, it reaches only those who attend the service and regular rescreening is unlikely to occur. It also relies upon the health provider remembering to give information and offer the test to those deemed eligible.

The National Chlamydia Screening Programme in England began in 2001.⁴ It uses an opportunistic approach and targets sexually active people under 25 years of age within a variety of healthcare settings. It is a dynamic model, which evolves as evidence accumulates. In the third year of the programme, 1777 venues were involved in 26 programme areas, and nearly 100 000 people were screened. Most of these people were women (82%). The incidence of chlamydia infection was 10.1% (95% confidence interval 10.0 to 10.3). Of 8816 positive cases, around 10 000 partners were reported; 49% of partners were tested and 33% were treated. This may seem like a low proportion, but contact tracing is notoriously difficult. In a prior attempt to develop national standards for measuring outcomes of care for gonorrhoea and chlamydia in genitourinary medicine clinics, reports detailing chlamydia outcomes were identified. In large city clinics, 0.43 (0.30 to 0.62) contacts per case were screened compared with 0.64 (0.58 to 0.70) contacts per case in other clinics.

The analysis by Low³ cites a lack of evidence from randomised controlled trials to support the opportunistic screening method. The opportunistic approach is used in most chlamydia screening programmes in the US, Sweden, and England. Studies showing a reduction in the rates of chlamydia, pelvic inflammatory disease, and ectopic pregnancy over time have been widely cited in support of such screening.^{5 6} A concurrent decrease in the diagnosis of gonorrhoea in Sweden and the UK has occurred, but has been ascribed to extensive safe sex campaigns rather than the chlamydia screening programme. However, rates of chlamydia in Sweden, the rest of Europe, and the US have been steadily increasing since the mid-1990s despite the implementation of opportunistic screening. This increase in rates may reflect the outcomes of targeting more people, the use of more sensitive technology, or a genuine increase in prevalence.

Critics of the National Chlamydia Screening Programme have focused on several issues. These include the use of an opportunistic screening method and its associated fragility; the reduced participation of general practitioners in the programme compared with the pilot schemes, in which doctors were paid for each patient enrolled and participation was mandatory; the low number of men screened; contact tracing failing to reach all partners; and cost effectiveness. In two pilot sites, all general practitioners took part, were paid for each patient enrolled,⁵ and generated the highest proportion of tests and cases, achieving an effective screening rate of 50%.³ In the programme itself, participation of general practitioners is optional and largely unremunerated. In 2005-6, the effective screening rate was less than 5% in more than half of programme areas. However, the National Chlamydia Screening Programme is in its third phase of conception and is still expanding, with a large scale implementation due later this year. It has responded with innovative strategies, such as pharmacy based screening programmes, to reach target groups.

A proactive approach to chlamydia screening might be difficult and unacceptable to some people, as screening would start at 16 years of age and not all of those invited would be sexually active. As the aim of the programme is to reduce the prevalence of chlamydia, infected men would need to be identified, and this might have a significant impact on its cost effectiveness. Strategies from the men's health forum study (supported by the Department of Health), such as depositing test kits and health promotion literature in the workplace, may prove useful.⁷ Cost is being questioned by Low³ in light of conflicting opinions regarding the prevalence of morbidity related to chlamydia, and mathematical modelling relies on high levels of acceptance, uptake, and coverage of screening, in addition to annual repeat testing and partner notification—areas that are continually being developed in the National Chlamydia Screening Programme.

The Department of Health has recruited the National Institute for Health and Clinical Excellence (NICE) to produce public health guidance on interventions, including screening, designed to reduce the transmission of chlamydial infection, together with other sexually transmitted infections and pregnancy in the under 18s.⁸ Recommendations include identifying people at risk of infection and providing sexual health counselling. One to one interventions, as well as group and peer based approaches, are highlighted throughout the document. It discusses partner notification and treatment; evidence based methods that have yielded higher contact rates than conventional contact tracing, such as mailing home sampling urine kits and patient delivered partner therapy (this strategy is not legal in the UK). Primary care trust commissioners are asked to ensure that sexual health services are in place to meet local needs.

Sexual health has emerged as a government priority. Despite multiple campaigns in the media, the diagnosis of sexually transmitted infections continues to increase. Most people who are affected are unlikely to seek sexual health testing and may only be assessed via a proactive approach rather than the opportunistic screening programme currently offered.