Chlamydia is the most common treatable sexually transmitted infection in the UK, and is particularly common in sexually active men and women aged under 25. While it is easily treated using antibiotics, it often has no symptoms so many people are not aware they have an infection. Untreated chlamydia can lead to health complications, including pelvic inflammatory disease, chronic pelvic pain, ectopic pregnancy, epididymitis (discomfort, pain and/or swelling in the testicles in men) and infertility.
Policy makers have recognised the public health importance of chlamydia control, introducing specialist youth-focused services in many countries, and national screening programmes in England, USA and Sweden. Despite this, there remain gaps in the evidence that is needed for ensuring that chlamydia control policies meet the needs of those most at risk. One of these areas of uncertainty is about whether or not there are socioeconomic inequalities in infections. This has important implications for policies to reduce inequalities in sexual health. If disadvantage is associated with risk of infection, this could indicate a need for increased delivery of chlamydia testing and treatment services in disadvantaged areas.
As part of my DECIPHer PhD research, I worked with colleagues at the University of Bristol to examine the prevalence of chlamydia (proportion of people in the population who have the infection) and whether chlamydia infection was associated with socioeconomic disadvantage. This research has recently been published in a paper in PLOS ONE.
We used data from the Avon Longitudinal Study of Parents and Children (ALSPAC, or ‘Children of the 90s’), a cohort of young people born in 1991 and 1992 in the Bristol area. We asked the 9568 eligible young people to provide a urine sample at a research clinic when they were about 17 years old. These samples were tested for chlamydia by a local laboratory. The local chlamydia screening service provided usual care for participants, informing them of the results and making arrangements for accessing treatment where necessary. All eligible young people in the ALSPAC cohort were encouraged to take part in the chlamydia test, not just those who reported being sexually active.
To look at relationships between social disadvantage and chlamydia infection, we used information provided by ALSPAC mothers on household income, occupation, and mother’s educational qualifications. We also collected information on neighbourhood deprivation from the young people’s postcodes at age 17, and data on the young people’s educational attainment at age 10-11 and GCSE. Measuring socioeconomic position based on exam results may at first glance seem a strange approach. However, more conventional measures such as income and type of occupation are not so relevant for young people. Numerous studies of chlamydia infections use academic attainment to measure inequalities because it is associated with parental socioeconomic position and is often easier to measure.
After adjusting for differences between participants who consented to test for chlamydia and those who did not, we estimated that chlamydia prevalence in men and women aged 17 was 2%. There is uncertainty about this prevalence estimate because only 20 out of the 2904 who were tested were found to have chlamydia. However, we can be reasonably confident that the true result lies between 1% and 3%. Our ALSPAC results are within the same range as those of Natsal-3, a recent nationally representative study.
However, the most striking result from the study was that there was a strong link between chlamydia infection and social disadvantage. For example, young people from families with lower disposable income or whose mothers had fewer educational qualifications were more likely to have chlamydia infections. Young people’s own educational attainment was also associated with chlamydia infections. Young people with lower results in national tests at age 10-11 and at GCSE were more likely to have chlamydia than peers with higher results. These results held even after adjusting for potential confounders – other factors that might distort the relationship between disadvantage and chlamydia infections.
There are several possible ways that socioeconomic disadvantage may increase risk of chlamydia infections. For example, experience of disadvantage may reduce the perceived benefits of safe sex, reduce consistency of condom use, and reduce use of sexual health service services. Disadvantage may also increase other risk factors for unsafe sex such as alcohol and substance use, and mental health problems. As discussed above, young people’s educational attainment may be associated with chlamydia infection because it tends to reflect their levels of socioeconomic advantage. Educational achievement may also be protective if it raises the perceived benefits of safe sex, increases access to information and encourages healthy behaviours.
These results are important because they suggest that inequalities in chlamydia infections among 17 year olds in England may continue to be a problem despite the introduction of a chlamydia screening programme in 2007. Screening is offered to young people when they access health services for other reasons, as well as being available in pharmacies and other community settings. Although the screening programme’s target group includes everyone who is sexually active aged 15 to 24, in practice not everyone will receive an invitation or will accept a test offer. Differences in uptake may mean that testing is distributed unevenly and therefore screening may not address health inequalities or could even make them worse. Two studies show that England’s National Chlamydia Screening Programme has made efforts to ensure equal uptake, providing more screening services in disadvantaged areas. However, another more recent study showed uptake of screening services is similar across all levels of neighbourhood deprivation, meaning more may need to be done in order to increase uptake of screening in disadvantaged areas. It’s also important to note that there were cases of chlamydia infection at all levels of socioeconomic advantage in our study, underscoring the value of a universal approach to provision of chlamydia testing services.
About the author: Jo Crichton is a DECIPHer PhD student based at the University of Bristol. Her PhD research is looking at peer-led intervention to promote chlamydia testing.
This piece summarises the following paper:
Crichton J, Hickman M, Campbell R, Heron J, Horner P, et al. (2014) Prevalence of Chlamydia in Young Adulthood and Association with Life Course Socioeconomic Position: Birth Cohort Study. PLoS ONE 9(8): e104943. doi:10.1371/journal.pone.0104943
The full paper is available, open access, here: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0104943