The English National Chlamydia Screening Programme: Variations in Positivity in 2007/2008 : Sexually Transmitted Diseases

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The English National Chlamydia Screening Programme: Variations in Positivity in 2007/2008

Simms, Ian PHD*; Talebi, Alireza MSC*; Rhia, Johanna MSC*; Horner, Paddy MD; French, Rebecca S. PHD; Sarah, Randall MD*; Macintosh, Mary MD*

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Sexually Transmitted Diseases: August 2009 - Volume 36 - Issue 8 - p 522-527
doi: 10.1097/OLQ.0b013e3181a2aab9
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The national chlamydia screening programme (NCSP) seeks to offer screening to all sexually active people under the age of 25, a population of 5.3 million people.1 Screening, which is recommended every 12 months or with partner change, is delivered in the community outwith Genitourinary Medicine clinics through a diverse range of healthcare and nonhealthcare settings.1 Each of the 152 English primary care organisations (PCO) is responsible for commissioning and implementing services they consider appropriate to the healthcare needs of their local population. The execution of the NCSP has occurred in 3 phases between 2003 and 2007 to minimize the burden placed on service providers. Phases 1 (2003/2004), 2 (2004/2006), and 3 (2006/2008) included 14, 35, and 103 PCOs, respectively. Full participation by all PCOs was achieved by April 2007 and it was for this fifth year of implementation that this study of the variations in positivity within the NCSP was undertaken. The purpose of this study was to examine variation in positivity within the English NCSP during 2007/2008.

MATERIALS AND METHODS

The NCSP dataset collects information on the number of screening tests, it is not a random sample of the general population. The prevalence of infection cannot be ascertained from the detected positivity because positivity was restricted to those tested, and coverage of the target population was low (4.9%).2–4 Consequently, positivity was used as the study outcome measure. The population coverage was low compared to the rates of 39% and 50% achieved among sexually active women in the Chlamydia Screening Pilots5 and, as a result, the sample may not be representative of all young people at risk of genital chlamydial infection.

For each screen, a core dataset of 12 variables was collected which comprised: clinic code, patient number, gender, date of birth, postcode (zip) of patient residence, ethnicity, attendance date, reason for test, specimen type, new sex partner in last 3 months, 2 or more sex partners in last 12 months, type of laboratory test, and test result.1 From this information, the following variables were included in the analysis: age, gender, ethnicity, whether the person had had a new sex partner in the past 3 months, and whether the person had had 2 or more sex partners in the past 12 months. Screening setting, which was attributed from the clinic code and implementation phase, which was assigned using the PCO of the screening venue, were also included. The 2 questions relating to sexual behavior were closely related to the inclusion criteria of the screening programme (see Introduction), which consequently limits interpretation of the behavioral data.

Variation in positivity by PCO according to screening volume was explored using funnel plots. Means were calculated and 2-sided standard errors used to distinguish unusually high and low positivity rates. Two methods of logistic regression were used to explore the risks associated with a positive screen: single variable and multivariable logistic regression and multilevel logistic regression. The referent groups for the calculation of odds ratios (ORs) were allocated separately for each variable and were: age, 16; white ethnicity; general practitioner (GP); having a new sexual partner within the last 3 months; and having 2 or more sexual partners within the past 12 months. Data for men and women were analyzed separately using STATA 8.2.6 Interactions were investigated and the smallest adequate model fitted. The multilevel logistic regression model was used to explore the analysis further. This had a 2 level hierarchy; the first included implementation phase, with the remaining variables included at the second level. There was little difference between the coefficients produced by this and the multivariable logistic regression so the results of the single and multivariable logistic regression analyses were reported.

RESULTS

A total of 370,012 screening tests were reported. After excluding the records of attenders for whom either gender was unknown, (922) test results were incomplete (10,642), or who were of ineligible age (23,546), 334,902 were available for analysis, 29% of which were in men.

Variations in Screening Volume and Positivity by PCO–Funnel Plots

Overall positivity was 7.6% in men and 9.3% in women. Funnel plots show that substantial variation exists in positivity detected within individual PCOs. Fewer screens were done in men and there were a substantial number of PCOs for which unusually higher or lower levels of positivity were seen (Fig. 1). In contrast, for women there was a largely consistent pattern with few PCOs falling outside 2 standard errors of the mean (Fig. 1).

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Figure 1.:
Funnel plots exploring the relationship between screening volume and positivity for PCOs participating in the NCSP: 2007/2008.

Regression Analysis-Men

For men, the multivariable analysis showed that risk of positivity increased rapidly to plateau from ages 19 (OR: 2.58; 95% CI: 2.25–2.97) to 24 (Table 1; Fig. 2). Risk of positivity was higher in young men of black Caribbean (OR: 1.57; 95% CI: 1.37–1.80), black background unspecified (OR: 1.61; 95% CI: 1.32–1.96), mixed (OR: 1.26; 95% CI: 1.08–1.47), and unknown (OR: 1.40; 95% CI: 1.21–1.61) ethnicity compared with whites. Risk of positivity amongst black African, Chinese, and other ethnic groups were the same as whites and all Asian groups were at lower risk although only 2.57% (2530) of men were of Asian ethnicity. When compared with attenders at GP, risk of positivity was higher for screening tests done in chlamydia screening offices, community contraceptive services (CCS) and youth clinics, whereas risk of positivity was lower in screening tests done at the military, educational settings and at “pee-in-the-pot” days (outreach events at which urine testing is offered to eligible attenders). Attenders at hospital, pharmacies, and prisons were at the same risk as attenders at GP. Multivariable analysis showed that, for men, risk of positivity varied significantly with age (P < 0.0001), ethnicity (P < 0.0001), clinical setting attended (P < 0.0001), whether the person had had a new sexual partner in the past 3 months (P < 0.0001), and whether the person had had 2 or more sexual partners in the past year (P < 0.0001). The risk of positivity detected in phases 2 and 3 was not significantly different from the baseline (P = 0.4122).

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TABLE 1:
Chlamydial Positivity Seen in Men Taking Part in the National Chlamydia Screening Programme: Year 5 (2007/2008)
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Figure 2.:
Positivity by age and gender, NCSP: year 5 (2007/2008).

Regression Analysis—Women

For women, the multivariable analysis showed that risk of positivity increased rapidly to peak in 18-year-olds (OR: 1.20; 95% CI: 1.12–1.27), but then declined with increasing age (Table 2; Fig. 2). Positivity then declined with increasing age. Women aged 21 were at the same risk of chlamydial infection as 16-year-olds, and those aged 22 to 24 were at lower risk than those aged 16. Risk of positivity was higher in young women of black Caribbean (OR: 1.37; 95% CI: 1.27–1.50), black background unspecified (OR: 1.31; 95% CI: 1.13–1.50), mixed (OR: 1.16; 95% CI: 1.07–1.25), and unknown (OR: 1.27; 95% CI: 1.21–1.32) ethnicity compared with whites. Risk of positivity amongst black African, Chinese, and other ethnic groups were the same as whites and all Asian groups were at lower risk, although only 5% (4473) of women were of Asian ethnicity. When compared with attenders at GP, higher risk of infection was seen in attenders at CCS, youth clinics, and prisons, whereas lower risk was seen in attenders at pharmacies, educational settings, and pee-in-the-pot days. Attenders at chlamydia screening offices, hospital, the military, termination of pregnancy clinics, and obstetrics and gynecology clinics were at the same risk as attenders at GP. Multivariable analysis showed that risk of positivity varied significantly with age (P < 0.0001), ethnicity (P < 0.0001), clinical setting attended (P < 0.0001), whether the person had had a new sexual partner in the past 3 months (P < 0.0001), whether the person had had 2 or more sexual partners in the past year (P < 0.0001). The risk of positivity detected in phases 2 and 3 was not significantly different from the baseline (P = 0.1748).

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TABLE 2:
Chlamydial Positivity Seen in Women Taking Part in the National Chlamydia Screening Programme: Year 5 (2007/2008)

DISCUSSION

This sample of over 330,000 screens from sexually active young people is the largest description of testing for Chlamydia trachomatis in healthcare and nonhealthcare settings outside genitourinary medicine clinics in England. The observed age distribution was similar to that seen in prevalence studies and a systematic review.7–9 For women, positivity peaked at 18 and then declined, whereas for men positivity plateaued from 19 to 24. The large dataset allowed a more detailed analysis of positivity within ethnic groups than previously published and revealed considerable heterogeneity between ethnic groups. Black Africans, Chinese, and other ethnic groups had the same risk as whites, whereas Asians had significantly lower positivity and black Caribbeans and those for whom black background was unspecified had significantly higher positivity. These variations indicate that local health service commissioners need to ensure that services are targeted effectively so that all sections of the population have equitable access to sexual health services. The 2 behavioral variables showed that although risk of positivity was associated with one or more new partnerships, there was a high positivity within those who did not fulfill these criteria. This indicates that the context of sexual behavior surrounding the epidemiology of genital chlamydial infection needs to be explored by a more detailed investigation.

In 2007/2008, a catalyst to the implementation of chlamydia screening at PCO level was the Department of Health Local Delivery Plan target of screening 15% of the resident population between the ages of 15 and 24 years. However, an unforeseen consequence of the target was that it acted as a disincentive to screen those at high risk of infection and did not include cases identified through partner notification. The variation in positivity observed between PCOs could reflect differences in local strategies used to set up opportunistic screening. For example, screening, lowest positivity for both men and women was observed in pee-in-the-pot days and educational outreach initiatives which reflects the fact that testing is often offered to students at the beginning of the academic year before the start of sexual mixing. Only 29% of screening tests were in men, although more men than women were identified through the NCSP as a result of partner notification. To improve access to screening for men, the NCSP launched the “Men too …” strategy in autumn 2007. This seeks to raise awareness of the importance of screening men, engage local NHS organizations to ensure equitable access and develop models of best practice.10 Local implementation strategies need to ensure that core health services such as CCS, young persons services, GP, and community pharmacies are appropriately used to offer screening. Targets for sexual health need to encompass quality measures in addition to testing activity.

Between the ages of 16 and 24, the proportion of the population that is sexually active expands from 46% to 96%.11 The high positivity detected by the NCSP reflects high chlamydial incidence and reinfection rates.11–13 Young people generally have more sexual partners, more concurrent partners, a higher proportion of short partnerships, and a higher frequency of partner change than older age groups.11,14,15 The disparity in the pattern of positivity between men and women by age may indicate the influence of sexual networks to the transmission of infection with younger women tending to have older partners.14 Biologic factors may also explain the higher infection rates such as lower concentration of protective chlamydial antibodies, and amongst women, younger gynecological age.16

By the age of 16, many women are infected with chlamydia and the associated morbidity affects reproductive health over many years. Targeting 16- to 17-year-olds effectively is crucial to the control of the chlamydial epidemic: 1 modeling study has suggested that annual screening for infection in men and women aged less than 20 years may be the most cost effective intervention strategy.17 This strongly supports the inclusion of STIs and HIV within the Personal, Social, and Health Education framework of the National Curriculum and, in 2008, this became a statutory requirement to be covered by all schools.18 Some healthcare providers have commented that reducing teenage pregnancy and preventing STIs have not been equivalently addressed.19 Certainly, since 2000, Local Authorities have focused resources on attaining the government targets set for teenage pregnancy. The introduction in 2008/2009 of joint local area agreements between health and local authorities will promote the integration of chlamydia screening with other areas of national policy to give concise, clear messages to young people concerning the development and maintenance of a healthy sexual lifestyle.

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