Using chlamydia positivity to estimate prevalence: evidence from the Chlamydia Screening Pilot in England

Studies have suggested that positivity can be used to estimate the prevalence of Chlamydia trachomatis in large-scale chlamydia screening programmes. A recent pilot of opportunistic screening in England estimated that the prevalence among 16–24-year-old women in Portsmouth and Wirral was 9.8% and 11.2%, respectively. This study assessed the continued validity of positivity as an approximate for prevalence. We re-analysed data from the Chlamydia Screening Pilot to estimate positivity, calculated as total positive tests divided by total tests, and compared these estimates with the previously reported prevalence, measured as the number of women testing positive divided by the total number of women screened. Overall positivity was 9.4% in Portsmouth and 11.0% in the Wirral; these estimates were not statistically different from prevalence, regardless of health-care setting, age group or symptoms. We conclude that positivity can be used as a proxy for prevalence.

Opportunistic screening for genital chlamydial infection. I: acceptability of urine testing in primary and secondary healthcare settings

OBJECTIVES

To determine the acceptability of opportunistic screening for Chlamydia trachomatis in young people in a range of healthcare settings.

DESIGN

An opportunistic screening programme (1 September 1999 to 31 August 2000) using urine samples tested by ligase chain reaction (LCR). Data on uptake and testing were collected and in-depth interviews were used for programme evaluation.

SETTING

General practice, family planning, genitourinary medicine clinics, adolescent sexual health clinics, termination of pregnancy clinics, and women's services in hospitals (antenatal, colposcopy, gynaecology and infertility clinics) in two health authorities (Wirral and Portsmouth and South East Hampshire). Main participants: Sexually active women aged between 16 and 24 years attending healthcare settings for any reason.

MAIN OUTCOME MEASURES

Uptake data: proportion of women accepting a test by area, healthcare setting, and age; overall population coverage achieved in 1 year. Evaluation data: participants' attitudes and views towards opportunistic screening and urine testing.

RESULTS

Acceptance of testing by women (16-24 years) was 76% in Portsmouth and 84% in Wirral. Acceptance was lower in younger women (Portsmouth only) and varied by healthcare setting within each site. 50% of the target female population were screened in Portsmouth and 39% in Wirral. Both the opportunistic offer of screening and the method of screening were universally acceptable. Major factors influencing a decision to accept screening were the non-invasive nature of testing and treatment, desire to protect future fertility, and the experimental nature of the screening programme.

CONCLUSIONS

An opportunistic model of urine screening for chlamydial infection is a practical, universally acceptable method of screening.

Opportunistic screening for genital chlamydial infection. II: prevalence among healthcare attenders, outcome, and evaluation of positive cases

OBJECTIVES

To determine the prevalence and treatment outcomes among young women screened opportunistically for genital Chlamydia trachomatis and to evaluate the impact of screening in those participating.

DESIGN

An opportunistic screening programme (1 September 1999 to 31 August 2000) using urine samples, tested by ligase chain reaction (LCR). In-depth interviews were used for programme evaluation.

SETTING

Screening was offered in two health authorities at general practice, family planning, genitourinary medicine (GUM), adolescent sexual health, termination of pregnancy clinics and women's services in hospitals (antenatal, colposcopy, gynaecology and infertility clinics). Main participants: Sexually active women (16-24 years) attending for any reason.

MAIN OUTCOME MEASURES

Screening data: prevalence of infection by age and healthcare setting; proportion of positive patients attending for treatment. Evaluation data: participants' attitudes and views towards screening and follow up.

RESULTS

In total, 16 930 women (16-24 years) were screened. Prevalence was higher in younger women (16-20) than those aged 21-24 years and was highly variable at different healthcare settings (range 3.4%-17.6%). Prevalence was approximately 9% in general practice. The role of the project health advisers in managing results and coordinating treatment of positive individuals was essential; the vast majority of all positives were known to be treated. Women felt that screening was beneficial. Improving awareness and education about sexually transmitted infections is required to alleviate negative reactions associated with testing positive for infection.

CONCLUSIONS

Prevalence of infection outside GUM clinics is substantial and opportunistic screening using urine samples is an acceptable method of reaching individuals with infection who do not normally present at specialist clinics.

What is needed on a laboratory test request form?

In the development of a screening programme for genital tract Chlamydia trachomatis infection, a modified test request form was devised and used successfully both to request the test, to collect data and to inform patients. Our examination of the practicalities and ethical and confidentiality issues involved in making a request for a laboratory test to assist clinical diagnosis or management, resulted in the introduction of extra features that we had not previously seen used in the design of request forms. Coded response boxes can have adjacent questions attached as a perforated strip. Removal of this question strip leaves a completed form with no explicit sensitive data (figure 2). A detachable information sheet for patients can also be incorporated into the request form (figure 1). The design of a request form raises issues that do not appear to have been widely or formally debated.

Evaluation of near patient testing for Chlamydia trachomatis in a pregnancy termination service

AIM

To identify and evaluate advantages and disadvantages of a near patient test (NPT) for Chlamydia trachomatis, using Clearview Chlamydia MF (Unipath Ltd) in a British Pregnancy Advisory Service (BPAS) clinic.

METHOD

The improved Clearview Chlamydia MF test was used to test endocervical swabs from 400 women attending BPAS clinic for termination of pregnancy. The results were compared with Ligase Chain Reaction (LCR), using Polymerase Chain Reaction (PCR) as the arbiter.

RESULTS

Twenty-seven women tested positive by Clearview Chlamydia MF (24 confirmed by LCR) and 32 by LCR.

COMMENT

NPT has potential advantages in specific situations where a quick result is required for optimal management of those testing positive. However, the current technology available for detection of Chlamydial infection results in time constraints, which limited its benefits in this study, where there was a high throughput of clients. A significant number of cases were missed by Clearview Chlamydia MF, though the sensitivity found is within the ranges reported for various enzyme immunoassays (EIA) - currently the most commonly used testing method. The study confirmed the high positivity in those attending for termination, especially in under 25-year-olds.

Management of Chlamydia trachomatis in a women's hospital: a review of current practice

OBJECTIVE

To establish a measure of testing for Chlamydia trachomatis within the Liverpool Women's Hospital with a view to optimising both testing and management of infection.

DESIGN

Prospective observational study to review the outcome of Chlamydia testing and subsequent management of patients between September 1997 - September 1998.

RESULTS

It was observed that opportunities for detecting infection were missed and testing was undertaken predominantly for diagnostic purposes.

RECOMMENDATION

Consideration be given to a centralised system for overview of positive results linking with audit/education to reduce sequelae of Chlamydia within gynaecology.