Enhanced enzyme immunoassay with negative-gray-zone testing compared to a single nucleic Acid amplification technique for community-based chlamydial screening of men.

We evaluated a low-cost diagnostic strategy for detecting Chlamydia trachomatis in a low-prevalence population. We used an amplified enzyme immunoassay (EIA) with a reduced-cutoff "negative gray zone" to identify reactive specimens for confirmation by a nucleic acid amplification test. As part of the Chlamydia Screening Studies project, men provided a first-pass urine specimen, which they returned by post for testing. We tested 1,003 specimens by IDEIA PCE EIA (Dako) and Cobas PCR (Roche). There were 32 (3.2%) true positive specimens according to a combined standard using an algorithm requiring concordant results from at least two independent tests. All of these were positive by Cobas PCR and 24 were confirmed to be positive by PCE EIA, including 2 that gave results in the negative gray zone. There were 971 true negative specimens, 2 of which were positive by Cobas PCR and 19 of which were initially inhibitory for PCR. The relative sensitivity, specificity, positive predictive value, and negative predictive value of PCE EIA with PCR confirmation were 75.0% (95% confidence interval [CI], 56.6 to 88.5%), 100% (95% CI, 99.7 to 100%), 100% (95% CI, 88.3 to 100%), and 99.2% (95% CI, 98.4 to 99.6%), respectively. The corresponding values for Cobas PCR were 100% (95% CI, 89.1 to 100%), 99.8% (95% CI, 99.3 to 100%), 94.1% (95% CI, 76.9 to 98.2%), and 100% (95% CI, 99.6 to 100%), respectively, with 1.9% (19/1003) of the samples being initially indeterminate. When the prevalence of C. trachomatis is low, the use of an amplified EIA on urine specimens, with confirmation of results in the negative gray zone by use of a nucleic acid amplification technique, is not suitable for screening asymptomatic men. In addition, positive nucleic acid amplification test results should be confirmed and an inhibition control should be used.

Coverage and uptake of systematic postal screening for genital Chlamydia trachomatis and prevalence of infection in the United Kingdom general population: cross sectional study.

OBJECTIVE: To measure the coverage and uptake of systematic postal screening for genital Chlamydia trachomatis and the prevalence of infection in the general population in the United Kingdom. To investigate factors associated with these measures. DESIGN: Cross sectional survey of people randomly selected from general practice registers. Invitation to provide a specimen collected at home. SETTING: England. PARTICIPANTS: 19,773 men and women aged 16-39 years invited to participate in screening. MAIN OUTCOME MEASURES: Coverage and uptake of screening; prevalence of chlamydia. RESULTS: Coverage of chlamydia screening was 73% and was lower in areas with a higher proportion of non-white residents. Uptake in 16-24 year olds was 31.5% and was lower in men, younger adults, and practices in disadvantaged areas. Overall prevalence of chlamydia was 2.8% (95%confidence interval 2.2% to 3.4%) in men and 3.6% (3.1% to 4.9%) in women, but it was higher in people younger than 25 years (men 5.1%; 4.0% to 6.3%; women 6.2%; 5.2% to 7.8%). Prevalence was higher in the subgroup of younger women who were harder to engage in screening. The strongest determinant of chlamydial infection was having one or more new sexual partners in the past year. CONCLUSIONS: Postal chlamydia screening was feasible, but coverage was incomplete and uptake was modest. Lower coverage of postal screening in areas with more non-white residents along with poorer uptake in more deprived areas and among women at higher risk of infection could mean that screening leads to wider inequalities in sexual health.