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Public health issues

Screening Females

A considerable number of studies have assessed the cost effectiveness of screening for asymptomatic chlamydial infection in sexually active young women in preventing upper genital tract complicated infection. These studies have been usefully reviewed by Honey et al., 2003 using systematic economic evaluation criteria.

Randomised controlled trial

Honey et al., 2003 identified only one published randomised control trial of the effectiveness of screening women for asymptomatic C. trachomatis genital tract infection, a study by Scholes et al., 1996, in the USA. In this study, women aged 18 to 34 considered to be at high risk for disease were identified by means of a questionnaire. Eligible respondents were randomly assigned to undergo testing for C. trachomatis or to receive usual care. Both groups were followed for one year. There were 9 verified cases of pelvic inflammatory disease (PID) among the 1009 women in the screening group compared with 33 cases among the 1598 women receiving usual care (relative risk, 0.44; 95 percent confidence interval, 0.20 to 0.90). This trial is the strongest evidence yet that a strategy of identifying, testing, and treating women at increased risk for cervical chlamydial infection was associated with a reduced incidence of PID [Scholes et al., 1996].

Practical experience

In Glasgow, Scotland, the main chlamydia laboratory introduced the LCx^® assay in 1997 for testing specimens from general practitioners and from genitourinary medicine clinics. They reported their actual experience. Testing activity increased four and a half times between 1996-1997 and 1999-2000 and the detection rate rose from 4.8% to 7.8%; an additional 331 men and 844 were women diagnosed at a cost per additional diagnosis of about £162 (~$227) for men and £263 (~$368) for women. It was considered that substantial public health gains were likely to be achieved, both at individual and public health level [Scoular et al., 2001].

Economic models

Wang et al., 2003  constructed a decision based economic model to inform a screening programme based on eight schools in New Orleans. Cost-effectiveness of screening was measured as cost per case of PID  prevented. Under base-case assumptions, at an intervention cost of $86,449 the school-based screening program prevented an estimated 38 cases of PID, as well as $119,866 in treatment costs for PID and its sequelae, resulting in savings of $1524 per case  prevented. Limited sensitivity analysis was performed; the results remained cost-saving over a reasonable range of model parameter estimates and it was concluded that School-based screening programs of this type are likely to be a cost-effective use of public funds and can reduce the burden of STDs among adolescents in this setting [Wang et al., 2003].

Tao et al., 2003 developed a resource allocation model using data collected from 5078 visits by women to a publicly funded family planning clinic system in Philadelphia, USA. Their goal was to determine the optimal strategy for screening coverage, test selection, and treatment for infection in these women. The model incorporated the following age distributions: <20 years (27%), 20 to 24 years (30%), and >24 years (43%), with corresponding prevalences of C. trachomatis infection of 10.6%, 6.9%, and 2.3%, respectively. Two screening test assays (DNA probe and ligase chain reaction for cervical specimens) and two treatments (doxycycline and azithromycin) were investigated. At the baseline annual budget of $6 per visit, the strategy that maximized both the number of infected women cured and cost savings would be to screen all women with DNA probe and to treat all women with positive tests with azithromycin. This strategy would result in 183 women cured at a cost-savings of $140,176. As might be expected, sensitivity analysis showed that the total budget had a great impact on the optimal strategy. However it was considered that resource allocation models enable clinic managers operating with a fixed budget to identify a strategy that maximizes the number of asymptomatic women cured and cost savings where the clinic age distribution and age-specific prevalences are known [Tao et al., 2003].

Two studies found that screening all young sexually active women was not particularly cost effective. Thus, in Ontario, Canada, Goeree et al., 2002  used a decision analytic model to assess the cost effectiveness of seven different screening programmes over a ten year period. The programmes included the use of nucleic acid amplification technology on urine or cervical swab specimens. The move from selected swab-based testing to screening all cases cost $ 1873 per case of C. trachomatis infection averted. If this programme was expanded to include all Ontario women in the high risk ages 15 - 24 years the cost was $5990 per case averted. It was concluded that it is more costly but also more effective to screen and treat high risk women age 15 to 24 years for C. trachomatis infection rather than testing and screening symptomatic women only. In Amsterdam van Valkengoed et al., 2001 also used a decision analytic model to evaluate the potential cost effectiveness of screening inner city women for asymptomatic C. trachomatis infection using LCR in conjunction with mailed, home obtained urine specimens. [for a review of this approach see: community based approaches]. In the test population the prevalence of asymptomatic infection was 2.9%. Extensive sensitivity analysis was performed on the probability of sequelae, the percentage of preventable pelvic inflammatory disease and the discount rate.  The estimated net cost of curing one woman, aged 15-40 years, of a C. trachomatis infection was US$1210. To prevent one major outcome (PID, tubal factor infertility, ectopic pregnancy, chronic pelvic pain, or neonatal pneumonia), 479 women would have to be screened at a net cost of $15,800. Changing the probability of PID after chlamydial infection from 5% to 25% decreased the net cost per major outcome averted by 78%. The results were less sensitive to variations in estimates for other sequelae. The authors concluded that systematic screening of all women aged 15-40 years for asymptomatic C. trachomatis infections is not cost effective. Although the results of the analyses are sensitive to variation in the assumptions, the costs on this broad age range population exceeded the benefits [van Valkengoed et al., 2001]. [This does not preclude the possibility that home sample collected screening strategies focussed on the high risk age 15 - 24 year old women might be effective]. However two other studies by the same Dutch group came to rather different conclusions. [ Postma et al., 2001 concluded that treatment of male partners of positive asymptomatic women substantially lowered the net costs per major outcome averted to the point where implementation of  screening should be considered [Postma et al., 2001].  Welte et al., 2000, concerned at the static approach of decision analytic models, used a more dynamic population-based, stochastic simulation model. This had the advantage of addressing dynamic processes such as chlamydial transmission and the impact of screening programmes on incidence. Over the first 10 years, ligase chain reaction screening the urine of women aged 15 to 24 years visiting a general practitioner yielded potential savings of $ 492 or $ 1086 depending on whether indirect costs were excluded or included. [This study makes the important point that a screening strategy has to run a number of years before cost savings begin to be made].

Taken together these studies suggest that the major benefits of screening women for asymptomatic infection are in high risk populations (eg women seeking termination of pregnancy) or in sexually active women aged 18 - 24 years old.  Cost effectiveness of screening strategies differs markedly in different settings and needs to be considered against local factors. Nevertheless Honey et al., 2003 in their systematic review of the cost effectiveness of screening young asymptomatic women for genital chlamydial infection concluded that it is cost effective at likely prevalence levels, although more data are needed to validate some of the assumptions being used in economic models. The studies reviewed by Honey et al., 2003 are summarised in Table 1 below.

Table 1. Summary of cost effectiveness studies modified and updated from that of Honey et al., 2003.  The Drummond score is a metric by which Honey et al  evaluated the studies they reviewed, with the "best" trials having a maximum possible score of 20 points. NI means not included in Honey et al., 2003.

Contact Tracing and Sexual networks

Tracing and treating the sexual contacts of a patient with chlamydial genital tract infection has long been advocated as an effective method of identifying new infected individuals and preventing reinfection. Contact tracing data have been codified into sexual and social network theory. An interesting paper by Cabral et al., 2003 matched a sexual network derived from province wide contact tracing data for Manitoba, Canada with the isolation and genotyping of associated C. trachomatis. A high degree of concordance was found between transmission events, on the basis of molecular data, and proposed transmission events, on the basis of sexual network data. The gratifying close agreement between the molecular and epidemiologic data suggests that the use of routine contact tracing data is a valid approach for the construction of sexual networks [Cabral et al., 2003]. Similar results were obtained by Lyssen et al., 2004 using omp1 genotyping. However the latter considered that the improved epidemiological knowledge gained by genotyping in connection with sexual networks was of limited benefit, presumably because omp1 genotyping is insufficiently discriminatory.

[MEW] July 2004

NEXT: Effectiveness of partner notification

References

Cabral, T., Jolly, A. M. & Wylie, J. L. (2003). Chlamydia trachomatis omp1 genotypic diversity and concordance with sexual network data. Journal of Infectious Diseases 187, 279 - 286.

Catchpole, M., Robinson, A. & Temple, A. (2003). Chlamydia screening in the United Kingdom. Sexually Transmitted Infections 79, 3 - 4.

Genc, M. & Mardh, P. A. (1996). A cost-effectiveness analysis of screening and treatment for Chlamydia trachomatis infection in asymptomatic women. Annals of Internal Medicine 124, 1 - 7. Full article html [Spreadsheet-based Bayesian decision analysis model. No sensitivity analysis].

Goeree R, Jang D, Blackhouse G, Chong S, Mahony J, Sellors J, Foy A, Chernesky M. (2001). Cost-effectiveness of screening swab or urine specimens for Chlamydia trachomatis from young Canadian women in Ontario. Sex Transm Dis. 2001 Dec;28(12):701-9.

Honey, E., Augood, C., Templeton, A., Russell, I., Paavonen, J., Mardh, P. A., Stary, A. & Stray-Pedersen, B. (2003). Cost effectiveness of screening for Chlamydia trachomatis: a review of published studies. Sexually Transmitted Infections 78, 406 - 412. [Good Review].

Howell M. R., Gaydos, J. C., McKee, K. T. Jr., Quinn, T. C. & Gaydos, C. A. (1999). Control of Chlamydia trachomatis infections in female army recruits: cost-effective screening and treatment in training cohorts to prevent pelvic inflammatory disease. Sexually Transmitted Diseases 26, 519 - 526.

Howell, M. R., Quinn, T. C., Brathwaite, W. & Gaydos, C. A. (1998a). Screening women for Chlamydia trachomatis in family planning clinics: the cost-effectiveness of DNA amplification assays. Sexually Transmitted Diseases 25, 108 - 117. [LCR is cost effective in Maryland for preventing pelvic inflammatory disease].

Howell, M. R., Quinn, T. C. & Gaydos, C. A. (1998b) Screening for Chlamydia trachomatis in asymptomatic women attending family planning clinics. A cost-effectiveness analysis of three strategies. Annals of Internal Medicine 128, 277 - 284.

Lysen, M., Osterlund, A., Rubin, C. J., Persson, T., Persson, I. & Herrmann, B. (2004). Characterization of ompA genotypes by sequence analysis of DNA from all detected cases of Chlamydia trachomatis infections during 1 year of contact tracing in a Swedish County. Journal of Clinical Microbiology 42, 1641 - 1647.

Mangione-Smith R, O'Leary J, McGlynn EA. (1999). Health and cost-benefits of chlamydia screening in young women. Sex Transm Dis. 1999 Jul;26(6):309-16. Review.

Marrazzo, J. M., Celum, C. L., Hillis, S. D., Fine, D., DeLisle, S. & Handsfield, H. H. (1997). Performance and cost-effectiveness of selective screening criteria for Chlamydia trachomatis infection in women. Implications for a national Chlamydia control strategy. Sexually Transmitted Diseases 24, 131 - 141.

Marrazzo, J. M,, Handsfield, H. H. & Whittington, W. L. (2002). Predicting chlamydial and gonococcal cervical infection: implications for management of cervicitis. Obstetrics and Gynecology 100, 579 - 584.

Paavonen, J., Puolakkainen, M., Paukku, M. & Sintonen, H. (1998). Cost-benefit analysis of first-void urine Chlamydia trachomatis screening program. Obstetrics and Gynecology 92, 292 - 298. Full article (html)

Postma MJ, Welte R, van den Hoek JA, van Doornum GJ, Jager HC, Coutinho RA. (2001). Cost-effectiveness of partner pharmacotherapy in screening women for asymptomatic infection with Chlamydia trachomatis. Value Health. 2001 May-Jun;4(3):266-75.

Postma, M. J., Welte, R. & Morre, S. A. (2002). Cost-effectiveness of widespread screening for Chlamydia trachomatis. Expert Opinion in Pharmacotherapy 3, 1443 - 1450.

Scholes, D., Stergachis, A., Heidrich, F. E., Andrilla, H., Holmes, K. K. & Stamm, W. E. (1996). Prevention of pelvic inflammatory disease by screening for cervical chlamydial infection. New England Journal of Medicine 334, 1362 - 1366.

Scoular, A., McCartney, R., Kinn, S., Carr, S. & Walker, A. (2001). The 'real-world' impact of improved diagnostic techniques for Chlamydia trachomatis infection in Glasgow. Communicable Diseases and Public Health 4, 200 - 204.

Sellors, J. W., Pickard, L., Gafni, A., Goldsmith, C. H., Jang, D., Mahony, J. B. & Chernesky, M. A. (1992). Effectiveness and efficiency of selective vs universal screening for chlamydial infection in sexually active young women. Archives of  Internal Medicine 152, 1837 - 1844.

Tao G, Gift TL, Walsh CM, Irwin KL, Kassler WJ. (2002). Optimal resource allocation for curing Chlamydia trachomatis infection among asymptomatic women at clinics operating on a fixed budget. Sex Transm Dis. 2002 Nov;29(11):703-9.

van Valkengoed, I. G., Postma, M. J., Morre, S. A., van den Brule, A. J., Meijer, C. J., Bouter, L. M. & Boeke, A. J. (2001). Cost effectiveness analysis of a population based screening programme for asymptomatic Chlamydia trachomatis infections in women by means of home obtained urine specimens. Sex Transm Infect. 2001 Aug;77(4):276-82.

Wang, L. Y., Burstein, G. R. & Cohen, D. A. (2003). An economic evaluation of a school-based sexually transmitted disease screening program. Sexually Transmitted Diseases 29, 737 - 745.

Welte, R., Kretzschmar, M., Leidl, R., van den Hoek, A., Jager, J. C. & Postma, M. J. (2001). Cost-effectiveness of screening programs for Chlamydia trachomatis: a population-based dynamic approach. Sexually Transmitted Diseaes 27(9):518-29.

WHO Regional Office for Europe (1990). Annexes 1 and 2. Cost estimates of infections and of salpingitis due to C. trachomatis, based in Swedish figures. In: Guidelines for the prevention of genital chlamydial infections [Ed. Mardh, P. A.] pp 38 - 42. WHO collaborating centre for STD, Uppsala.

Wilson, J. S., Honey, E., Templeton, A., Paavonen, J., Mardh, P. A. & Stray-Pedersen, B. (2002). A systematic review of the prevalence of Chlamydia trachomatis among European women. Human Reproduction Update. 8, 385 - 94.