An economic evaluation of a school-based sexually transmitted disease screening program Wang L Y, Burstein G R, Cohen D A

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1 An economic evaluation of a school-based sexually transmitted disease screening program Wang L Y, Burstein G R, Cohen D A Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology A school-based screening programme for sexually transmitted diseases (STDs) was compared with a non-school-based screening programme. Screening was specifically aimed at chlamydia and a urine-based ligase chain reaction (LCR) test was used. Type of intervention Screening. Economic study type Cost-effectiveness analysis. Study population The patient population was not explicitly stated, but it appears to have comprised male and female students between 9th and 12th grade. The study was not confined to those at high risk. Setting The setting was the community. The economic study was conducted in public senior high schools in New Orleans, USA. Dates to which data relate The effectiveness data related to material published between 1991 and Resource use was obtained from a study that took place between 1995 and 1998, and which was published in 1999 and The price year was Source of effectiveness data The effectiveness data were derived from a review and synthesis of completed studies. These were augmented by estimates and assumptions made by the authors and relevant experts. Modelling A decision-analytic model was used to estimate the number of chlamydial infections that would occur given each of the two screening programmes. The model took the form of a decision tree that detailed the events leading to chlamydial infection. Outcomes assessed in the review Within the school-based scheme the outcomes assessed were prevalence, the sensitivity and specificity of the LCR test, the return rate of treatment, and the effectiveness of the treatment. Within the non-school-based scheme the outcomes assessed were: Page: 1 / 7

2 the probability of an uninfected student having STD symptoms; the probability of an infected student having STD symptoms; the probability of a symptomatic student having an off-site diagnostic evaluation; the probability of an asymptomatic student having an off-site screening; the sensitivity of an off-site chlamydia test; the specificity of an off-site chlamydia test; the return rate for treatment; and the effectiveness of the treatment. Study designs and other criteria for inclusion in the review The authors did not report that they carried out a systematic review of the literature. The inclusion and exclusion criteria were not given. One of the studies included in the review was described at length, with details of the objective, design and results. The authors reported that this study was included in the review because it provided the relevant information. The designs of other studies used to provide the data were not reported. Sources searched to identify primary studies Not reported. Criteria used to ensure the validity of primary studies Not reported. Methods used to judge relevance and validity, and for extracting data Not reported. Number of primary studies included Seven studies were included in the review. Methods of combining primary studies In some cases a narrative method was used to combine data from the studies. In the case of sensitivity and specificity information, a weighted average was calculated from the available information and was reported in the text. However, the results of this calculation did not appear to have been included in the model itself. In some cases the authors combined data by using different studies to establish a plausible range for the variable concerned. They then used their own judgement to select a base-case value within this range. Investigation of differences between primary studies Differences between primary studies were not reported. Results of the review Within the school-based scheme: the prevalence was 12.4% for females and 6.1% for males; Page: 2 / 7

3 the sensitivity of the urine-based LCR test was 89.0% for both females and males; the specificity of urine-based LCR test was 99.0% for both females and males; the return rate of treatment was 91.6% for females and 97.5% for males; and the effectiveness of the treatment was 96.5% for both females and males. Within the non-school-based scheme: the probability of an uninfected student having STD symptoms was 6.0% for females and 1.7% for males; the probability of an infected student having STD symptoms was 9.7% for females and 3.8% for males; the probability of a symptomatic student having an off-site diagnostic evaluation was 71.7% for females and 70.0% for males; the probability of an asymptomatic student having an off-site screening was 28.9% for females and 13.0% for males; the sensitivity of an off-site chlamydia test was 74.6% for both females and males; the specificity of an off-site chlamydia test was 99.0% for both females and males; the return rate for treatment was 80.0% for both females and males; and the effectiveness of the treatment was 96.5% for both females and males. Methods used to derive estimates of effectiveness Some authors' assumptions and expert opinions were used to supplement the estimates of effectiveness from the review. Estimates of effectiveness and key assumptions Expert opinion was used to inform the frequency of testing for chlamydia. The authors assumed that 50% of female partners (i.e. partners of males tested) were not screened at school, that 11.5% of these females were infected, and that there was a 60% probability of transmission between infected males and their female partners. Measure of benefits used in the economic analysis The number of cases of pelvic inflammatory disease (PID) prevented was used in the economic analysis. Direct costs The study focused on the costs of running the screening programme (managerial and field staff), the tests, the follow-up data, nurse counselling and medication. From this the average and total costs of screening, treatment, and screening and treatment together, were estimated. The average was an average per student. The authors provided information on the costs and quantities for these variables, then stated that the "values" were provided by the Louisiana State University Health Sciences Centre. It is not clear whether this statement referred to both the costs and quantities. It seems that some of the quantities were measured during a study that occurred between 1995 and 1998, to which the authors referred extensively. Some of the cost data were obtained from published literature. The costs of PID and its consequences were also taken from published material. The costs of testing and treating chlamydial infections off-site were estimated from published material. The costs were estimated from the perspective of the health care system. The costs were incurred over a 3-year period and should, therefore, have potentially been discounted. However, the authors did not report that discounting was carried out. The unit costs were reported separately from the quantities of resources used. The price year was Page: 3 / 7

4 Statistical analysis of costs No statistical analysis of the costs was carried out. Indirect Costs The indirect costs were not included. However, they were not relevant to the study since the study concerned schoolaged children who are not economically productive. Currency US dollars ($). Sensitivity analysis The following one-way sensitivity analyses were carried out: test sensitivity, 82-96%; female partners untested, 25-75%; transmission probability, 50-70%; probability of PID, 20-40%; PID treatment cost, $1,097 - $5,388; female prevalence, %; and male prevalence, %. A multivariate sensitivity analysis was used to estimate a worst-case and best-case scenario. Estimated benefits used in the economic analysis The number of cases of chlamydia infection expected in female students was 37.1 in the school-based scenario and in the non-school-based scenario. The number of cases of chlamydia infection expected in male students was 12.4 in the school-based scenario and 69.5 in the non-school-based scenario. The number of cases of chlamydia infection expected in female partners was 5.2 in the school-based scenario and 29.2 in the non-school-based scenario. The number of cases of PID expected was 12.7 in the school-based scenario and 50.7 in the non-school-based scenario. The total number of cases of chlamydia prevented by replacing the non-school-based screening with the school-based screening was The total number of cases of PID prevented by replacing the non-school-based screening with the school-based screening was Cost results The cost associated with testing for and treating chlamydial infections was $86,449 in the school-based scenario and $24,481 in the non-school-based scenario. Page: 4 / 7

5 The cost associated with testing for and treating PID was $40, in the school-based scenario and $159, in the non-school-based scenario. The cost prevented with treating PID and its consequences was $119, The net saving (net of the additional costs of screening) of replacing the non-school-based screening with the schoolbased screening was $57, Synthesis of costs and benefits The incremental cost-effectiveness ratio was reported to be -$1, This figure represents the cost (actually a saving, as the figure is negative) per PID case prevented. For four of the five one-way sensitivity analyses, the authors stated that the results "remain cost-saving over a reasonable range". The sensitivity analysis showed that the cost per PID case avoided was sensitive only to the estimated costs of treating PID and its consequences. When the cost of treating PID was lowered to $1097, the cost per case prevented by the school-based scenario was $540. The authors estimated that, in the worst-case scenario, it would cost $1869 to prevent a case of PID. Authors' conclusions The school-based screening programme reduced the prevalence of chlamydia and the occurrence of pelvic inflammatory disease (PID), and resulted in cost-savings to the health care system. CRD COMMENTARY - Selection of comparators A school-based screening programme for the detection of chlamydia was compared with a non-school-based programme. Current practice was for screening to take place in a non-school environment. The alternatives were appropriate for the stated objective. Validity of estimate of measure of effectiveness The efficacy data were taken from a review of published studies, although a systematic review of the literature was not reported to have been carried out. The authors appear to have used the data selectively. The majority of the efficacy information was obtained from one study, which was well described but was not critically appraised. This information was supplemented with data from other studies, authors' assumptions and expert opinion. The designs of the other published studies were not discussed. Some estimates from the primary studies were combined. In some cases the authors used available sources to define a plausible range for a variable, then selected the mid-point for a base-case analysis. Reasons for differences between the studies were not discussed, and no justification for using the mid-point was provided. The authors considered the impact of some differences between the primary studies through the use of a sensitivity analysis. Validity of estimate of measure of benefit The authors estimated the number of PID cases prevented using a model populated with data from published studies. This was a logical measure of benefit given the objective of the study. Validity of estimate of costs The costs were estimated from the perspective of the health care system, and the costs and the quantities were reported separately. The authors considered the costs of screening and treatment (including administrative costs), and also the Page: 5 / 7

6 costs and consequences of PID. These categories covered all relevant costs. The indirect costs were, appropriately, not included since the study population comprised school-aged children who are not economically productive. The authors found that the results were sensitive to the costs of PID only. The quantity estimates appear to have come from a single published source. No statistical analysis was conducted. The authors did not comment on the reliability of the quantity estimates. The unit costs were provided by a local university. Further details of the source were not given. The sensitivity analysis of the total cost, which used appropriate ranges, demonstrated the impact of cost changes on the results. Other issues The authors stated that, to their knowledge, this study was the first to assess the cost-effectiveness of a school-based STD screening programme. Therefore, they were unable to compare their results to other studies. The issue of generalisability was addressed by the authors, and sensitivity analyses helped to improve the generalisability of the study to alternative settings. The authors do not appear to have presented their results selectively. A number of limitations were discussed. These included the various sources from which estimates were taken, the fact that the possibility of reinfection was not considered, and the exclusion of the costs and benefits of preventing gonorrhoea. Implications of the study The authors recommend that "policy-makers routinely consider incorporating school-based STD screening programmes as part of an STD control strategy". They suggest that further work is need to improve estimates, such as the costs of treating cases of PID, and the probability of PID developing from an untreated chlamydial infection. Source of funding None stated. Bibliographic details Wang L Y, Burstein G R, Cohen D A. An economic evaluation of a school-based sexually transmitted disease screening program. Sexually Transmitted Diseases 2002; 29(12): PubMedID Other publications of related interest Cohen DA, Nsuami M, Etame RB, et al. A school-base chlamydia control program using DNA amplification technology. Pediatrics 1998;101:e1. Cohen DA, Nsuami M, Martin DH, Farley TA. Repeated school-based screening for sexually transmitted diseases: a feasible strategy for reaching adolescents. Pediatrics 1999;104: Indexing Status Subject indexing assigned by NLM MeSH Adolescent; Adult; Chlamydia Infections /diagnosis /economics /epidemiology /prevention & control; Cost-Benefit Analysis; Decision Trees; Female; Gonorrhea /diagnosis /economics /epidemiology /prevention & control; Humans; Louisiana /epidemiology; Male; Mass Screening /economics /standards; Pelvic Inflammatory Disease /diagnosis /economics /epidemiology /prevention & control; Prevalence; Retrospective Studies; School Health Services /economics; Sensitivity and Specificity AccessionNumber Page: 6 / 7

7 Powered by TCPDF ( Date bibliographic record published 30/09/2003 Date abstract record published 30/09/2003 Page: 7 / 7