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With great interest, we have read the recent paper in STI on cost effectiveness for Chlamydia trachomatis screening by Honey et al.1 We concur with their conclusion that more data derived from clinical trials are needed for policy making, particularly when considering the evidence on the subsequent risk of pelvic inflammatory disease (PID) in women who test positive for Chlamydia trachomatis.
Our paper2 was included and discussed in this review. As our approach was rather complex, we note that some parts of our design and results may have been misinterpreted. Honey et al note that our study was focused on screening both men and women in general practice with an age range for evaluation of 15–64 years. Although this information is correct, it does not reflect that screening for women only was considered separately and that women older than 34 years were not included in the screening programme. This misinterpretation by Honey et al formed the basis for exclusion of our study from further systematic review.1
Our approach differs from others’ in that we investigate the cost effectiveness by employing a population based dynamic model (Monte Carlo simulation).2,3 This approach enables us to simulate the C trachomatis transmission, the impact of prevention measures on the C trachomatis incidence and prevalence, and the risk for C trachomatis infection in a population. As a result, indirect effects (for example, future partners of current partners) over a period of several years can be considered using rates of partner change, mixing patterns, and transmission probabilities. We chose to analyse the screening programme over a period of 10 years. In our baseline analysis we assessed screening of men and women aged 15–24 years. However, in the scenario analysis we evaluated several other screening strategies, including screening of women aged 15–24, 15–29, and 15–34 years.
Despite the restriction of C trachomatis screening to the age groups labelled as “young” women, an evaluation of the transmission dynamics of C trachomatis in the population as described by our dynamic model requires the inclusion of men and older women in the model. For example, it may well be that C trachomatis is transmitted from a young woman to a man, from this man to an older woman, etc. Such transmission chains may occur over a period of years and may involve men and women of all ages. So, to adequately evaluate screening of women aged 15–24, a model is required that considers all sexually active age groups. Based on a Dutch sex survey, the sexually active age groups in our model were restricted to men and women aged 15–64 years.
Application of our model to the Netherlands showed that screening women aged 15–24, 15–29, and 15–34 years over a period of 10 years would result in net cost savings to society. When including (excluding) indirect costs, cost savings were reached after 2.8 (3.8) years, 3.1 (4.3) years and 3.3 (5.0) years, respectively. This evaluation considered the costs of screening (polymerase chain reaction testing, azithromycin treatment, GP fee) and partner referral as well as direct (medical) savings as a result of averted health care and indirect savings as a result of averted productivity loss.
We think that our dynamic approach leads to more realistic assessments of cost effectiveness in this area as it appropriately considers the highly infectious character of C trachomatis. At this time, our approach is being used to evaluate the cost effectiveness of C trachomatis screening programmes in two other European countries.
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