The combination that saved the most money while preventing the most number of PID cases was endocervical NAAT screening of women + universal urine NAAT screening of men (Table 5). Although the screening costs for this strategy combination are higher than for other strategy combinations, the improved sensitivity and thus the cost savings due to PID prevention more than compensate for the increased screening costs. Table 5 also demonstrates that the combination of endocervical DNA probe screening of women + universal urine NAAT screening of men yields similar cost savings and PID prevention as the combination of endocervical NAAT screening of women + selective NAAT screening of men whose LE is positive. In other words, if it were necessary to reduce upfront screening costs, then PID prevention and overall cost savings are similar whether one chooses the more sensitive (but more expensive) test to screen women and the less sensitive (but less expensive) test to screen men or one chooses the more sensitive (more expensive) test to screen men and the less sensitive (less expensive) test to screen women.
This economic analysis of chlamydia screening strategies for sexually active students entering a national job training program has demonstrated that universal NAAT screening of female and male students upon training program entry was not only cost-effective, but also cost saving. For women, endocervical NAAT screening prevented 23 cases of PID and saved $27,000 as compared with DNA Probe screening. For men, universal NAAT screening prevented 21 cases of PID in past, present, and future partners and saved $16,000, when compared with selective NAAT screening of LE positive students. To ensure that only sexually active students are screened for chlamydia, information about sexual history will need to be included in the screening health history that students complete at their nursing admission.
Several previous studies with different populations of women have demonstrated the cost-effectiveness of annual NAAT-based chlamydia screening.11,26–32 However, only a few comparable studies have been conducted for men, and these have reported conflicting results.27,33–35 Furthermore, only 1 other study has evaluated the cost-effectiveness of simultaneously screening women and men.27 The current study goes 1 step further by directly comparing the cost-effectiveness of female screening to male screening via various strategy combinations. To our knowledge, this is the first study to do so.
When we directly compared the cost-effectiveness of female screening strategies to male screening strategies, our results demonstrated that the incremental number of PID cases prevented by choosing the more sensitive chlamydia test to screen male students was potentially equivalent to the incremental number of PID cases prevented by choosing the more sensitive chlamydia test to screen female students. The reason for this counterintuitive finding is because when a male infection is detected and treated, it potentially averts infection of (and PID in) multiple future female partners. Whereas, when a female infection is detected, only 1 case of PID is potentially averted, and only if she has not already developed silent PID before receiving treatment. While very worthwhile, screening and treating infected women is a secondary prevention strategy. In contrast, treating the reservoir of infected young men serves as a means of primary prevention for their future female sexual partners. Economic analyses that have not shown universal NAAT screening to be cost-effective in men did not take future partners into account.34,35
We have previously demonstrated in a male detention setting that screening all sexually active men for chlamydia upon admission is cost-effective, primarily due to the prevention of PID in future partners who will not be infected as a result of screening and treatment of the index male during detention.33 This point was recently highlighted by Fisman and Edmunds who used simulation studies to demonstrate that future transmissibility of an asymptomatic sexually transmitted infection is an important factor in determining whether asymptomatic screening is cost-effective.76 In their model, asymptomatic screening was not cost-effective when future transmissibility was not accounted for, but became increasingly more cost-effective with every generation of partners who avoided infection as a result of asymptomatic screening and treatment of the index case.76 Our study is limited by not using a dynamic model as Fisman and Edmunds did. Our model only accounts for the first generation of future partners; however, the job training programs are not closed systems with regard to sexual networks. Consequently, the mixing that occurs when a job-training student has intercourse with a nonjob-training student violates an assumption intrinsic to a dynamic model: with every generation screened in a closed system, the population prevalence will be reduced. To use a dynamic model, we would need to evaluate populationwide chlamydia screening beyond the job-training program.
As with any cost-effectiveness analysis, the results of this analysis are strongly influenced by the assumptions made and the parameter estimates used in the model. The parameter estimate most strongly driving the cost savings associated with male screening is the number of female sexual partners. Furthermore, the number of future sexual partners is more influential than the number of recent past or present sexual partners. Given that adolescents are known to engage in serial monogamy and concurrent partnerships, 39,77,78 it is reasonable to postulate that if the average young person reports 1.6 partners in the past 2 months, then he is likely to have an additional 1.6 partners in the future 2–12 months. The number of sexual partners reported in this study is consistent with previous estimates.27,39
The other parameter estimates driving the results were the NAAT testing fee, chlamydia transmission rate, LE sensitivity, probability of developing PID and cost of PID sequelae (which is related to probability of PID sequelae developing). NAAT processing fees are much more likely to drop than to rise given the greater degree of automation offered in each new generation of these tests. Chlamydia transmission rates reported in the literature57–59 are well above the threshold where selective NAAT screening became more cost saving than universal NAAT screening. Most studies have demonstrated an LE sensitivity of <80%.52 The 1 study that found an LE sensitivity of 80% was conducted with a sample size of only 10 chlamydia-positive participants.53
The final 2 parameter estimates driving the results of this study, probability of developing PID and cost and probability of developing PID sequelae, have been the subject of debate. Some authors have suggested that estimates used in CEAs have overestimated the true values of these parameters.66,79 van Valkengoed et al. concluded that the actual probability of clinical PID, ectopic pregnancy, and tubal factor infertility following a chlamydia infection are less than 1%.79 However, their estimates were based on medical register rates from Amsterdam, the Netherlands, which may not be generalizable to the United States. Additionally, they did not include subacute PID or chronic pelvic pain in the complication estimates because they assert that these 2 outcomes are not well documented.79
Rein et al. have estimated that the lifetime cost per case of PID and its sequelae ranges from $1105 to $1235 in 1998 dollars ($1275–$1424 in 2005 dollars).66 Rein’s estimate was also included in a natural history model developed by Yeh that follows a woman through a series of health transitions over time. Yeh concluded that the lifetime estimate of PID costs per woman lies between $1060 and $3180 in 2000 dollars ($1168–$3505 in 2005 dollars).10 However, Rein and Gift have asserted that 2 of the studies referenced by Yeh overestimated costs such that it may be more appropriate to use a narrower range of $1060–$1410 ($1168–$1554 in 2005 dollars).80 Our cost and probability estimates for development, treatment, and sequelae of PID sum to a lifetime PID cost estimate of $1730 in 2005 dollars, which is just above the revised range recommended by Rein and Gift, and our sensitivity analyses have demonstrated that even using the lower bound of $1168, NAAT screening remained the more cost saving strategy.
Perhaps the most compelling finding from our study is not how much money is saved or expended as a consequence of chlamydia screening but rather that use of a more expensive and more sensitive screening test in place of a less expensive, less sensitive screening test is just as cost-effective for male screening as for female screening, suggesting that NAAT based chlamydia screening of men is a judicious use of limited screening resources.
Our results have limited generalizability beyond a job training setting or perhaps a military setting because they assume a higher treatment rate (due to the residential nature of the national job training program) than is often achieved in the community. Yet, they are important because they demonstrate the feasibility, effectiveness, and cost-effectiveness of screening a population that is at particularly high risk for chlamydia infection. Furthermore, in analyses not reported, a subset of this same cohort reported that only 52% had a primary care provider, only 38% (46% of women and 30% of men) had been tested for an STD in the past year, and only 22% recalled being tested for chlamydia in the past year (Blake et al., unpublished data). This suggests that approximately two-thirds of the students would not otherwise have received chlamydia screening if they had not entered the job-training program.
The results reported in this study are based on a cohort of 4000 students entering New England job training centers annually. Nationally, 64,000 students enter job training centers annually, and recent national estimates for chlamydia prevalence in job training students suggest that the average male prevalence is 8.2% and average female prevalence is 15.8%.49,81 If the other parameter estimates used for this cohort are true for other parts of the country, then the National Job Training Program’s current policy of screening all entering job training students for chlamydia using a NAAT will prevent 704 annual cases of PID and save $688,000 when compared with the previous policy of DNA Probe chlamydia screening among women and LE screening among men.
In conclusion, universal NAAT screening of both female and male youth entering a national job training program offered the most cost-effective screening policy for preventing PID in these young women and in the recent past, present, and future female partners of these young men.
The pooled sensitivities were calculated for PACE2, LCx, and BDProbeTec by using the total number of infected participants for each test as the denominator and the total number of infections detected by the respective test as the numerator. Likewise, the pooled specificities were calculated by using the total number of uninfected participants for each test as the denominator and the total number of true negatives for each respective test as the numerator.
Eight thousand five hundred six women who were tested for chlamydia with endocervical PACE 2, 821 were infected (prevalence = 9.7%), and 565 were detected (sensitivity = 68.8%). Of the 7685 uninfected women, the PACE2 correctly identified 7669 (specificity = 99.8%). Two thousand six hundred eighty-two women were tested for chlamydia with endocervical BDProbeTec, 231 were infected (prevalence = 8.6%), and 216 were detected (sensitivity = 93.5%). Of the 2451 uninfected women, the BDProbeTec correctly identified 2425 (specificity = 98.9%). Fifteen thousand seven hundred twelve women were tested for chlamydia with a urine LCx, 1366 were infected (prevalence = 8.7%), and 1149 were detected (sensitivity = 84.1%). Of the 14,346 uninfected women, the LCx correctly identified 14,328 (specificity = 99.9%). Thousand nine hundred forty women were tested for chlamydia with a urine BDProbeTec, 183 were infected (prevalence = 9.4%), and 153 were detected (sensitivity = 83.6%). Of the 1757 uninfected women, the BDProbeTec correctly identified 1735 (specificity = 98.7%).
Sensitivity and specificity of the LCx and BDProbeTec were weighted to estimate the true chlamydia prevalence because each test was used for a portion of the prevalence study. The pooled sensitivity and specificity for each test were weighted according to how many participants were studied resulting in a sensitivity of 84.0% and a specificity of 99.7%.
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