To explore the impact of assumptions about acquiring acute infection, we varied the incidence of infection (first, second, and third episodes) between 5% and 200% of the base case value (i.e., 6% per year). When the incidence of infection was greater than 50% of the base case (greater than 3% per year), urine-based NAAT was more effective and less expensive than no screening, and screening with the RIS test on a clinician-obtained specimen became increasingly cost effective. When the incidence of infection was less than 50% of the base case, no screening was the least costly and most effective strategy; at even lower incidence levels, screening with both urine-based NAAT and with the RIS test on a clinician-obtained sample was decreasingly cost effective because the additional QALYs gained were increasingly more costly compared with the next least costly alternative. However, provided the probability of acute infection was greater than 15% of the base case, screening with urine-based NAAT remained less than $10,000 per QALY compared with no screening.
The comparative value of urine-based NAAT screening versus RIS was most sensitive to the likelihood of loss to follow-up when a second visit was required. For example, if fewer than 50% of women with gonorrhea detected using urine-based NAATs returned for treatment, the RIS test on a clinician-obtained specimen dominated all other strategies. However, if 80% or more women with positive urine-based NAAT results returned for treatment, the incremental cost effectiveness ratio associated with RIS exceeded $50,000 per QALY (Fig. 2).
The choice between screening tests was also sensitive to their comparative performance and costs. For example, if the sensitivity of the Gram stain was increased above 75%, the Gram stain strategy cost under $3500 per QALY compared with urine-based NAAT. If the RIS test cost was halved, the RIS test on a clinician-obtained specimen dominated all other strategies as the least costly and most effective alternative. At twice the cost, that strategy cost under $25,000 per QALY compared with screening with urine-based NAAT.
Our results indicate that screening women aged 15 to 29 with urine-based NAAT provided cost savings to society compared with no screening over a wide range of assumptions. Provided that most infected women are notified and treated as test results become available, given the high sensitivity and ease of specimen collection for NAATs, these tests offer a robustly cost effective solution for targeted screening programs in previously hard-to-reach asymptomatic populations.
Alternatively, as point-of-care tests such as RIS become available, screening with these tests will also be cost effective over a wide range of plausible costs and test characteristics through improving the proportion of infected women who are treated. Specifically, compared with a base case that reflects current data, and in large part as a result of improvements related to immediate treatment, we found that screening eligible women aged 15 to 29 by the rapid test on a clinician-obtained vaginal specimen was always most effective, preventing the greatest number of PID cases. We based the RIS cost on the best available data and assumed that the RIS would have a higher list price than that of NAATs. However, charges to patients may ultimately be higher for NAATs. Our results suggest that as the RIS cost decreases relative to NAAT, the strategy becomes more cost effective relative to all other alternatives. Provided the annual incidence of gonorrhea was at least half the base case (i.e., 3%) RIS on a clinician-obtained vaginal specimen was also cost effective compared with many other preventive health interventions.
Although the estimates of cost effectiveness were not very sensitive to variation in selected model variables, the choice of optimal strategy was. The choice between different screening tests (NAAT vs. RIS vs. Gram stain) was most influenced by assumptions about the proportion of patients lost to follow-up after a positive NAAT, the probability of immediate on-site care after a positive RIS test, and the relative testing costs. Presumptive diagnosis of gonorrhea by microscopic examination of Gram-stained smears collected during a pelvic examination is cheap, quick, and easy to perform, and when examined by experienced personnel, has a high specificity. As a result of its low sensitivity in women, however (26–88%), it is generally reserved for settings with a relatively high prevalence of infection such as sexually transmitted disease clinics. Our results lend weight to this argument, suggesting that despite its clear advantages in terms of time and cost, in settings where the prevalence of infection is 6% or less, the Gram stain strategy is only optimal compared with NAAT and RIS if it has a test sensitivity of greater than 88%.
Screening programs in populations with a documented high prevalence of gonococcal infection such as military recruits, prison inmates and detainees, and high school students have been shown to be clinically beneficial and cost effective.92–99 The study by Mehta and colleagues is the only published study to date examining the cost effectiveness of providing gonorrhea and chlamydia screening services in a high-risk ED setting. Although our analysis differs in some respects, like Mehta et al., we found that urine-based NAAT screening of women in a similar age group, with similar disease prevalence, was a highly cost effective and often cost-saving strategy depending on the comparator.
Although the estimates of incidence in our base case analysis may not be representative of all inner-city EDs, our policy conclusions may be applicable to other venues where the provision of follow-up care is a significant barrier and sexually transmitted disease rates are high. For example, women entering community jails are at high risk for gonorrhea, but efforts to integrate screening with admission have not been feasible, in part because women are often released before test results are available. Strategies that permit point of care treatment in such settings would likely be attractive investments.
Our analysis has several limitations. There is still considerable uncertainty about the natural history of acute gonococcal infection. Persistent infection, a term used to specify continued infection despite antibiotic therapy,100 is often difficult to distinguish from reinfection. Therefore, whether serially positive tests represent persistent or repeat infections, how reinfection and persistence influence estimates of the mean duration of a gonococcal infection, and the observed prevalence of gonococcal PID are areas of much clinical debate and key sources of uncertainty. The epidemiology of PID is further complicated by the fact that it is often asymptomatic and caused by pathogens other than Neisseria gonorrhoeae. Our choice of a state transition model (generally used to represent complicated chronic diseases in which the risk of clinical events changes over time) rather than a transmission model was a purposeful tradeoff made to more fully capture the costs and consequences associated with the long-term sequelae of gonococcal infection. Our analysis therefore does not consider transmission to sexual partners and newborns, the impact of partner notification, averted male sequelae, and the potential of enhanced transmission of HIV. Inclusion of these parameters, however, would likely increase the numbers of infected individuals and thus the costs and clinical consequences of untreated gonorrhea, thereby improving the case for screening.
Several other assumptions used in this article should also be acknowledged. For this model, we choose to use the performance characteristics of Gram stain of endocervical secretions as one standard for comparison. We acknowledge that Gram stain is not likely to be used for gonorrhea screening in most urgent care settings. Nonetheless, unlike RIS, or, to a lesser degree, NAAT, gram stain is a familiar, inexpensive, widely available rapid test for gonorrhea diagnosis that serves as a useful comparator that may be appropriate in other high-risk settings. Because many studies have explored the technique in which clinicians obtain vaginal swabs but do not use speculums, we also modeled clinician-obtained vaginal swabs to reflect the available data. However, given data from a number of recent studies comparing clinician-obtained vaginal swabs with patient-collected swabs, which suggest similar results, we presume that implementation of opportunistic sexually transmitted disease screening in an inner-city ED would use patient-collected swabs rather than specimens collected by clinicians. Finally, motivated by recent evidence of pools of undetected gonorrhea among some inner-city populations, our analysis conservatively focused on screening only for gonorrhea in high-risk ED settings. We recognize that coinfection with Chlamydia trachomatis will occur in some patients and would represent an additional potential benefit of a screening program. Therefore, our analysis likely underestimates the effectiveness and cost effectiveness of opportunistic screening. Although consideration of cotherapy or diagnostic tests that would provide test results for both N. gonorrhoeae and C. trachomatis would add complexity to the model and complicate interpretation of these results, this will be an important priority for future work.
U.S. gonorrhea rates have leveled off in the past few years, suggesting that testing in new settings should augment the current focus of gonorrhea control in sexually transmitted disease clinics, high schools, and prisons. Gonorrhea control efforts are made more urgent by the growing problem of antibiotic resistance to N. gonorrhoeae and recent prospective studies showing that treatment of sexually transmitted diseases can reduce incident cases of HIV.6–10,101 The introduction of powerful new gonorrhea test technologies coupled with a growing concern about scarce public health resources have led to a reevaluation of sexually transmitted disease screening practices in an effort to identify those most at risk of infection.102 The promise of a noninvasive rapid test that permits immediate treatment for gonorrhea, coupled with recent studies identifying adolescents and young adults attending EDs as high-prevalence populations5,22–30,103–105 and the results of this analysis all lend support to the emerging consensus that further declines in gonorrhea rates may require public health investments in new, high-prevalence settings such as EDs as the next critical frontier for sexually transmitted disease screening.26
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