For almost 100 years, disease intervention specialists (DIS) have worked to interrupt transmission of sexually transmitted infections (STIs) in the United States population.¹ Although DIS perform a wide range of important public health functions, a primary role is to ensure that recently diagnosed STI patients are treated, to identify the sex partners of these STI patients, and to facilitate testing and treatment of their partners.¹ Given that DIS activities can be time-consuming and labor-intensive,¹ studies of the impact, implementation costs, and cost-effectiveness of DIS activities are necessary to guide resource allocation decisions.

In 2024, Martin and colleagues published a systematic review of the effectiveness of partner services and other DIS-delivered interventions for HIV and STIs, finding evidence that DIS-delivered interventions can improve clinical outcomes among index patients and can improve population outcomes by testing and treating infected partners.² Although numerous studies have demonstrated the impact of DIS-delivered interventions,^2–7 relatively few studies have assessed their cost or cost-effectiveness. The purpose of this analysis was to conduct a systematic review of the economic outcomes of DIS-delivered interventions for STI prevention. Specific review questions were: 1) What are the program costs and cost effectiveness of DIS-delivered interventions for STIs including partner services in the United States? 2) How do these outcomes vary across geographic settings, intervention, and infection? Cost effectiveness was defined broadly to include cost utility analysis and cost benefit analysis.

We extended Martin et al.’s recent systematic review of the effectiveness of DIS-delivered interventions for HIV and STIs,² which followed the National Academy of Medicine⁸ and Patient Centered Outcomes Research Institute (PCORI) methods⁹ with a registered protocol.¹⁰ The methods and results of our economic evidence review follow the Preferred Reporting Systems for Systematic Reviews and Meta-analyses (PRISMA) reporting guidelines.¹¹ Our study did not undergo review by an institutional review board because it is a literature review. Deviations from the initial review of the effectiveness of DIS-delivered interventions are described below.

Our literature search started with the 1,915 unique records identified in Martin et al.’s DIS intervention effectiveness review,² which were located using a broad set of HIV, STIs, and tuberculosis search terms in PubMed/MEDLINE, CINAHL, ProQuest Dissertations & Theses Global, and Web of Science. To focus on economic outcomes, the 1,915 unique records identified in Martin et al.’s initial keyword search were first narrowed down to a subset of 295 records with one of the following words in the title or abstract: cost, affordable, budget, economic, or monetary; at this stage, an additional 42 records were removed due to a focus on tuberculosis, or being a conference abstract or duplicate (see Figure 1). The 253 records that underwent a first-round screening of the titles and abstracts used a hierarchical screening to exclude studies that did not meet criteria in the following order: economic analysis (cost, cost-effectiveness, or cost-benefit), United States setting, primary research, and DIS-delivered intervention including partner services. Thirty-four studies were subsequently assessed in a full-text review, which excluded studies based on the following hierarchical criteria: published before 2000, no STI-related outcomes reported, not a DIS-delivered intervention, or no economic outcomes reported. Additional studies were located based on hand-searching the references of all studies included in the initial review of intervention effectiveness and review articles located in the initial search.

Consistent with the prior program effectiveness review’s screening methods,² one author screened articles in the first stage (title and abstract) and two authors screened articles in the second stage (full-text review). Quality control methods used in the recent program effectiveness review were having each author involved with the screening double-code at least 30 studies with the first author, progressing articles with unclear determinations to the full-text review, regular team meetings to discuss decisions, and having a third author review studies without a consensus decision. Similar procedures were used in this review.

To compile relevant information from the included articles, a data extraction sheet (Supplement 1) was developed based on the economic evaluation abstraction form used by the Centers for Disease Control and Prevention Community Guide to systematically abstract data from economic evaluation studies.¹² The data extraction form was reduced in scope and refined through pilot testing and consultation with all study authors on how to tailor it for this review. Extracted information included a description of the intervention, infection(s), study setting and population, analytic methods and comparison interventions, perspective (such as societal or healthcare), currency year (such as 2019 US dollars), and key findings. Two authors (AM, HK) extracted data from the screened articles, with one performing the initial extraction and a second reviewing the completed extraction sheet to verify numbers. Discrepancies were resolved with the lead author and consultation with other authors.

Study designs were classified into four main categories consistent with the Community Guide’s data extraction sheet: cost analysis, cost-effectiveness analysis, cost-utility analysis, and cost-benefit analysis (Supplement 2). Cost analyses were defined as studies that assessed the overall cost of a program or the cost per service rendered, such as cost per index case assigned or the cost per index patient interviewed. Cost-effectiveness analyses were defined as those that estimated the cost per benefit obtained by the intervention. This category typically included studies that estimated the cost per partner notified of exposure, the cost per partner reached, the cost per infected person identified, the cost per partner brought to treatment, and the cost per case of pelvic inflammatory disease (PID) averted. Cost-utility analyses were defined in the same way as traditional cost-effectiveness analyses, except that outcomes were reported in terms of the cost per quality-adjusted life year (QALY) gained or another metric that incorporates quality of life. Cost-benefit analyses were those that assessed the net cost of a DIS intervention in terms of the cost of delivering the DIS services minus the medical costs saved by the DIS activities. For this review, only the relevant outcomes were extracted. For example, Gift et al., 2008¹³ reported results for seven scenarios with different combinations of screening and partner notification among women, men, or both women and men. Information extracted was limited to three analyses that allowed for a direct assessment of the economic outcomes for adding partner notification to a given screening strategy. If there were numerous intermediate outcomes, the outcomes furthest downstream were selected (e.g., treatment of patients was prioritized over testing patients, which was prioritized over interviewing patients).

A narrative synthesis was used to summarize key findings due to differences in the nature of the interventions studied and economic outcomes reported. All costs were updated to 2023 dollars using the all items Consumer Price Index for all urban consumers (CPI-U) for the U.S. city average.¹⁴ Each study was also assessed with a checklist on the completeness of reporting (Supplement 3). Although assessment of study design features such as whether adequate sensitivity analyses were performed could directly assess study rigor, this review focused on reporting completeness because common questions to assess study quality are subjective and the variability in study designs make it difficult to evaluate consistently. The following steps were used to develop the criteria used in the completeness of reporting checklist: reviewing common checklists for assessing the quality of economic analyses^15–17 and a checklist used in a recent systematic review of HIV and syphilis testing costs in low- and middle-income countries,¹⁸ identifying common elements that were in multiple checklists and that were related to completeness of reporting, refining the list of potential items to those that would be relevant to all seven included studies considering the variability in the methodologies used, and creating clear operational definitions of the checklist items to improve inter-rater reliability. Two authors (AM, HK) conducted the reporting completeness assessment, with one performing the initial assessment and a second verifying the decisions.

Table 1 summarizes the study characteristics. The earlier studies included in this review (published from 2001 through 2010) evaluated economic outcomes related to partner notification for either chlamydia^13,19 or syphilis.^20,21 The two chlamydia studies examined partner notification with different levels of screening.^13,19 One syphilis study compared partner notification with selective screening to selective screening alone²⁰ and the other compared partner notification to selective screening as different interventions.²¹ The more recent studies examined HIV/STI or STI partner services as a broader intervention, with two quantifying the cost effectiveness and cost of the program^22,23 and one examining the cost effectiveness and cost of a DIS-directed peer network strategy to identify and test persons at high risk for syphilis or HIV.²⁴ The study settings and populations were diverse: inmates in a Massachusetts correctional facility,¹⁹ a four-city study (Baltimore, Denver, San Francisco, and Seattle),¹³ New York State excluding New York City,²² Louisiana,²⁰ Houston,²¹ a three-county study in Washington State,²³ and North Carolina metropolitan areas.²⁴

Overall, the studies provide evidence that DIS-delivered interventions including STI partner services can be a cost-effective use of public health resources (Table 2). In some instances, such as adding partner notification to a chlamydia screening program in a correctional facility,¹⁹ the cost of these interventions can be completely offset by averted medical costs. Cost and cost-effectiveness estimates of DIS-delivered interventions can vary across geographic settings and under different epidemiologic conditions.

This systematic review detected seven studies published since 2000 that provided original data on the cost or cost-effectiveness of DIS-delivered interventions including partner services for STIs. Although these studies varied in design and scope, this body of evidence suggests three key findings.

The first key finding is that, overall, DIS-delivered interventions including partner services can achieve gains in health at a reasonable cost and might even be cost-saving, meaning that the DIS-delivered intervention pays for itself in averted medical costs. For example, Gift et al. (2006)¹⁹ found that adding partner notification to an existing chlamydia screening program for male inmates was almost but not quite cost-saving, even without considering the full scope of potential benefits, such as the benefits of secondary transmissions prevented through partner notification.

The second key finding is that the cost and cost-effectiveness estimates for similar interventions and infections can vary substantially across geographic location and under different epidemiologic conditions. For example, in the Silverman et al. 2019 study,²³ the cost per syphilis case assigned was roughly four times as high in Spokane County than in King County or Pierce County. The authors hypothesize that such differences might arise because a large share of syphilis cases in Spokane County occurs among heterosexual persons, including a sizeable contingent of suspected methamphetamine users, whereas in King and Pierce counties most cases are among men who have sex with men. As another example, as shown in the Reynolds et al. (2001) study,²¹ the cost of partner notification relative to selective screening for syphilis varied substantially by stage of syphilis (e.g., the cost per syphilis case detected by partner notification was higher for primary and secondary syphilis than for early latent syphilis), highlighting the importance of epidemiologic context.

The third key finding is that most studies examined intermediate outcomes, such as the cost per partner notified or the cost per infected person treated, without considering averted medical costs or other downstream benefits of treating STIs. Although these intermediate results are not as easy to interpret as traditional cost-effectiveness results, these studies nonetheless help to quantify the benefits of partner notification. However, differences in analytic method (e.g., whether offset medical costs are included) can make it difficult to compare findings across studies.

The study by Williams et al. (2022)²⁴ provided a detailed explanation of how to interpret their intermediate cost-effectiveness analysis in terms of a cost-benefit analysis. For example, they noted that even if they excluded the syphilis-related benefits of the intervention, the cost per new HIV infection identified by the intervention ($26,191 [$21,975 unadjusted for inflation]) was lower than the cost-saving threshold of $32,532 [$27,296 unadjusted] per HIV infection identified in a prior published mathematical modeling study by Farnham et al. (2012).²⁵ Thus, Williams et al. were able to conclude that the intervention was cost-saving without having to do complex modeling to estimate the number of HIV infections averted by the intervention or the lifetime medical costs saved by the intervention. The work by Farnham et al. (2012)²⁵ to identify cost-effectiveness and cost-saving thresholds for the cost per new HIV infection detected based on behavioral changes associated with awareness of HIV serostatus highlights the potential for similar work in the STI field to estimate these thresholds for intermediate DIS outcomes for STIs. For example, health economic studies could be conducted to develop conversion factors that allow intermediate cost-effectiveness results (such as $2,144 per syphilis patient brought to treatment in the Johnson et al. (2017) study²²) to be easily converted into cost per QALY results.

Even though DIS deliver important public health services and these services reflect a cost-effective use of public health resources, demands on DIS have increased in recent years due to larger caseloads because of higher STI rates.¹ Further, many DIS face challenges such as low pay, high staff turnover, morale, and safety concerns.^1,26 Becher and colleagues describe cost-effectiveness considerations of strategies to assess potential DIS retention strategies, noting that costs incurred to keep skilled DIS can be offset by avoiding the costs of having to hire and train new employees.²⁶

We faced several key challenges in conducting this literature review and summarizing the results of the included studies. First, the studies we reviewed are not easily comparable to one another. For example, one study estimated the cost per syphilis case detected by partner notification and another estimated the cost per QALY gained by partner notification for chlamydia.^13,21 Second, for many studies, it was difficult to determine the precise interventions being evaluated. This difficulty was heightened by changes in terminology used to describe DIS activities over time. This limitation was addressed in part by our inclusion criterion that the intervention had to be DIS-delivered, to avoid articles about partner notification or expedited partner therapy more generally when not delivered by DIS. This inclusion criterion helped to clarify the specific interventions being evaluated in the included studies but led to the exclusion of potentially relevant studies. For example, we excluded a modelling-based study of the cost-effectiveness of partner notification for chlamydia, because the study did not specifically assess DIS-delivered partner notification nor did it include DIS-specific costs.²⁷ Third, although we excluded studies published prior to 2000 with the goal of focusing on more recent studies, most of the studies included in our review were published in 2010 or earlier. Thus, the health economic data we reviewed are dated, highlighting the need for updated studies on the cost-effectiveness of DIS-delivered interventions. Similarly, we did not address potential publication bias.

In summary, despite limitations, our systematic literature review compiles useful data on the health economics of DIS activities for STI prevention and control, such as partner notification. The available evidence suggests that DIS-delivered interventions are a cost-effective use of public health resources. Economic evidence can be a useful supplement to impact evaluations to inform resource allocation decisions. However, additional studies are needed to update the existing body of evidence. For example, health economic modeling studies could help to promote future evaluations of DIS activities by facilitating the conversion of intermediate cost-effectiveness outcomes (e.g., cost per syphilis case identified and treated) into standard cost-effectiveness outcomes (e.g., cost per QALY gained). Another gap is to update the evidence with more recent data to reflect large shifts in morbidity, treatment, and prevention since the publication of the studies we reviewed, including but not limited to Food and Drug Administration approval of HIV pre-exposure prophylaxis in 2012,²⁸ increases in reported rates of STIs and congenital syphilis,^1,29,30 and the 2024 clinical guidelines on the use of doxycycline postexposure prophylaxis for bacterial STI prevention.²⁹ Another fruitful area of further research is assessing economic outcomes in a wider range of settings, particularly in smaller health departments with fewer resources.