SEXUALLY TRANSMITTED INFECTIONS (STIs) pose a substantial public health problem in the Russian Federation, especially in major cities.1–4 In the capital city of Moscow, with its 10.5 million population, the reported incidence rates of syphilis and gonorrhea in 2001 were 137 and 107 per 100,000 persons, respectively.5
Historically, the main focus of the national STI control program has been routine, compulsory STI screening of large sectors of the population, based on occupation.6–8 At its inception in 1920s, occupation-based screening was justified in part by the belief that STIs could be transmitted from infected workers to their large number of daily work-related contacts. Each year approximately 10 million people (roughly 7% of the population) are screened through these programs, which focus on syphilis and gonorrhea but sometimes include trichomoniasis, chlamydia, and HIV.
Despite the large number of people screened, few cases of STIs are detected through occupation-based screening. Further, the screening programs use STI diagnostic methods such as Gram stain for gonorrhea screening of both men and women and the Wasserman reaction (WR) test for syphilis that are less sensitive than more current screening tests.9–12 The evaluation of the costs and benefits of occupation-based screening would help decision makers to review the screening programs, policies, and diagnostic technologies to use limited resources more efficiently.
The main objectives of our study were 1) to determine the prevalence rates of syphilis and gonorrhea in the occupational groups, 2) to conduct a cost-effectiveness analysis of occupation-based screening, and 3) to recommend alternatives to the existing screening program.
Materials and Methods
Occupations subject to the occupational screening program can be generally classified into 4 main groups: (a) food handlers and other food industry workers, (b) market salespersons (e.g., vendors in indoor and outdoor markets such as produce stores and street vendors who sell items such as shoes, towels, clothes, etc.), (c) education and health care providers, and (d) hotel and other public utility workers. Between June 1 and October 31, 2001, study participants were recruited in a consecutive fashion until the sample size of 250 persons per each occupational group was reached. The total sample size of 1000 workers was determined based on the feasibility of the study and budget constraints. All participants gave oral consent for participation in the study. Under Centers for Disease Control and Prevention procedures for protecting human research participants, this project was determined not to constitute human subjects research and was exempted from Institutional Review Board.
Survey, Laboratory Methods, and Data Collection
Participants were surveyed and tested for syphilis and gonorrhea according to the currently implemented routine screening program in Moscow. The laboratory personnel collected venous blood for syphilis testing, and collected vaginal smears from women and urethral specimens from men for gonorrhea testing. For study purposes, serum samples were aliquoted into 2 specimens. The first was used as part of the screening program and the second was sent to the Federal Central Research Institute for Skin and Venereal Diseases (CRISVD) in Moscow for additional testing. As a part of the routine gonorrhea screening, vaginal and urethral specimens were tested using Gram stain.
From all the study participants, the interviewers collected sociodemographic data such as age, sex, place of residence and work, and occupation and first-catch urine samples that were then tested for gonorrhea at CRISVD using BDProbeTec ET amplification DNA assay (Becton Dickinson, Sparks, MD). For syphilis, the qualitative Rapid Plasma Reagin (RPR) test (Becton Dickinson) and Treponema pallidum Particle Agglutination Assay (TPPA) (Fujirebio, Malvern, PA) were performed at CRISVD. Syphilis was considered to be present when both these tests were positive. The stage of syphilis was not determined because of the limited capability of clinical examination of, and history taking from, the study participants.
We obtained Gram stain results for all the participants from the individual screening sites. Because of the logistic difficulties, we could not obtain results of the routinely performed laboratory screening for syphilis from the clinics and market sites. For the study purposes, we tested those serum samples that were positive by both RPR and TPPA with the nontreponemal serologic screening tests that are used routinely for syphilis in the Russian Federation. The tests included WR, which is a complement fixation reaction with the treponemal and cardiolipin antigens, and also the microprecipitation reaction (MR) with the cardiolipin antigen.
All the study participants were provided with the results of the routine syphilis (WR and MR) and gonorrhea (Gram stain) screening tests, and based on these test results, those with a diagnosed STI were treated appropriately.
Prevalence Data Analysis
We determined the prevalence of syphilis based on the results of RPR and TPPA and that of gonorrhea based on BDProbeTec ET results. We evaluated the performance of the syphilis screening tests routinely used in Moscow (WR and MR) by performing these tests on the serum samples that were reactive in both RPR and TPPA and by comparing the prevalence rates. We also evaluated the performance of the Gram stain compared with the BDProbeTec ET. We performed statistical analysis using Microsoft Excel 2000 software (Microsoft Corp., Redmond, WA) and SAS software, version 8.2 (SAS Institute, Cary, NC). We compared proportions using Fisher exact test. A 2-tailed P ≤0.05 was defined as statistically significant.
To examine the cost-effectiveness of screening occupational groups for syphilis and gonorrhea, we adapted decision analysis models (TreeAge software version 3.5.1, TreeAge, Williamstown, MA) developed by Kraut et al.13 (Figs. 1 and 2). We compared 4 options (no screening, screening for gonorrhea only, screening for syphilis only, and screening for gonorrhea and syphilis) for a hypothetical cohort of 1000 persons representing the occupational groups. For each option, we calculated the cost per STI treated successfully. We focused our analyses on syphilis and gonorrhea screening, as these 2 STIs are most commonly included in occupation-based screening programs.
Our analysis assumed a limited societal perspective and included all direct costs of the screening program and the direct medical care costs attributable to syphilis, gonorrhea, and their sequelae, regardless of who incurred these costs. We obtained cost and probability estimates from a range of published and unpublished sources as described in Tables 1 and 2. Costs were updated to 2003 rubles (and $2003).
We performed sensitivity analyses to determine how the results were affected by changes in the base case probabilities and costs used in the decision analysis. Specifically, we varied one or more of the following 5 sets of inputs, while holding all other parameter values at their base case values: (a) screening costs, (b) treatment costs, (c) probability of progression to sequelae, (d) STI prevalence, and (e) test performance (sensitivity and specificity).
A more detailed description of the cost-effectiveness analysis is available from the corresponding author upon request.
Characteristics of the Study Participants and STI Prevalence
Of the 1000 study participants screened in Moscow, 744 were women and 256 were men, with mean and median age of 43 years (range, 15–85 years). The mean age was 44.4 years (median, 45.0; range, 15–85) for women and 39.3 years (median, 37.5; range, 15–79) for men (P <0.01). More than 81.3% resided in Moscow City, 17.6% were from Moscow Oblast, and 1.1% from other regions. Occupational groups did not significantly differ about demographic characteristics.
The overall prevalence of syphilis based on the results of RPR and TPPA was 1.2% (12/997) (Table 3). Market salespersons had significantly higher prevalence of syphilis compared with the other 3 occupational groups combined [4.4% (11/248) vs. 0.1% (1/749), P <0.01]. Of the 12 syphilis seroreactive persons, 4 were women and 8 were men. Significantly higher prevalence of syphilis was observed in the age groups 19 to 24 and 25 to 29 years compared with those older than 45 years [3.9% (3/77) and 4.6% (4/87) vs. 0.2% (1/466), respectively; P = 0.01 and P <0.01, respectively]. The highest age- and sex-specific syphilis prevalence rates were observed in men aged 19 to 24 [9.5% (2/21)] and 25 to 29 years [10.3% (4/39)]. Of the 12 persons with positive test results from RPR and TPPA, 5 (41.7%) tested positive by both WR and MR.
In the routine screening sites, no gonorrhea cases were detected by Gram stain. However, based on BDProbeTec ET results, the prevalence of gonorrhea was 0.3% (3/990) overall, 0% (0/256) in men, and 0.4% (3/734) in women. The highest age-specific rate of gonorrhea was observed in 19- to 24-year-old participants [1.3% (1/78)]; no infection was detected in persons older than 45 years (P = 0.27).
Cost-effectiveness results are summarized in Table 4. The decision analysis model suggested that without screening 7.4 STI cases (syphilis and gonorrhea) would be successfully treated in a hypothetical cohort of 1000 women occupational group members, with a total cost (including sequelae cost of untreated or unsuccessfully treated cases) of 33,981 rubles ($1,019). Screening this hypothetical cohort would increase the number of STI cases successfully treated and would increase overall costs.
The incremental cost per STI case successfully treated (change in total cost divided by change in number of STI cases successfully treated) in women was 8409 rubles ($252) when moving from no screening to syphilis-only screening, and 20,179 rubles ($605) when moving from syphilis-only screening to combined gonorrhea and syphilis screening. For men, the results were similar, except that the incremental cost per STI case successfully treated when moving from syphilis-only screening to combined gonorrhea and syphilis screening was roughly twice that for women.
The results of the sensitivity analysis are presented in Table 5. The estimated cost-effectiveness of combined syphilis and gonorrhea screening was less sensitive to changes in the probability of sequelae than in changes to the other parameter values (screening and treatment costs, STI prevalence, and test performance). When applying a higher value for screening costs and for test sensitivity and specificity (a scenario consistent with the adoption of more expensive but better-performing diagnostic tests), the cost per STI case treated through combined syphilis and gonorrhea screening decreased substantially.
The relatively low STI prevalence in the screened groups and the poor performance of the diagnostic tests used were important factors in estimating the cost-effectiveness of occupation-based screening. Although the routinely screened occupational groups had low overall prevalence rates of syphilis and gonorrhea, syphilis prevalence was more pronounced in younger persons and in market salespersons. These findings suggest that prevention resources could be shifted from the occupation-based screening program (except perhaps for younger workers and market salespersons) and focused on higher risk populations such as youth, injecting drugs users, female sex workers, and homeless persons in whom high rates of syphilis and other sexually transmitted diseases have been reported.1,14–17
We found low performance of WR and MR tests compared with RPR and TPPA combination and of Gram stain compared with BDProbeTec ET amplification DNA assay in Moscow, a finding consistent with published data.9–12,18 Current national guidelines in the Russian Federation suggest the adoption of more current diagnostic tests,9,10,19 but such changes have been limited because of resource constraints. However, as indicated in the Sensitivity Analyses section, the cost of incorporating more current diagnostic tests can be offset by the improved sensitivity and specificity of these tests resulting in a lower cost per STI treated.
A transmission model could be applied to estimate the population-level impact of various screening strategies and their associated cost-effectiveness ratios. Such a model would require substantially more data (such as information about sexual mixing patterns) and resources than were available for this study.20 As a result, we used a static, decision analysis model to estimate the cost per case of STI treated in the screened population. Because the impact of screening and treatment on the interruption of STI transmission in the population was not addressed, the actual cost per STI case treated as a result of occupation-based screening could be lower than that we estimated (particularly for male screening). Although our model suggested that the cost per case of STI treated would be substantially lower if screening efforts were targeted at population with higher STI prevalence, our model is unable to estimate the population-level impacts of a shift in sexually transmitted disease prevention resources from the lower risk occupational groups to other higher risk population.
Limited information was available on the medical costs of STI diagnosis and treatment, and many of the parameter values we applied were based on assumptions and expert opinion. Furthermore, costs of diagnostic tests and treatment and medical staff salaries can vary greatly from clinic to clinic and depend on the type of health care facility. Uncertainty in the treatment costs impacted the estimated cost-effectiveness of screening only slightly for syphilis-only screening and rather substantially for combined syphilis and gonorrhea screening.
The sample size for each occupational group (250) was relatively small and may not be representative of the overall occupational group. However, with the possible exception of market salespersons, the syphilis and gonorrhea prevalence rates in the occupation groups suggested by the upper bound of the confidence intervals were substantially lower than the prevalence rates reported for high-risk groups such as injecting drugs users, female sex workers, and homeless persons in Moscow.
To our knowledge, this is the first study to examine the cost-effectiveness of routine STI screening in adults in the Russian Federation. Although more studies are needed to inform optimal STI control strategies, our analysis does suggest important initial steps. In summary, changes in occupation-based screening, such as a focus on higher risk population as well as the adoption of more current diagnostic technologies, could help to use available STI prevention resources more effectively. Given the limited public health resources to fight the continuing epidemics of STIs, including the substantial recent increases in sexually acquired HIV,21 there is an urgent need to implement cost-effective STI interventions.
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