Obstetrics & Gynecology:
Original Research: Lead Article
Cost-Effectiveness of Screening Strategies for Gonorrhea Among Females in Private Sector Care
Bernstein, Kyle T. PhD, ScM1,2; Mehta, Supriya D. PhD, MHS3; Rompalo, Anne M. MD, ScM4; Erbelding, Emily J. MD, MPH2,4
From the 1Department of Emergency Medicine, New York University School of Medicine, New York, New York; 2Sexually Transmitted Disease Program, Division of Health Promotion and Disease Prevention, Baltimore City Health Department, Baltimore, Maryland; 3Department of Emergency Medicine, Boston University, School of Medicine, Boston, Massachusetts; and 4Division of Infectious Diseases, Johns Hopkins School of Medicine, Baltimore, Maryland.
Corresponding author: Kyle Bernstein, ScM, PhD, Department of Emergency Medicine, NYU School of Medicine, 462 First Ave, 3rd Floor, Room A345, New York, NY 10016; e-mail: email@example.com.
OBJECTIVE: To identify the optimal screening algorithm for gonorrhea infection among females in private sector care, using cost-effectiveness analysis.
METHODS: We compared 6 strategies using decision analysis for urine nucleic acid amplification testing for gonorrhea testing in a theoretical cohort of 10,000 females aged 15–35 years: 1) screen women aged younger than 25 years; 2) screen women aged younger than 30 years; 3) screen women aged younger than 25 years who report any risk (pregnant, drug use, new sexual partner < 30 days); 4) screen women aged younger than 30 years who report any risk; 5) screen women aged younger than 25 years or those who report any risk; and 6) screen women aged younger than 30 years or those who report any risk. Infection prevalence and sensitivity and specificity were by direct observation from a retrospective cohort of females attending the Baltimore City Sexually Transmitted Disease Clinics between 1999 and 2002. The main outcome measures were untreated gonorrhea cases and their sequelae in women, transmission to a male partner, congenital outcomes, and cost to prevent a case.
RESULTS: Prevalence of gonorrhea was 3.0%. Not screening would result in 300 untreated cases. Not screening was cost-saving over all screening strategies. Strategy 6 resulted in the fewest cases of untreated infection (82), although Strategy 3 was the most cost-effective of the screening strategies. Univariate sensitivity analysis identified a threshold of 4.75% gonorrhea prevalence, more than which Strategy 3 became cost-saving over not screening.
CONCLUSION: Screening is recommended for females aged younger than 25 years with specific risks in populations with a gonorrhea prevalence of 4.75% or greater.
LEVEL OF EVIDENCE: II-2
In 2003, 335,104 cases of gonorrhea were reported to the Centers for Disease Control and Prevention (CDC), making it the second most frequent reportable disease after Chlamydia trachomatis.1 The estimated direct global costs for gonorrhea infections in the United States are in excess of $1 billion (in 1994 dollars).2 Several studies demonstrate that 30–80% of gonorrhea infections in women are asymptomatic,3–6 and thus go unreported.6–8 For example, in Baltimore, Maryland, where gonorrhea is hyperendemic, Turner et al8 reported that the estimated number of people with an asymptomatic, untreated gonorrhea infection exceeds the total number of diagnosed gonorrhea cases reported to the health department. Asymptomatic infections often lead to delays in treatment and in turn increase the risk of adverse reproductive sequelae such as pelvic inflammatory disease (PID) and ectopic pregnancy.9 Early identification and treatment of disease is a critical component of the promotion of reproductive health, particularly among women.
The CDC developed its first screening guidelines for Chlamydia trachomatis in 1985 and have since produced several revisions.10,11 The 2002 Sexually Transmitted Disease (STD) Treatment Guidelines recommend testing all sexually active women aged younger than 25 years, as well as older sexually active women with risk factors.12 Although gonorrhea screening often accompanies a Chlamydia trachomatis test, the CDC provides no guidance with respect to general or targeted screening for gonorrhea infection. In 2001, the CDC convened a panel of experts to address gaps in the prevention and control of gonorrhea in the United States. A major recommendation of this panel included “CDC should develop national screening guidelines to be used as a framework for the development of locally-appropriate screening criteria, and as guidance for areas or settings without local screening criteria.”.13
Although no structured guidelines are in place, gonorrhea screening has been implemented in several areas among diverse populations, usually in conjunction with Chlamydia trachomatis testing. Among adolescent women tested in family planning clinics, the prevalence of gonorrhea is estimated to be between 0.1% and 2.8%; 0–5.7% among adolescents tested at prenatal clinics; 1.6–8.5% at school-based clinics; and 0.6–12.4% in juvenile detention facilities.11 Several studies have examined the cost-effectiveness of implementing screening protocols for Chlamydia trachomatis and gonorrhea.14–16,17 In an emergency department setting, screening women for Chlamydia trachomatis and gonorrhea aged 18 to 31 years was cost-saving over not screening.18 Universal screening of women for Chlamydia trachomatis and gonorrhea was found to be cost-saving in a detention setting as well.19 The findings of these 2 studies that screening costs less than not screening (ie, screening is cost-saving) is uncommon; generally a proposed health intervention has a net positive cost. The cost-effectiveness of a proposed intervention is judged in relation to the cost-effectiveness of other interventions, or in relation to an established cost-effectiveness criterion for the expected health benefits.20
Most cost-effectiveness analyses examine Chlamydia trachomatis and gonorrhea screening algorithms in specialized sites of clinical services (ie, emergency departments, jails and prisons, STD clinics). We examined 6 gonorrhea screening strategies for implementation among women visiting private-sector clinicians using a medical cost and outcome decision model based on data from women attending the Baltimore City STD clinics between 1999 and 2002. Screening criteria based on age only and age and risk factors were compared with not screening. The goal of this analysis was to provide information to health care practitioners and medical decision makers as to how to potentially modify or implement a gonorrhea screening program for women in their clinic settings.
MATERIALS AND METHODS
All females aged 15–35 years who visited 1 of the 2 Baltimore City Health Department STD clinics between 1999 and 2002 and had a diagnostic test for gonorrhea performed were included in this analysis. As part of the standard clinical examination, symptom history, reason for visit, and risk behaviors were collected on standardized data collection forms and electronically captured. Women presumed or confirmed to be infected with gonorrhea were treated according to treatment guidelines current at the time of the visit.12,21 Women with culture-confirmed gonorrhea were compared with those who tested negative for gonorrhea infection to identify relevant risk factors. Characteristics examined included age, pregnancy, reason for visit, STD history, symptom history, drug use, number of sexual partners, exchanging sex for drugs or money, new sexual partners in past 30 days, and sexual partner with risk (known human immunodeficiency virus (HIV)–positive, bisexual, drug using).
Univariate statistics using χ2 compared women with and without gonorrhea infection (Table 1). Characteristics identified as statistically significant (P < .05) at the univariate level were included in a multivariate logistic regression model. The final logistic regression model was selected based on likelihood ratio statistics. Risks for gonorrhea infection identified in the final multivariate model were age less than 25 years, new sexual partner in the past 30 days, pregnancy, and drug use (Bernstein KT, Rompalo A, Olthoff G, Erbelding EJ. Suggestions for screening guidelines for Neisseria Gonorrhoeae infection. Presented at the National STD Prevention Conference, Philadelphia, Pennsylvania, March 8–11, 2004). Six screening criteria were created based on these factors. The sensitivity and specificity of the 6 screening criteria and their respective 95% confidence intervals were calculated. Analyses were conducted using SAS 8.2 (SAS Institute, Cary, NC). Use of these clinic data for this outcome was deemed exempt from review by both the institutional review board of the Johns Hopkins Medical Institutions.
The 6 decision branches of the tree represent the 6 screening strategies: Strategy 1 was to test all females aged younger than 25 years (standard CDC Chlamydia trachomatis recommendation); Strategy 2 tested all females aged younger than 30 years; Strategy 3 tested all females aged younger than 25 years who also reported any risk factor (defined as pregnant, new sexual partner in past 30 days, or self-reported drug use); Strategy 4 involved testing all females aged younger than 30 years who also reported any risk factor; Strategy 5 screened all females aged younger than 25 years or reported any risk factor; Strategy 6 included testing all who were aged younger than 30 years or reported any risk factor.
We used the number of cases of untreated gonorrhea infection and subsequent sequelae in women, episodes of transmission to sexual partners, congenital infections prevented per year, as well as prevention costs, as the outcomes considered in this cost-effectiveness analysis. Models were analyzed using TreeAge Pro 2005 (Treeage, Inc., Williamstown, MA), which calculated the probabilities associated with each Strategy on the basis of Bayes theorem. The analysis conducted here was limited to cases of gonorrhea that would occur in the female patient and her male sexual partner. The time horizon was a maximum of 10 years. A baseline discount rate of 3% was applied to sequelae costs that were expected to occur in the future.
The sequelae sequence and probabilities of outcomes from an untreated gonorrhea infection were derived from the literature (Table 2). Published reports show the probability of PID ranges from 10% to 40%.22–24 We assumed a 30% probability of PID in our base case analysis, 60% subclinical infection, and 15% inpatient treatment. For long-term sequelae, we included the probabilities of ectopic pregnancy, chronic pelvic pain, and tubal infertility. Additionally, we included the cost of transmission of infection to a male sexual partner, with subsequent urethritis and epididymitis; as well as congenital outcomes.
Published literature was reviewed, and the direct cost estimates used in this analysis are shown in Table 3. Treatment costs of PID, chronic pelvic pain, tubal infertility, and ectopic pregnancy were outcomes considered for untreated infections among women. Treatment costs for men included acute urethritis and epididymitis. Ectopic pregnancy was expected to occur 5 years after an untreated gonorrhea infection, 2 years to 5 years for chronic pelvic pain, and 7 to 10 years for tubal infertility.23,50 Sequelae that were expected to occur in the future were discounted at an annual rate of 3%.20 Minimum and maximum cost estimates (Table 3) take into account variations in sequelae incidence (Table 2). Indirect costs, such as days of work or school missed or infertility-related costs, were not included in this analysis.
All costs were adjusted to 2003 dollars using the medical care component of the Consumer Price Index for all urban users (United States Bureau of Labor and Statistics). The total costs of infection were derived from incidence and cost estimates. The expected cost of sequelae of 1 untreated infection in a woman was $821 (range $101 to $2,403), $3.36 in neonates (range $3.00 to $7.84), and $23.42 in males (range $5.44 to $117), for a total base case cost of $848 (range $109 to $2,528). Outcome of infection and associated costs were applied to a theoretical cohort of 10,000 women aged 15 to 35 years.
Programmatic costs included nucleic acid amplification testing (nucleic acid amplification testing), treatment, and adverse effects. This analysis was based on the assumption that gonorrhea screening would take place in the context of an existing medical visit. Therefore, the only substantial programmatic costs are related to diagnostic testing. The cost of urine nucleic acid amplification testingS testing was based on reimbursable cost estimates in Maryland (Table 3).54 The proportion of women returning for treatment was estimated at 80% based on local data. In addition to deriving estimated programmatic costs from the literature, we estimated programmatic costs from the Maryland Medical Assistance Program Physicians' Fee Schedule for outpatient care: adverse effects of antibiotics, cure of uncomplicated infection, outpatient PID and epididymitis treatment, and urethritis (Table 3).54 The choice of Current Procedural Terminology codes used to estimate programmatic costs was based on interview with several clinicians and the Clinical Director of the Baltimore City Health Department STD Clinics.
Table 1 describes the population used in this analysis. The prevalence of gonorrhea infection was 3% (95% confidence interval 2.7–3.2%). Compared with no screening, each of the 6 strategies would result in lower sequelae costs (Column B, Table 4) through greater numbers of identified and treated gonorrhea cases (Column D, Table 4). However, none of the screening strategies were cost-saving compared with not screening. Among the 6 strategies, the most selective strategy, Strategy 3, was the most cost-effective, with a cost of $535 for each additional treated case over no screening, whereas Strategy 6 resulted in the most treated cases.
One-way sensitivity analyses examined the minimums and maximums of cost estimates (Table 2). Enhanced screening became cost-saving over not screening only under 1 condition (Table 5): when the sequelae costs exceed $1342.60, Strategy 3 is cost-saving. By all other minimums and maximums, enhanced screening remained more costly than no screening, and Strategy 3 remained the most cost-effective of the enhanced screening strategies.
We then conducted a threshold analysis to identify other parameter variations that might affect the cost-effectiveness results. Strategy 3 became cost-saving over no screening when the prevalence of gonorrhea in the population exceeded 4.75% or when the cost of nucleic acid amplification testing testing was less than $26.50. When the probability of follow-up was 100% and the cost of treatment was reduced to zero, no screening remained less costly, and Strategy 3 remained the most cost-effective of the enhanced screening strategies. Even when the sensitivities of Strategies 1–4 were 100%, no screening was still the least costly option.
For multiway parameter analysis we estimated worst case and best case scenarios. For the worst-case scenario, model inputs (prevalence of infection, sensitivities and specificities of screening strategies, and costs) were maximized or minimized to favor not screening over screening; for best-case scenario results, inputs were varied to favor enhanced screening. Multiway parameter variation showed that routine gonorrhea screening could be as costly as $2,391 per additional case of gonorrhea treated (worst case scenario, Strategy 3), or save as much as $1,195 per additional case treated (best case scenario).
We compared 6 gonorrhea screening strategies and found none to be cost-saving over not screening at all. Among the 6 strategies examined, the most cost-effective was to screen all females aged younger than 25 years who report a new sexual partner in the past 30 days, drug use, or pregnancy (Strategy 3). No screening remained the lowest cost strategy when all parameters were varied to examine the upper and lower probability and cost estimates, except when sequelae costs exceeded $1,343. When the prevalence of gonorrhea was greater than 4.75%, Strategy 3 became cost-saving over not screening.
In this analysis we evaluated several gonorrhea screening strategies for women aged 15–35 years in a simulated private sector setting and found that none were cost-saving compared with no screening program. These findings are contrary to others,14–18 where in certain settings selective screening was shown to be cost-saving over not screening. Prior cost-effectiveness analyses have examined Chlamydia trachomatis and gonorrhea together and not gonorrhea alone.18,19,41,55 Given that the prevalence of Chlamydia trachomatis is significantly higher than that of gonorrhea,1 when these 2 outcomes are combined the prevalence of infection is higher. Corresponding averted sequelae costs are increased, becoming greater than programmatic costs (cost of assay, treatment, and clinician time). Further, cost-effectiveness analysis of gonorrhea screening in settings such as correctional facilities and emergency departments have a higher gonorrhea prevalence than in a private practice, which is what we estimate. We have found that selective gonorrhea screening became cost-saving when the prevalence of gonorrhea in the clinic population exceeds 4.75%. Although selective screening seems to be cost-saving in high prevalence populations, such as emergency department patients,59 the analysis presented here suggests that general population-based screening for gonorrhea may not be cost-saving.
Additionally, the choice of diagnostic test will impact final cost-effectiveness. A recent cost-effectiveness analysis examining gonorrhea screening in emergency departments found that point-of-care testing was significantly more cost-effective than urine based diagnostics, primarily by improving the proportion of infected women treated.59 However, in the analysis presented here, even when 100% of those gonorrhea positive were treated, no screening was still the least costly strategy, primarily because of the lower prevalence (3%) of gonorrhea modeled.
Although the screening strategies modeled here did not cost less than not screening (ie, they were not cost-saving), Strategy 3 led to a 30% reduction in untreated infections. The cost per additional infection treated was $535. Because there are limited data available on the effect of gonorrhea infection and sequelae on individuals' quality of life, the cost per quality-adjusted life year can not be calculated. The cost per quality-adjusted life year would allow direct comparison to the cost-effectiveness of other health interventions and also the conclusion as to whether the proposed strategy is “cost-effective” or “not cost-effective.”20
Screening coverage for Chlamydia trachomatis has improved dramatically over the past decade.1 The most recent 2002 STD Treatment Guidelines recommend all sexually active women aged younger than 25 years, as well as older sexually active women with risk factors, get tested for Chlamydia trachomatis.12 Although this analysis suggests that screening for gonorrhea among the general population of private care seekers is not cost-saving over not screening, the most cost-effective strategy was to screen women aged younger than 25 years who report a new sexual partner, pregnancy, or drug use. This strategy aligns well with the current CDC guidelines for Chlamydia trachomatis screening, which suggest screening all women aged 25 years and younger and older women with either new or multiple sex partners.12 Given the large increase in availability of molecular diagnostics for Chlamydia trachomatis screening12 and the ease in testing for both Chlamydia trachomatis and gonorrhea using the same nucleic acid amplification testing technology, often patients are tested for the presence of both infections. When a Chlamydia trachomatis diagnostic test is indicated, our findings suggest that gonorrhea testing may be more cost-effective if diagnostic testing is performed on a smaller subset of clients and not all females who meet the 2002 CDC Treatment guidelines for Chlamydia trachomatis screening. Prospective validation of risks for infection and the application of combining selective gonorrhea screening with Chlamydia trachomatis screening with subsequent cost-effectiveness analysis is necessary to confirm the cost-effectiveness. Although we modeled urine-based nucleic acid amplification testing screening, we have no reason to believe that nucleic acid amplification testing from cervical swabs would change the results presented here. When combined with a Chlamydia screening program, selective gonorrhea screening is likely to become more cost-effective, and the prevalence at which gonorrhea screening becomes cost-saving may be lowered.
Several limitations in this analysis merit discussion. First, data from the Baltimore City STD clinics were used to derive the gonorrhea prevalence estimates, as well as the 6 screening criteria examined. These data may not be representative of a general clinic population, which likely has a lower prevalence of gonorrhea infection and may have different risks for infection, or the risks identified in this analysis may have different sensitivities and specificities. However, few data regarding risk factors for infection are collected among the general population, making the examination of selective screening strategies for broader populations more difficult. As a result, our cost-effectiveness analysis is applied to a population of higher risk than would likely be seen in a general practice, which may have led to an overestimation of the cost-effectiveness of enhanced screening compared with no screening. Second, some costs and incidence of sequelae for Chlamydia trachomatis were used in this analysis. Considerably more information has been published examining the natural history of Chlamydia trachomatis. In cases where we were unable to identify published estimates of the probability or cost of an outcome for gonorrhea, the corresponding value for Chlamydia trachomatis was used. The effect of this on our results is unknown. Third, we evaluate these gonorrhea screening strategies with a static rather than dynamic model. We assume only 1 outcome per person, rather than the possibility of varying health states and reinfection. Additionally, we assume inpatient treatment for PID to be curative. Last, we did not include indirect costs in our analysis, such as days lost from work or school, which would have significantly increased the costs associated with an untreated case of gonorrhea. Therefore, had we used a dynamic model (which would incorporate the effects of reduced gonorrhea prevalence in subsequent transmission) and included indirect costs in this analysis, our results would have been more favorable to enhanced gonorrhea screening.60 Conversely, we did not model a programmatic cost of provider time to assess risk or collect a gonorrhea test specimen.
This analysis has limitations inherent in cost-effectiveness analyses, in that the conditional sequelae probabilities and costs are estimated from several sources, and uncertainty may not be fully addressed by the use of minimums and maximums. Results of our sensitivity analysis showed little deviation from the results of the base-case analysis in terms of relative effectiveness of strategies. This was due to the precise 95% confidence intervals on the sensitivity and specificity of the algorithms. These estimates are directly derived from our data, and the precision is a result of the large sample of women tested. Further, the sensitivities and specificities identified by our threshold analysis that would make the enhanced screening strategies dominant are likely unattainable.
Although several studies have examined the cost-effectiveness of screening for gonorrhea or Chlamydia trachomatis among higher risk populations, we have explored the usefulness of several screening strategies for gonorrhea among a population of lower-risk women seeking care. Our findings imply that screening for gonorrhea in a low-prevalence population may be cost-effective when applied selectively. Further, when the prevalence exceeds 4.75%, selective screening may be cost-saving. Additionally, the selective screening criteria found most cost-effective (screen women aged younger than 25 years who report drug use, pregnancy, or a new sexual partner) advocates testing a large subset of women who would be tested for Chlamydia trachomatis under the current CDC treatment guideline recommendations. Although more research is necessary to examine further the value of more generalized screening for gonorrhea, this study's results provide insight into the resource allocation of services and care among populations of women considered to be at a lower risk for gonorrhea infection.
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