Sexually Transmitted Diseases:
Measuring the Uptake and Impact of Chlamydia Screening Programs—Easier Said Than Done
Chow, Joan M. MPH, DrPH
From the California Department of Public Health, Center for Infectious Diseases, Division of Communicable Disease Control, Sexually Transmitted Disease Control Branch, Richmond, California
I am grateful to Drs. Heidi Bauer and Kyle Bernstein for their insightful comments.
Correspondence: Joan M. Chow, MPH, DrPH, Chief, Epidemiology Unit, Sexually Transmitted Disease Control Branch, California Department of Public Health, 850 Marina Bay Parkway, Bldg P, 2nd Floor, Richmond, CA 94804. E-mail: firstname.lastname@example.org.
Received for publication November 22, 2011, and accepted December 9, 2011.
The passage of the landmark United States (US) Patient Protection and Affordable Care Act (ACA) of 2010 has placed a new emphasis on prevention services, including increased access, coverage, and improved quality of care.1 In this legislation, chlamydia screening qualifies along with other preventive services (The Patient Protection and Affordable Care Act, P.H. 111-148, March 2010, §2,713) as an essential health service benefit by virtue of having an “A” rating (“strongly recommended”) from the US Preventive Services Task Force. However, along with this important commitment of public health resources comes accountability by demonstrating outcomes and results. It should not come as a surprise that in the current era of unprecedented government budget reductions, there is a compelling need for evidence-based prioritization and impact assessment. Funding agencies increasingly need health program data to show the impact of investment in preventive services, and chlamydia screening is no exception. However, measuring the population-level impact of chlamydia screening expansion in the US since the 1980s has been problematic; conflicting data on screening uptake, chlamydia burden, and adverse reproductive outcomes, including pelvic inflammatory disease (PID) and tubal factor infertility, have all been challenging to interpret, despite compelling epidemiologic evidence supporting intervention.
Public–Private Investment and Chlamydia Screening Uptake
Chlamydia screening of young women is a priority intervention to reduce untreated asymptomatic sequelae and reproductive health consequences and is considered one of the top 10 cost-effective clinical preventive services.2 Investment in this public health strategy has received broad support and increased investment since the late 1980s across public and private sector health programs. For example, federal funding of the Infertility Prevention Project to provide testing and monitor chlamydia prevalence in public sector family planning and sexually transmitted disease (STD) clinic populations has grown to $30 million in fiscal year 2011 (Centers for Disease Control and Prevention communication). Much of this investment has been in the purchase of chlamydia tests, as evidenced by the large growth in chlamydia testing; laboratory surveys show nearly doubling of volume among public and commercial laboratories from 1996 through 2007 and now is the most common STD test.3,4
However, it is not clear whether this increase in aggregate testing volume has resulted in more young women being screened for chlamydia on an annual basis, per national recommendations. The answer increasingly depends on who is doing the measurement and what is being measured. In commercial- and Medicaid-managed care plans, chlamydia screening has been a prevention priority; for more than 10 years, the Health Employer Disease and Information Set (HEDIS) chlamydia screening quality-of-care measure has been used to monitor plan adherence to national chlamydia screening recommendations, and reporting is now required for plan accreditation. While chlamydia HEDIS screening rates among sexually active young women show an increasing trend during this period, reaching 45% and 61% by 2007 in commercial and Medicaid plans, respectively, these levels may be underestimates attributable to the restrictive criteria for being counted in the measure.5 However, other analyses of screening uptake based on nearly 2 million women enrolled in commercial plans from 2002 through 2006 temper our skepticism with the HEDIS estimates and indicate a dishearteningly low level of screening at 10% per year.6 Can such levels of screening, if valid, have an impact on chlamydia prevalence and related adverse outcomes?
The Mis-Measure of Chlamydia Disease Trends
Identifying reliable outcome measures to measure the impact of chlamydia screening at any level remains elusive. Monitoring the burden of chlamydial infections has been conducted most frequently with case report surveillance data. Almost universally in the US, chlamydia case rates have been increasing locally and nationally since reporting was initiated in the late 1980s.7 However, it has been difficult to interpret case-based trends in the context of concurrent increases in testing and more sensitive diagnostic tests. If case report trends cannot tell us about the impact of screening on population-level chlamydia burden, are there other more meaningful measures of impact?
Chlamydia prevalence monitoring of populations accessing care and getting tested within sentinel clinic settings, such as family planning clinics, STD clinics, and juvenile detention facilities, as well as nonclinical settings, has been promoted as an alternative measure.8 However, sentinel prevalence trends have also been difficult to interpret, due in part to inconsistent clinic participation, changes in client populations served and risk behaviors, and increasing screening uptake.8 Most Infertility Prevention Project regions have experienced little change in prevalence during the past 5 to 10 years, but in Region X in the northwestern US, the area with the longest history of prevalence monitoring, trends have been incrementally increasing.9 Clarity is slowly emerging, though, in the analysis of prevalence trends in programs with consistent population profiles and screening coverage levels. Federally funded National Job Training Program data among low-income adolescent and young adult participants show that prevalence has been declining.10 A key question is whether any of these declining prevalence trends are generalizable to the larger US target population.
In this issue, a new population-level perspective is offered by the Datta and colleagues analysis of population-based trends in chlamydia positivity based on testing of participants in 5 two-year cycles of the National Health and Nutrition Examination Survey (NHANES) during 1999 through 2008.11 We would expect that using a nationally representative household-based sample of the US population would address issues of selection bias and differential healthcare-seeking by gender that have limited interpretation of sentinel prevalence monitoring trends. In addition to finding higher prevalence among adolescents and young adults and among non-Hispanic black persons, consistent with prior observed patterns, the authors reported encouraging declines: 40% reduction in prevalence among all participants, 48% reduction among adolescents, and 45% reduction among non-Hispanic black adolescents. What was not expected were the gender-specific trends: a perplexing lack of reduction among the target screening population of women aged 14 to 25 years and a 53% reduction among males for whom only limited screening is recommended.
Although the authors declined to offer scenarios for why the NHANES chlamydia trends differ so radically from expected trends for females versus males, a few theories come to mind that have been offered previously to explain chlamydia case-reporting trends. Brunham and colleagues were the first to offer the “arrested immunity” hypothesis to explain increases in chlamydia case reporting in Vancouver after years of observed declines. The theory hypothesizes that relatively frequent annual screening plus treatment of otherwise asymptomatic infections among young women actually increases the number susceptible to reinfection as a result of reduction in time to develop immunity.12,13 By contrast, males are not subject to routine screening, and observed reductions in male chlamydia prevalence may also be attributable to increased treatment of partners of female cases identified through more frequent screening; expedited partner treatment options, including patient-delivered partner therapy, pharmacy-based pick-up, and field-delivered therapy, could further decrease asymptomatic infection that would otherwise persist. One limitation of the analysis was the inability to examine differential trends by gender, age, and race/ethnicity, especially in smaller NHANES subgroups; the sample should be powered adequately in future cycles to provide not only more reliable estimates but also to enable analysis of other socio-demographic and risk behaviors, including sexual network proxies.
The PID Measurement Dilemma: How Much Is There and How Much Are We Preventing?
In addition to the debate over measuring more immediate outcomes associated with chlamydia screening programs, another debate has emerged over measuring long-term outcomes, such as PID associated with untreated chlamydial infection. Efforts to replicate the landmark randomized controlled trial of chlamydia screening14 and prevention of PID have been rare and usually involved small-scale15 and/or underpowered trials suggesting less than definitive results on a population-level, such as the recent Prevention of Pelvic Infection trial.16 More formal efforts to implement PID surveillance have been problematic and unreliable, attributable to the poor sensitivity and specificity of clinical case definitions and lack of reporting requirements; only 20 states have instituted surveillance for PID, but the validity of these efforts is as yet unknown. Transition from inpatient to outpatient management of PID during the past 20 years further introduces problems in the interpretation of declining trends based on hospital discharge databases.7 Fortunately, recent efforts to use administrative clinical encounter data offer another promising option for monitoring PID, using data from women accessing care in private sector-managed care plans across the US.17,18 These analyses have shown encouraging decreases of 25% in PID diagnoses from 2001 through 2006 and correlated increases in chlamydia screening rates in this same population.
In this issue, Scholes and colleagues reported 10-year trends in screening and PID rates from 1997 through 2007 among Group Health Cooperative health plan enrollees in the northwestern US, the same setting that was included in the original trial of chlamydia screening and reduce PID incidence.19 While the analysis revealed expected increases in screening rates for all women of reproductive age, especially among the target group of young women, there was no significant change in chlamydia prevalence, and there was a dramatic 43% decline in PID rates. Encouragingly, the steepest declines in PID rates were among females aged 15 to 24 years, the segment of the plan population with the highest screening rates. Males also had higher rates of screening, as well as diagnoses of urethritis, but, in general, chlamydia burden was of at least an order of magnitude smaller than that of women and potentially reflecting a secondary effect of treated infections among women. The strengths of the analysis included a large sample that was representative of the health plan members with stable enrollment over the study period (similar to the NHANES study period) and use of standardized code sets for clinical, laboratory, and pharmacy services, so that health care utilization could be comprehensively characterized. Although these administrative data lack sexual risk behavior data to further explore underlying trends that may explain the dramatic PID declines, the potential to develop clinical scenarios and proxies should be considered a promising alternative.20 The bonus offered by this analysis over previous surveillance and administrative data analyses is that the three factors essential for evaluating chlamydia screening efforts, that is, screening uptake, prevalence, and PID, were all measured in the same population and measured to maximize reliability and validity. The availability of these data from one population thus starts to address many of the gaps and flaws encountered when interpreting imperfect measurements of uptake and impact.
Conclusions: The Promise of Better Measures
Meaningful evaluation of the impact of chlamydia screening requires thoughtful measurement of health care service utilization and disease outcomes, all elusive goals, as we have seen. We are now on the brink of leveraging significant health care systems changes mandated through the ACA to collect more representative and complete data linking interventions such as preventive services to outcomes through widespread adoption of electronic health records and commercial laboratory-based prevalence monitoring.21,22 The analyses presented by Datta and Scholes are important examples of how outcomes associated with chlamydia screening might be better measured and used to promote cost-effective control strategies, but it is clear that we will have the capacity to do even better. The expanded use of electronic health records in the coming years of ACA implementation will significantly improve our ability to say that health care programs are indeed doing a better job in expanding screening to young women and measuring a real impact on prevalence and preventable adverse reproductive outcomes: goals that benefit the whole community.
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