A fourth indirect estimate adjusted for reason for chlamydial testing (Table 2, EQ2). We developed this adjusted estimate because 2009 Washington IPP data indicated that test positivity varied based on reason for testing: 8% among symptomatic women, 30% among women tested as contacts to a partner with chlamydial infection, and 6% among screened women. All case reports in Washington include fields in which medical providers report the reason for STD testing using the above categories. Because reason for testing among women testing negative was only available for tests done through IPP, we calculated this adjusted estimate using only IPP data.
Finally, to use all available data and minimize the influence of our test positivity estimate on our screening coverage, we developed a combined direct-indirect estimate of screening coverage (Table 2, EQ3). This measure directly defined the number of tests performed to identify cases diagnosed through reporting laboratories and estimated the number of tests performed in nonreporting laboratories based on a weighted average of test positivity in laboratories that provided data for the analysis.
A total of 48,054 women aged 15 to 25 years were enrolled in Group Health in 2009. Of these women, 37,595 (78%) used services. Among users, 22,679 (60.3%; 95% confidence interval [CI], 59.8%–60.8%) had utilization or claims data that met HEDIS criteria defining them as sexually active. This estimate was almost identical to the estimate of 61.1% (95% CI, 56.5%–65.5%) derived using NSFG data.
Sentinel population screening coverage estimates among Group Health users and enrollees are presented in Table 4. Estimates varied from 34.2% to 44.5%. Screening coverage estimates for all enrollees were approximately 10 percentage points lower than estimates restricted to users (34.2%–34.8% vs.44.6%–44.5%). These estimates did not substantially vary based on whether NSFG data, HEDIS criteria, or a combination of both was used to define the size of the sexually active population.
Indirect estimates of chlamydial screening coverage varied from 46.4% to 68.7%, depending on the source of positivity data used to estimate the number of women tested. Among laboratories providing data, the highest prevalence of infection was observed in the population tested through IPP, and the screening coverage estimate based on IPP data (49.1%) was consequently lower than those based on other data sources. At the other extreme, the prevalence of infection among women tested through Group Health was only 4.5%, and the population screening coverage estimate derived using those data was the highest ofthe estimates we defined (68.7%). Adjusting the IPP estimate for reason for testing had little effect on our measure of screening coverage, decreasing the estimate based on the IPP positivity from 49.1% to 46.4%.
The direct-indirect estimate, which added a direct measure of the number of tests performed to identify 5812 (52%) of the 11,218 total cases of chlamydial infection reported in young women in Washington in 2009 (103,752 tests) to an indirect estimate of the number of tests performed to identify the remaining 48% of reported cases from unknown laboratories (105,113 tests), yielded a screening coverage estimate of 57.6%.
We found that HEDIS estimates of chlamydial screening coverage were substantially lower than indirect estimates calculated using data on the number of infections reported in Washington State and laboratory data on test positivity. Indirect estimates of screening coverage varied widely based on the source of data used to define test positivity. However, because we were able to obtain data from laboratories that diagnosed more than half of all chlamydial infections in young Washington State women, we believe that our direct-indirect estimate is the best measure of population-level screening coverage. The direct-indirect approach minimizes potential error by directly measuring the number of tests performed to identify a large proportion of all cases and derives positivity data from diverse sources, diminishing error resulting from the use of data gathered from a potentially nonrepresentative population served by a single laboratory. Based on this approach, we estimate that almost 58% of all sexually active women aged 15 to 25 years in Washington were tested for C. trachomatis in 2009, a number that exceeds most prior screening coverage estimates.10,17
That our indirect estimates of screening coverage were higher than most10 but not all14 past HEDIS estimates was surprising and encouraging. We had initially hypothesized that screening coverage in a well-organized health maintenance organization would be higher than that observed in the general population. Several factors may explain the disparity we found between our HEDIS and indirect estimates. First, screening may, in fact, be lower in Group Health than in the general population of Washington young women. Alternatively, HEDIS may underestimate screening because of its failure to include tests performed outside the health care plan for which no claim is submitted (i.e., if a woman is tested outside Group Health and no claim is submitted to that organization, the tested woman would be misclassified as untested). This issue merits further study. Healthcare Effectiveness Data and Information System may also underestimate screening coverage by overestimating the proportion of women who are sexually active, although the close agreement we observed between HEDIS and NSFG-based estimates of sexual activity suggests that this is not a large source of error. Finally, our indirect estimates of screening coverage may be too high. However, we believe that this final possibility is unlikely. Although surveillance data may underestimate the number of cases of chlamydial infection in the state, thereby leading to an underestimate of screening coverage, it seems unlikely that surveillance overestimates the number of chlamydial diagnoses. If chlamydia positivity in laboratories for which we had no data were considerably higher than in the laboratories included in our analysis, our estimates of screening coverage would be too high. However, even if one assumes that nonreporting laboratories had a positivity of 6.3%, the highest positivity we observed among reporting laboratories, our overall direct-indirect estimate of screening coverage would only decline from 58% to 52%.
Although data assessing HEDIS in other areas would be useful, our findings suggest that the HEDIS measure may not provide an accurate absolute measure of screening coverage, either for all of a plan’s enrollees or for the wider population. However, the problem the HEDIS measure was originally designed to address—the need for a common metric for assessing quality of care within and between managed care organizations—persists. The challenge is how to make the measure more accurate and how to balance sources of error that inflate screening coverage (e.g., the focus on users rather than all enrollees) with those that may diminish coverage estimates (e.g., failure to capture out-of-plan care). One approach to improving the accuracy of HEDIS might be to routinely calculate screening coverage estimates for both users and all enrollees. These 2 metrics would give a fuller picture of quality of care and would identify the extent to which high screening coverage in some instances may result from plans providing women no medical services at all.
Our results suggest that chlamydial screening coverage is likely higher than previously estimated and that the existing program has enjoyed substantial success, at least as measured by its reach into the population compared with other recommended screening procedures. Although published estimates have used varying age ranges, limiting their direct comparability to our findings, using the HEDIS method, CDC investigators estimated that 41.7% of sexually active US women aged 16 to 24 years were tested for C. trachomatis in 2007.10 More recent HEDIS data suggest that coverage is close to 50% among Medicaid enrollees, but only 43% among persons enrolled in commercial health plans.14 Of note, screening coverage achieved through what is sometimes termed “opportunistic screening”25 in Washington State seems to be substantially higher than that achieved in European nations with national chlamydial screening programs. Recent estimates suggest that 13% of young men and women in Sweden, 14.6% to 25.2% of young women in England, and 25% of sexually active young women in the Netherlands are tested for C. trachomatis annually.26–28 Chlamydial screening coverage among young women in Washington also seems to be comparable with screening coverage for several other commonly recommended preventive medical services, such as colonoscopy (50.2%), mammography (53.0%), and prostate exams (44.1%), although the percentage of women who receive Papanicolaou tests (78.3%) is higher than the percentage tested for chlamydial infection.29
Strengths of our study include our use of data from a large health maintenance organization and from several laboratories that, in aggregate, identified 52% of all cases of C. trachomatis in Washington during the study period; our ability to explore how different approaches to defining the sexually active population and estimating test positivity affect screening coverage estimates; and the use of data on the number of tests performed per woman to adjust for the fact that some women test for chlamydial infection more than once annually.
Our study also had several limitations. First, laboratory test positivity data used in the study may not have been representative of all laboratories in Washington State, and our estimates of screening coverage varied substantially based on the source of laboratory positivity data used. This finding highlights the importance of obtaining laboratory data from multiple sources when using indirect estimation. Second, we only calculated a HEDIS measure for Group Health, which may be not be representative of other large health care providers. Third, several of our estimates used national NSFG data to define the proportion of women aged 15 to 25 years who were sexually active. It is possible that young women in Washington State are more or less sexually active than women nationally. National Survey of Family Growth does not enroll a large-enough sample to create a precise state-specific estimate of sexual activity. However, within NSFG, there are no significant differences in levels of sexual activity among young women by region (G. Tao, personal communication, CDC). Finally, our findings may not be generalizable to other areas of the United States.
In summary, we found that the HEDIS measure of chlamydial screening may underestimate true population-level screening coverage and that indirect estimation using data collated from large laboratories is feasible and is probably the preferred method for estimating population-level screening coverage. Based on these findings, we believe that state and local health departments should work with large laboratories to obtain de-identified data to follow trends in chlamydial screening. Because laboratory data do not typically include demographic information such as race and ethnicity, additional efforts may be requiredto identify sectors of the population with low screening coverage.30 On the other hand, insofar as collection of laboratory data on chlamydial testing can be linked to acquisition of information on other tests (e.g., HIV and hepatitis C testing), the approach we propose has the further advantage of allowing health departments to monitor a variety of communicable diseases of public health significance.
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