Chlamydia continues to be the most prevalent bacterial sexually transmitted disease (STD) in the United States.1 It has been estimated that approximately 2.8 million cases occur each year.2 Overall, the highest reported rates occur among the 20- to 24-year-old group, but for women, the 15- to 19-year-old group have the highest.1 The majority of infections in women are asymptomatic, and these infections can progress to serious sequelae, such as pelvic inflammatory disease, ectopic pregnancy, tubal infertility, and chronic pelvic pain.3–5 In men, untreated chlamydia may cause serious and costly sequelae such as urethritis, epididymitis, proctitis, and Reiter's syndrome.6
The most recently published direct medical cost of acute chlamydial infections was estimated at $31 to $147 per case (adjusted for inflation to 2007 dollars).7 However, rapid changes in diagnostic testing technology and health delivery services warrant updating cost estimates. The direct medical cost of acute care is needed in determining lifetime costs of chlamydial infections and for routine economic impact assessments (cost-effectiveness and cost-benefit analyses) of chlamydia screening programs and interventions. These analyses are critical to health policy decision-making. Thus, our main objective was to estimate the direct cost of chlamydial infections from the most recent private insurance claims data available.
We used outpatient and prescription drug claims data from the MarketScan database (MarketScan Database, Thomson Reuters, Ann Arbor, MI) between 2003 and 2007. MarketScan is a weighted database that contains data on persons who have employment-based health insurance, and lists claims annually on more than 5 million insured persons from more than 100 payers, including large employers, health plans, and government and public organizations.8 The majority of the US population is enrolled in employer-sponsored private health plans and the database includes weights that enable projection of analyses of the data to be representative of all privately insured persons in the United States.8,9
Using International Classification of Diseases 9th revision codes (ICD-9), we identified claims for chlamydia diagnoses (codes 078.88, 079.88, 079.98, 099.41, and 099.50–099.59) in the database. We extracted claims for all outpatient visits for which chlamydia diagnoses were identified as the primary or secondary diagnosis, or both. We did not include inpatient claims in our study because we did not expect patients to be admitted solely for chlamydial infections. Including claims from inpatient admissions would also complicate our cost determination. We assumed that visits within 30 days from the initial visit were part of the same episode of infection, and also examined the effect of extending the time frame for the same episode to 45 and 60 days from the initial visit.
Using the Centers for Disease Control and Prevention STD treatment guidelines,10 we identified recommended drugs for the treatment of chlamydia listed by both generic and brand names: amoxicillin, azithromycin, doxycycline, erythromycin base, erythromycin ethylsuccinate, levofloxacin, and ofloxacin. From the MarketScan Database we identified the National Drug Codes together with the associated keys for both generic and branded formulations of the prescription drugs listed earlier. This list was used to identify National Drug Codes in the drug claims database. We linked claims for outpatient visits with chlamydia diagnoses to prescription drug claims with the assumption that prescription drugs received 7 days before through 30 days after the initial outpatient visit were associated with a given episode.
Costs associated with outpatient visits included the costs of diagnosis, testing procedure, and office visits paid by both enrollee and insurance plan. To ensure that costs for other diseases were not included, we used only costs of outpatient visits in which diagnoses were exclusively for chlamydial infections. By doing so, we excluded claims for visits for which the primary or secondary diagnosis code was for another disease, but we included them in estimating the number of episodes. We also calculated the average cost of visits that included nonchlamydial diagnoses. Drug costs included all prescription drug costs paid by both enrollee and insurance plan. Because not all outpatient visits could be linked to drug claims, we computed total cost per episode as the cost of outpatient care plus prescription drug cost where available. We then calculated total cost per episode exclusively for those who had drug claims. We analyzed diagnostic test claims using current procedural terminology codes for chlamydia screening (87110, 87270, 87320, 87490, 87491, 87810, 87800, 87801).11
We used a 2-sided t test to test for differences in average costs. We used the medical care component of the Consumer Price Index for All Urban Consumers12 to adjust all costs to 2007 US dollars. To calculate average costs per episode, we used the weights available in the database that were designed to make the database representative of the national employer-sponsored privately insured population under the age of 65 years.8
Less than 11% of all patients had more than one episode of chlamydia over the 5-year period examined; with the number of episodes per patient ranging from 1 to 6 for males and 1 to 7 for females. Estimated total number of enrollees diagnosed with chlamydia, number of outpatient visits, the number of episodes, and average costs estimates are presented in the Table 1. When we used 30-, 45-, and 60-day windows to define an episode, the total number of episodes decreased by less than 3% (37,635–36,763), and there was no significant difference in estimated costs. Consequently, the results presented in the rest of this report were based on a 30-day window.
There were a total of 7301 male patients with 8264 chlamydia visits, and 26,313 female patients with 31,078 chlamydia visits (see Table 1). The proportion of chlamydia visits that also included nonchlamydial diagnoses was significantly higher (P < 0.01) for females than males (21% vs. 18%). Thus, females had substantially higher number of visits and a proportionately higher number of visits that included nonchlamydial diagnoses. The differences (between males and females) found in our study were expected based on recommendations for annual chlamydia screening for women,13,14 and the fact that women may have other medical examinations such as Pap tests15 during their outpatient visits. Of the 90,846 claims that were identified from 2003 to 2007, approximately 18% (16,752) were claims for diagnostic tests. However, majority (over 66%) of the diagnostic test claims was for 87491 (DNA-amplified probe [nucleic acid amplified tests]).
Although a majority (>80%) of patients had prescription drug coverage, we found drug claims for less than 40% of patients with chlamydia (Table 1). The proportion of female patients with prescription drug coverage who had drug claims for chlamydia treatment was significantly higher (P < 0.01) than for males (39% vs. 34%).
Estimated average costs per episode of chlamydia (both outpatient visit and drug claims) were $115 and $107 for males and females, respectively. Average total cost per chlamydia episode were $99 (outpatient cost) and $36 (drug cost). Average cost of visits that also included nonchlamydial diagnoses was $122 (male, $123; female $121). We did not find drug claims for more than 60% of the outpatient claims. Thus our average total cost (outpatient plus drug) was $108 per episode for both males and females combined. When we estimated total cost per episode exclusively for those who had drug claims, the average overall total cost was $142 (male, $157; female, $141). There were no significant differences in our costs estimates between males and females. The average cost of diagnostic tests was $44. However, the average cost of 87491 (DNA amplified probe - nucleic acid amplified tests) was significantly higher ($48; P < 0.05) than all the other tests except 87801 (immunoassay with direct optical observation), which was $91.
Our estimated direct cost (for those who had drug claims) was similar to the high-end values found in previous estimates of the economic burden of chlamydia (after adjusting for inflation), which was also estimated using data from higher-cost treatment settings, such as among private health service providers.7
There are limitations in this study associated with the use of medical claims data to estimate incidence and average cost per episode. First, there is no definition for an episode based on visits. As a result, it is not possible to differentiate between follow-up visits for a particular episode and visits for a subsequent one, which eventually affects the cost and number of episodes estimated. We minimized the concern for the definition of an episode by confirming the robustness of our results when we used 3 definitions for an episode based on the days of visits and found no significant difference in the results. The second and major limitation is partly a result of the first; lack of a well-defined number of visits for each episode presents the challenge of finding the associated treatment costs (drug claims). As a result, we did not find drug treatment costs for the majority episodes. However, it is conceivable that, for privately insured individuals, most of the chlamydial infections diagnosed were treated. Therefore, our estimates for those who were treated (i.e., estimated total average cost exclusively for those who had drug claims) were more reasonable for estimating the direct cost of chlamydial infections. A third limitation is that the estimates are not representative of the entire US population because only data from the employer-sponsored privately insured population was analyzed. Finally, one major limitation is that diagnosis codes in claims data can be inaccurate for a variety of reasons, including clinician diagnostic and data entry errors.16,17 Chart review might make the identification of chlamydia cases, and the estimation of associated costs, more accurate.
Our estimates represent lower-bound estimates of the cost of chlamydial infection in these populations because we did not include other associated costs, such as intangible costs and productivity losses that may be about 50% of direct medical costs18,19; the expected cost of sequelae such as pelvic inflammatory disease, ectopic pregnancy, tubal infertility, and chronic pelvic pain3–5 in women and urethritis, epididymitis, proctitis, and Reiter's syndrome in men6; and the costs of HIV infections that are a result of the elevated transmission and acquisition of HIV due to chlamydial infections.20,21 Despite these inherent limitations, our study provides, to our knowledge, the first direct estimate that reflects the actual cost of providing medical care for chlamydial infections to the United States employer-sponsored privately insured population.
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