Trichomoniasis is caused by the protozoan Trichomonas vaginalis and the annual incidence is estimated to be 174 million cases globally each year.1 In the United States, it has been estimated that over 7.4 million men and women are infected each year.2 However, reliable data on the prevalence of trichomoniasis are limited. Initial office visits for trichomoniasis in the United States have been estimated to be between 150,000 and 221,000 annually between 2001 and 2005, based on data from the National Disease and Therapeutic Index.3 The prevalence of trichomoniasis has been reported to be 3% to 48% in women in various studies.4 A population-based study using polymerase chain reaction for detection found an overall prevalence of 3.1%, or 2.3 million cases, in women aged 14 to 49 years, with significant variation by race or ethnicity and income.5
In women, trichomoniasis has been associated with vaginitis, pelvic inflammatory disease, preterm delivery, and cervical intraepithelial neoplasia.6–15 However, current epidemiologic understanding of trichomoniasis suggests that about a third of the cases may be asymptomatic.4,16 In men, trichomoniasis can cause nongonococcal urethritis, and if not treated, may result in complications such as epididymitis, prostatitis, and infertility.17 As in women, a large proportion of infections in men are asymptomatic.4,14,18 Trichomoniasis is also associated with elevated risk of acquiring other sexually transmitted diseases (STDs) and human immunodeficiency virus (HIV) and may double or triple the likelihood of HIV transmission.19–22 Research conducted decades ago reported a high transmission rate; of the infected women, 45% of their male partners were infected; of infected men, 100% of their female partners were infected.23–25 However, trichomoniasis is seldom detected in men4,14 because current diagnostic tests are insensitive or labeled for use with vaginal specimens only.4
Although trichomoniasis was first described as an STD decades before chlamydia and seems to be more common and causes similar sequelae, it has gained far less public health attention than chlamydia.16 Awareness of the economic burden imposed by trichomoniasis may help enhance the little attention it has had over the last decade. However, no study has directly determined the direct cost and economic burden of trichomoniasis in the United States. The most recent cost estimate for trichomoniasis was obtained by extrapolation from acute care visits for chlamydia and gonorrhea.26 Thus, the main objectives of our study were to estimate the average direct medical cost per episode and the annual incidence of trichomoniasis among the population of employer-sponsored women in the United States, and then determine the annual economic burden. To our knowledge, our study represents the first attempt to determine the economic burden of trichomoniasis among women, based on recent employer-sponsored private insurance data specific to trichomoniasis care. In addition to helping to assess the impact of the disease, accurate cost estimates are an indispensable variable in cost-effectiveness and cost-benefit analyses of program interventions and prevention activities.
Materials and Methods
We used outpatient and prescription drug claims data from the MarketScan database (MarketScan Database, The MEDSTAT Group Inc., Ann Arbor, MI) for 2001 through 2005. MarketScan is a weighted database that contains data on individuals who have employment-based health insurance and lists claims annually on over 5 million insured individuals from more than 100 payers, including large employers, health plans, and government and public organizations. Well over 50% of the US population are enrolled in employer sponsored private health plans, which enables projection of analyses of the data to be representative of all privately insured persons in the United States.27 Because most infections in men are asymptomatic,4,14,18 and the most widely used diagnostic tests are insensitive for testing men,4 our study focused on female patients only.
International Classification of Diseases, ninth Revision (ICD-9) codes for trichomoniasis diagnoses were used to identify female patients with trichomoniasis (131.00, 131.01, 131.02, 131.09, 131.8, and 131.9). Using these codes, we extracted claims for all outpatient visits in which trichomoniasis diagnoses were identified as the primary or secondary diagnosis, or both. We did not consider inpatient claims because we did not expect patients to be admitted for trichomoniasis as the main reason for inpatient admission. Records found in the inpatient claims database may be the result of other diseases diagnosed together with trichomoniasis, which would make cost determination difficult.
In a recent study, well over 90% of patients with treated episodes of trichomoniasis later tested negative within 2 weeks.28 On the basis of these findings, we assumed that outpatient visits within 30 days of the initial outpatient visit were part of the same episode of infection, because subsequent visits may have been follow-up care for more resistant infections. We repeated the analysis using 15 days instead of 30 days for follow-up visits for an episode to see whether the results would change substantially. Outpatient information was linked to drug claims based on the assumption that prescription drugs received 7 days before through 30 days after the initial outpatient visit were associated with a given episode of trichomoniasis.
From the CDC STD treatment guidelines,29 we identified metronidazole and tinidazole as recommended drugs for the treatment of trichomoniasis. From the MarketScan Database, we identified the National Drug Codes (NDCs) together with the associated keys for both generic and branded formulations of the prescription drugs listed above. This list was used to identify NDCs in the drug claims database (the list of NDCs used is available from the lead author).
To ensure that costs for other diseases were not included, we used only costs of outpatient claims in which diagnoses were exclusively for trichomoniasis. If the primary or secondary diagnosis code was for another disease, that particular outpatient claim was not included in our cost estimates, but was included in estimating the number of cases. Costs included costs paid by both the enrollee and insurance plan. Because not all outpatient visits had drug claims, total cost per episode was computed as the cost of outpatient care plus prescription drug cost where available.
Episodes and costs per episode were stratified by the following age categories: under 15, 15 to 24, 25 to 34, and 35 to 64 years. We used a 2-sided t test to test for differences in average costs and 2-sided z test for differences in proportion. The medical care component of the Consumer Price Index for All Urban Consumers30 was used to adjust all costs to 2005 US dollars. All cost estimates were weighted using the national weights available in the database. We extracted female annual enrollment information for each year and age category and used it to estimate annual incidence rates for claims per 100,000 female enrollees for the ranges presented above. Next, we estimated annual incidence rates using 5-year range age groups for women aged 15 to 49 to be able to compare it with the age distribution found in an earlier study,5 and the age distribution for other STDs in the 2006 surveillance report.3 We then extrapolated to the general US employer-sponsored private insurance population using the national weights. The estimated total annual cases and the estimated annual direct medical cost per case were used to calculate an estimated annual economic burden for the privately insured population. We also used the CDC Surveillance report annual estimate to determine the average annual economic burden.3 To do this, we calculated the average number of initial physician office visits for the years 2001 to 2005 and assumed that the age distribution of these visits matched the distribution of visits in the MarketScan database, adjusted for the US population.31 Finally, we used Current Procedures Terminology (CPT) codes to analyze potential diagnostic methodologies: wet mount (87,210), direct probe (87,660 and 87,797), and culture (87,070).
The total number of patients, number of outpatient visits, and number of episodes for trichomoniasis diagnoses by age category examined for 5 years are shown in Table 1. The number of episodes per patient and the number of outpatient visits per patient ever diagnosed with trichomoniasis are also presented. There were a total of 21,136 patients, having 25,383 outpatient visits for trichomoniasis over the 5-year period. Over 89% of women enrollees had prescription drug coverage. However, only about half (52%) had identifiable drug claims. Women younger than 15 years of age had the smallest proportion of drug claims (15%, significantly different from all other age categories, P < 0.01).
Average cost estimates per episode for outpatient care and prescription drugs and the total medical costs per episode of trichomoniasis by age category are presented in Table 1. Average outpatient and prescription drug cost per episode for all ages were $97 and $9, respectively. The total average cost per episode was $101. The total average cost per episode is lower than the sum of the average outpatient and drug costs because about 50% of the episodes did not have drug claims. Had we used cost data from only episodes for which we found drug treatment claims, our overall total cost per episode would have been approximately 10% higher ($111). Outpatient cost per episode for ages 15 to 24 was $120, which was significantly higher (P < 0.01) than all other categories. Also, average total cost per episode was significantly higher (P < 0.01) for age category 25 to 34.
The annual trichomoniasis claims rates and associated economic burden estimates are presented in Table 2. The annual trichomoniasis claims rate for all ages was 91 per 100,000 enrollees. Women aged 25 to 34 had the highest claims rate followed by those aged 15 to 24. The claims rate for women younger than 15 years was significantly lower (P < 0.01) than all other categories. The trichomoniasis incidence rate for women aged 20 to 29 years (175 per 100,000 enrollees) was significantly (P < 0.05) higher than those aged 30 to 39 years (142 per 100,000 enrollees). The finer age range analysis (5-year range) indicated that the highest incidence was among the 25- to 29-year age group followed by the 20- to 24-year age group (Fig. 1). Extrapolating to US women with employer-sponsored private insurance, the total annual number of cases receiving care was 67,400, giving an annual economic burden of $6.8 million. On the basis of the estimated initial physicians’ office visits for trichomoniasis in the CDC Surveillance report and assuming that the cases were distributed according to the age breakdown in the MEDSTAT claims data, the per episode costs we calculated suggest an average annual burden of $18.9 million for all women in the US population, regardless of insurance coverage; this is based on an average annual number of initial office visits of 185,000 for the years 2001 to 2005.3
The number of episodes and the resulting cost estimates were fairly stable (increasing by <2.2%) when we used a 15-day window instead of a 30-day window to define an episode, and the resulting cost estimates per episode were not significantly different.
In the 25,383 outpatient visits, there were 15,560 claims for procedures that could potentially have been used to diagnose trichomoniasis based on CPT codes. Many visits featured claims for more than 1 such procedure. The most common procedure was wet mount; wet mount claims appeared in 43.7% of total visits. The second most common diagnostic test was direct probe. The CPT code for a direct probe test specific for trichomoniasis (87,660) was used in 0.8% of visits, but a more generic direct probe CPT (87,797) was used in another 11% of visits. Claims for pap testing, which can be used to diagnose trichomoniasis, appeared in 3.7% of trichomoniasis-associated visits, and CPT codes for culture appeared in 2.5%. Trichomoniasis culture can also be coded as a wet mount test. The lack of specificity of CPT codes for these tests prevented more definitive analysis. Wet mount and direct probe were performed more often in women aged 20 to 29 years than (P < 0.01) in younger women (15–19 years) and women aged 40 and over, but not significantly different from women aged 30 to 39 years.
This study estimated direct medical cost and incidence of trichomoniasis, using the most recent data available on employer-sponsored private insurance claims. We estimated that overall average direct medical cost per episode was $101, which is substantially higher than published estimates for the same age category (after adjusting for inflation).26 Our estimated direct cost per episode is quite substantial and can be attributed to the cost of outpatient care. Prescription drug costs make up a small proportion of the total cost (<10%).
We estimated that the overall economic burden of trichomoniasis was $6.8 million among the employer-sponsored privately insured women, and $18.9 million among all women in the United States. Unlike a nationally representative survey that used biologic testing, which found a peak prevalence among women aged 30 to 39 years,5 we found that the incidence rate for women aged 20 to 29 years was significantly higher than those aged 30 to 39 years. The national survey is likely a more reliable measure than claims data because claims data only represent infections that received care and were coded correctly. Thus, the difference in these findings suggests that the distribution of privately insured individuals who receive care for trichomoniasis might differ from the prevalence of the infection in the general population.
We found that wet mount and direct probe were performed more often in women aged 20 to 29 years than (P < 0.01) in younger women (15–19 years), but not significantly different from older women (30–39 years). Given the lack of specificity of CPT codes for these tests and the suggestion in an earlier study that trichomoniasis care is incorrectly coded,3 it is possible that the higher rate in women aged 20 to 29 years found in our analyses is attributable to more frequent reproductive health care visits in which wet mounts and direct probe may be performed routinely compared to younger and older women. This could lead to a higher rate of diagnoses in this age group. It could also indicate that some care received by older women is coded differently, perhaps using a nonspecific ICD-9 code, such as that for vaginitis and vulvovaginitis (616.10).
Thus, while trichomoniasis causes similar sequelae to chlamydia and gonorrhea and is more common, it appears to have a strikingly different age distribution from other nonviral STDs. Although the age group with the highest rates found in this study was younger than the age group found in the population-based study5 (20–29 vs. 30–39 years), subsequent analyses found using 5-year range age groups in our study suggest that the age group with the highest trichomoniasis rates (25–29 years) is likely older than the age groups with the highest rates of primary and secondary syphilis (20–24 years), chlamydia, and gonorrhea (15–19 years) among women in the United States. Better understanding of the reasons for the older age distribution of trichomoniasis may enhance our understanding of the natural history of this infection, leading to more effective prevention and control efforts.
The asymptomatic nature of trichomoniasis,4,14,18 coupled with the fact that there are no recommendations for routine screening,14 likely is largely the reason for the relatively low claims rate found in this study compared to rates found in other studies.2–5 Nonspecific coding may also be one of the reasons for the relatively small number of initial office visits found in the National Disease and Therapeutic Index data.3 Also, several studies have reported that STD rates are higher in lower socioeconomic groups.32–35 This relationship was confirmed for trichomoniasis in a recent study that found that higher rates were associated with poverty and having a high school education or less.5 Thus, another reason for the relatively low rate found in this study compared to rates found in other studies is that the insured population belong to the higher socioeconomic group36 who have lower trichomoniasis rate.5
Our study has limitations associated with the use of medical claims data to estimate incidence and average cost per episode. First, it is difficult to differentiate between visits that represent follow-ups for a particular episode and those that represent repeat episodes, which eventually affects the cost and number of episodes estimated. To minimize this concern, we confirmed the robustness of our results by using 2 definitions for an episode based on the days of visits and found no significant difference in the results. The second limitation is partly a consequence 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). Thus, drug treatment costs were not found for some episodes. A third limitation is that the estimates are only representative of the employer-sponsored privately insured population and may not be representative of the entire US population. Despite the inherent limitations, our study provides, to our knowledge, the first direct estimate of the medical cost of trichomoniasis in the US employer-sponsored privately insured population. These estimates represent lower-bound estimates of the overall economic burden of trichomoniasis infection in these populations because we did not include other associated costs such as intangible costs and lost productivity costs in our per episode cost estimates. We also did not include the cost of sequelae such as preterm delivery, which could accrue even in cases that received no care coded under one of the ICD-9 codes we included in our analysis.
Trichomoniasis has been associated with other more costly sequelae13,15,16 and has been cited as one of the major STDs that increase the risk of HIV infection.21,22 Thus, the overall benefit of preventing trichomoniasis is substantially higher than the averted cost of medical care of trichomoniasis estimated in this study. The magnitude of the direct cost per episode, the high incidence among young women, and the possible association with other more serious diseases makes further research into prevention strategies worthwhile.
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