ALTHOUGH PEDICULOSIS PUBIS AND SCABIES are very common ectoparasitic infections, data on their incidence and economic burden are limited. The World Health Organization estimates that there are 300 million cases of scabies worldwide annually, but most cases are due to nonsexual transmission.1,2 A commonly cited estimate of the incidence of pediculosis in the United States is 3 million cases annually, but this figure is based on pediculocide sales and includes infestations attributable to head and body lice.3 Even if neither disease typically has serious morbidity, the overall economic burden could be substantial if either the cost per case or incidence is high. Pediculosis pubis can be treated with over-the-counter (OTC) medications,4 and patients may attempt self-treatment for scabies as well. However, professional care is also sought for both conditions.
The objectives of this study were to estimate the direct medical cost per case of pediculosis pubis and scabies treated on an outpatient basis and the rates at which outpatient care is sought using insurance claims data. Next, use the average direct medical cost and the estimated annual number of cases to determine a lower-bound estimate of the annual economic burden of scabies and pediculosis pubis infections for the employer-sponsored privately-insured population in the United States. To our knowledge, no published studies have investigated the incidence and economic burden of these infections. Estimates of both are useful and could facilitate future economic evaluation studies (such as cost-effectiveness and cost-benefit analyses) of programs or interventions designed to control and prevent sexually transmitted ectoparasitic infections.
We used outpatient and prescription drug claims data from the MarketScan database (MEDSTAT Group, Ann Arbor, MI) for 2001 through 2005. The MarketScan database contains data on persons who have employment-based health insurance and lists claims on over 5 million insured lives from more than 100 payers, including large employers, health plans, and government and public organizations (MarketScan Database, The MEDSTAT Group Inc). Over 60% of the entire insured population of the United States is enrolled in employer-sponsored private health plans. This allows projection of results of analyses of the MarketScan data to be representative of all privately-insured persons in the United States.5
We used International Classification of Diseases 9th revision codes to identify instances of outpatient treatment of scabies (code 133.0) and pubic lice (pediculosis pubis, code 132.2) in the database. We did not consider inpatient claims because patients would not be expected to be admitted solely for these ectoparasitic infections without any other contributing factors.
The Centers for Disease Control and Prevention (CDC) STD Treatment Guidelines recommend the use of 1% permethrin, pyrethrins with piperonyl butoxide, 0.5% malathion or ivermectin for treating pediculosis pubis, and 5% permethrin, 1% lindane or ivermectin for treating scabies.6 Pyrethrins with piperonyl butoxide and 1% permethrin are available OTC;4 the other treatments require a prescription in the United States. We used National Drug Codes to identify the use of these drugs in the MarketScan database (however, we found no drug claims for malathion). We then linked instances of claims for outpatient treatment for scabies and pediculosis pubis to prescription drug claims, under the assumption that prescription drugs received 7 days before through 30 days after the initial outpatient visit were associated with a given episode of an infection. Outpatient visits within 30 days of the initial outpatient visit were assumed to be part of the same episode of infection, as subsequent visits could reflect follow-up, persistent symptoms (rash and pruritus), or treatment failure. Outpatient visits 30 or more days after the initial outpatient visit were assumed to be attributable to a new episode of infection. Outpatient costs included diagnosis, test, procedure, and office visit costs paid by both enrollee and insurance plan. Drug costs included all prescription drug costs paid by both enrollee and insurance plan. The medical care component of the Consumer Price Index for All Urban Consumers was used to adjust all costs to 2005 US dollars. To calculate average costs per case and economic burden, 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. We used the annual enrollment information to estimate the incidence rate per 100,000 enrollees for outpatient care. We then used the person-level national weights to extrapolate the annual number of cases to reflect the total annual number of cases for the employer-sponsored privately-insured population in the United States. A more detailed description of the methods we applied is available from the lead author upon request.
Table 1 summarizes the insurance claims information and the estimated cost per case (weighted) of pubic lice and scabies when treated on an outpatient basis. For the 5-year period we examined, there were 858 and 32,737 patients treated for pubic lice and scabies, respectively, with 23% and 10% (of those with prescription drug coverage) having claims for prescription drugs, respectively. The average cost per case (including those who did not have drug claims) was $113 for pubic lice and $95 for scabies. 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 29% ($146) higher for pubic lice and 72% ($163) higher for scabies. Repeat episodes were uncommon. The average number of episodes per patient was 1.04 (range, 1–3) for pediculosis pubis and 1.09 (range, 1–8) for scabies. Incidence rates by sex and age group are presented in Table 2. The overall annual economic burden for pubic lice and scabies was approximately $0.4 million and $10.4 million, respectively for the employer-sponsored private insurance population in the United States. The number of episodes was fairly stable (increased by less than 2.6% and 1% for scabies and pubic lice, respectively) when we used a 15-day instead of a 30-day window to define an episode, and the resulting cost estimates per episode were not significantly different.
We estimated the incidence of outpatient care and cost per case of pediculosis pubis and scabies based on private insurance claims. We were not able to differentiate whether claims were based on infections acquired sexually or nonsexually. If our estimates were extrapolated to the US employer-sponsored private insurance population, we would estimate that there are 3400 and 110,300 episodes treated annually on an outpatient basis for pediculosis pubis and scabies, respectively. However, the true incidence of these ectoparasitic infections is likely substantially higher than the estimates we present (particularly for pediculosis pubis), because our analysis excludes cases that are self-treated (such as with the use of OTC permethrin for pubic lice). Information on self-treatment is not available in the database. Prescription drug claims may understate the extent to which drugs were prescribed for treatment, particularly in the case of scabies.
We estimated the direct medical costs of pediculosis pubis and scabies. We excluded direct nonmedical costs, such as the costs associated with environmental disinfection (laundering of clothing and treatment of nonwashable items).7 We also excluded indirect costs, such as lost productivity, which can be considerable. For example, for STDs such as chlamydia, the ratio of indirect to direct costs has been conservatively estimated at 0.5.8,9 Finally, we did not include intangible costs associated with pediculosis pubis and scabies (such as discomfort, embarrassment, and other psychosocial impacts), which can be substantial but are difficult to assess.
Thus, the total health and economic burden of these ectoparasitic infections is likely substantially higher than the estimates presented here. If the estimate of 3 million cases of louse infestation annually3 is correct, our direct medical cost per case would suggest a total burden of up to $339 million. However, because self-treatment likely involves the use of fewer resources than outpatient treatment, the average direct medical cost per case of these ectoparasitic infections overall (including self-treated and outpatient cases) is likely lower than the estimates we calculated. Another consideration is that we found that claims for care that could be defined as a repeat infection were rare; it is possible that reinfection is rare and also that patients receive instructions from clinicians that enable them to self-treat repeat infections.
There are limitations associated with using medical claims data to estimate the incidence and average cost per case of an infection. For example, treatment of pediculosis pubis and scabies may be underrecorded in the medical claims database, although we have no way of knowing the degree to which this may occur. However, providers will not receive payment without billing for it, and this incentive to providers is expected to limit the underrecording of treatment.10 We also note that underrecording of treatment would impact our incidence estimates but have little or no impact on the cost per case estimates. Additionally, the volumes of scabies code (133.0) and pubic lice code (132.2) were consistent over the years. We are also not aware of changes to the codes for scabies and pubic lice and/or coding system in the database during the years that we examined (2001–2005).
Medical claims data does not contain information on OTC treatments, which likely make up a substantial fraction of the treatments for scabies and pediculosis pubis infections. Secondly, it is not possible to differentiate between follow-up visits and visits for new episodes. This affects the cost and number of episodes estimated. However, we confirmed the robustness of our results by using 2 definitions for an episode based on the gap in days between of visits and found no significant difference in the estimates. Finally, the lack of well defined number of visits for each episode present the challenge of finding the associated treatment costs (drug claims). Thus we did not find drug treatment claims for some episodes.
Chart review might make it possible to determine which cases were a result of sexual transmission and contain information regarding whether patients were given guidance on purchase of OTC treatments. Although the MarketScan database is weighted to be representative of the employer-sponsored privately-insured population, cost estimates may not be representative of the US population as a whole.
Despite these and other limitations, our analysis provides data-based estimates of the incidence and cost per case of outpatient treatment of these ectoparasitic infections. These estimates help to quantify the health and economic burden of these infections and can prove useful in economic evaluations of interventions to prevent these infections.
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