The economic value of reductions in gonorrhea and syphilis incidence in the United States,

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1 Preventive Medicine 43 (2006) The economic value of reductions in gonorrhea and syphilis incidence in the United States, Harrell W. Chesson, Thomas L. Gift, Amy L.S. Pulver Division of STD Prevention, National Center for HIV, STD, and TB Prevention, Centers for Disease Control and Prevention, CDC Mailstop E-80, 1600 Clifton Road, Atlanta, GA 30333, USA Available online 8 August 2006 Abstract Background. Prevention efforts can reduce the considerable health and economic burdens imposed by sexually transmitted diseases (STDs). The objective of this study was to estimate the reduction in direct medical costs associated with reductions in gonorrhea and syphilis incidence in the United States from 1990 to Methods. Using published estimates of the per-case costs of STDs, we estimated the annual costs from 1990 to 2003 of four main outcomes: primary and secondary (P&S) syphilis, congenital syphilis, gonorrhea, and HIV costs attributable to the facilitative effects of gonorrhea and syphilis on HIV transmission and acquisition. Results. Reductions in syphilis and gonorrhea from 1990 to 2003 have saved an estimated $5.0 billion (in 2003 U.S. dollars): $1.1 billion in costs associated with P&S syphilis, congenital syphilis, and gonorrhea, and $3.9 billion in HIV costs attributable to syphilis and gonorrhea. In additional analyses, the estimated reductions in disease burden were substantially lower (1) when calculated incrementally (rather than cumulatively) and (2) when long-term costs of STDs were excluded. Conclusions. These estimated reductions in the burden of gonorrhea and syphilis show the economic benefits of reducing the incidence of these STDs and preventing their resurgence. Published by Elsevier Inc. Keywords: Gonorrhea; Syphilis; Syphilis, Congenital; HIV; Prevention and control; Cost of illness Introduction Sexually transmitted diseases (STDs) impose a considerable burden on the health of Americans. Almost 19 million new cases of STDs occur in the United States each year, and the annual direct medical costs of treating STDs (including HIV) and their sequelae are estimated at $11 to $17 billion ($2003 US) (Siegel, 1997; American Social Health Association, 1998; Chesson et al., 2004; Weinstock and Berman, 2004). Almost half of these STDs occur in young people aged years, at an estimated annual cost of $7.4 billion (Chesson et al., 2004; Weinstock and Berman, 2004). From 1990 to 2003, reported gonorrhea rates have declined from per 100,000 persons to per 100,000 persons, and primary and secondary (P&S) syphilis rates have declined from Corresponding author. Fax: address: hbc7@cdc.gov (H.W. Chesson) per 100,000 persons to 2.5 per 100,000 persons (Division of STD Prevention, 2004). The objective of this study was to estimate the reduction in direct medical costs associated with these reductions in gonorrhea and syphilis incidence from 1990 to Such estimates can be useful in examining the cost-effectiveness of STD prevention interventions and to inform decisions regarding the allocation of resources for STD prevention. Methods For each year from 1990 to 2003, we estimated the annual cost associated with syphilis and gonorrhea. We did not calculate changes in the annual cost of chlamydia, because the increase in reported chlamydia infections over the last decade is not likely attributable to actual increases in chlamydia in the US, but rather to increases in the number of states that require reporting of chlamydia cases, expansion of chlamydia screening activities, the use of increasingly sensitive diagnostic tests, and other factors (Division of STD Prevention, 2004). The annual cost estimates included the costs of four main outcomes: P&S syphilis, congenital syphilis, gonorrhea, and HIV costs attributable to the facilitative effects of gonorrhea and syphilis on HIV transmission and /$ - see front matter. Published by Elsevier Inc. doi: /j.ypmed

2 412 H.W. Chesson et al. / Preventive Medicine 43 (2006) Table 1 Estimates of the economic burden and the reduction of the economic burden of syphilis and gonorrhea in the United States, Item estimated Cost of syphilis and gonorrhea a Cost of HIV attributable to syphilis and gonorrhea Base case results Total costs, 1990 to 2003 $1.3 billion $2.5 billion $3.8 billion Total costs, 1990 to 2003, if syphilis and gonorrhea rates had $2.4 billion $6.4 billion $8.9 billion remained at 1990 levels Total reduction in costs from 1990 to 2003 c $1.1 billion d $3.9 billion $5.0 billion Additional analyses Total reduction in costs from 1990 to 2003, incremental cost scenario e $0.1 billion $0.4 billion $0.5 billion Total reduction in costs from 1990 to 2003, short-term cost scenario e $0.4 billion $0.0 billion $0.4 billion All costs are in 2003 US dollars. The column totals and the row totals are subject to rounding. a Includes costs of primary and secondary syphilis, congenital syphilis, and gonorrhea. b The estimated total reduction in costs is the total cost if syphilis and gonorrhea rates had remained at 1990 levels (row 2) minus the total cost based on actual reported syphilis and gonorrhea rates (row 1). c The total column includes the costs of P&S syphilis, congenital syphilis, and gonorrhea and the costs of HIV attributable to the syphilis and gonorrhea. d Of this $1.1 billion reduction, 63% is attributable to reductions in gonorrhea, 23% is attributable to reductions in P&S syphilis, and 14% is attributable to reductions in congenital syphilis. e The incremental cost scenario uses the previous year's incidence rate rather than the 1990 incidence rates as the comparison year to calculate reductions in burden. The short-term cost scenario uses 1990 incidence as the comparison year but includes only the costs associated with acute gonorrhea; primary, secondary, and early latent syphilis; and the first year of congenital syphilis. Total b acquisition. We calculated annual costs for each year by multiplying the reported number of new cases by published estimates of the cost per case. We also calculated the annual costs that would have been incurred if P&S syphilis, congenital syphilis, and gonorrhea rates had remained at 1990 levels for the entire period 1990 to All costs are reported in 2003 U.S. dollars, and previously published cost estimates were updated for inflation using the medical care component of the consumer price index from the Bureau of Labor Statistics ( We examined the lifetime cost of new STD cases that occurred each year (incidence costs) rather than the total cost each year of existing cases of STDs (prevalence costs). The cost per case of P&S syphilis ($506) included the cost of treatment of syphilis and the possible long-term sequelae costs associated with late benign syphilis, cardiovascular syphilis, or nuerosyphilis (Chesson et al., 2004). The cost per case of congenital syphilis ($5954) included the estimated first-year medical costs associated with congenital syphilis (de Lissovoy et al., 1995; Bateman et al., 1997), as long-term cost estimates for congenital syphilis were not available in the literature. The cost per case of gonorrhea differed for men ($60) and women ($303) and included the costs of diagnosis and treatment of acute infections and sequelae associated with delayed or inappropriate treatment (Chesson et al., 2004). The estimated lifetime cost per case of HIV ($254,567) included the costs of antiretroviral therapy, prophylaxis and treatment of opportunistic infections, and other medical care associated with HIV and AIDS (Holtgrave and Pinkerton, 1997). The annual number of reported cases of P&S syphilis, congenital syphilis, and gonorrhea (as well as population and vital statistics) was obtained from surveillance records maintained by the Centers for Disease Control and Prevention (CDC), available via the Internet ( (Division of STD Prevention, 2004). We also obtained population and vital statistics from various CDC and Bureau of the Census publications (U.S. Census Bureau, 2001, 2004; Hamilton et al., 2004). The estimated annual number of HIV cases attributable to syphilis and gonorrhea was calculated by assuming that the probability that a new case of STD will facilitate a new case of HIV is for syphilis and for gonorrhea (Chesson and Pinkerton, 2000). Additional analyses: incremental costs and short term costs In addition to the base case analysis described above, we calculated two alternative measures of the reduction in the burden of STDs since First, we calculated the incremental cost savings each year compared to the previous year's incidence rate, rather than using 1990 incidence rates as the comparison year for all years. That is, savings in 1991 were calculated as compared to 1990 incidence rates, savings in 1992 were calculated as compared to 1991 incidence rates, and so on. Second, we repeated the base case analysis focusing only on the reductions in the short term costs of STD, which excluded the costs of sequelae. The short-term cost per case of syphilis ($35) included the costs of treatment of primary, secondary, or early latent syphilis, adjusted for the probability of receiving treatment in one of these early stages, and excluded the potential costs of late syphilis, cardiovascular syphilis, and neurosyphilis (Chesson et al., 2004). The short-term cost per case of gonorrhea ($56 for men and $58 for women) included the cost of treating acute infection, adjusted for the probability of receiving treatment for acute infection, and excluded the potential costs of epididymitis in men and pelvic inflammatory disease (PID) in women (Chesson et al., 2004). The short-term cost for congenital syphilis ($5954) was the same as in the base case analysis, as the available cost estimates for congenital syphilis focus only on the first-year costs. For simplicity, and to keep our estimates conservative, we assumed $0 for the short-term costs of HIV attributable to syphilis and gonorrhea. Results Reductions in syphilis and gonorrhea from 1990 to 2003 have saved an estimated $5.0 billion in costs associated with P&S syphilis, congenital syphilis, gonorrhea, and HIV attributable to syphilis and gonorrhea (Table 1). The annual costs associated with P&S syphilis, congenital syphilis, and gonorrhea decreased from $163 million in 1990 to $69 million in 2003 (Fig. 1). Over the 14-year period from 1990 to 2003, the total cost of P&S syphilis, congenital syphilis, and gonorrhea was $1.3 billion (Table 1). If the rates for STDs had remained at 1990 levels and the cost per case for each STD had remained stable for all of these 14 years, the total costs of P&S syphilis, congenital syphilis, and gonorrhea would have been $2.4 billion, suggesting that the decreases in P&S syphilis, congenital syphilis, and gonorrhea since 1990 were associated with savings of $1.1 billion. The annual cost of HIV attributable to syphilis and gonorrhea decreased from $423 million in 1990 to $100 million in 2003 (Fig. 1). Over the 14-year period from 1990 to 2003, the total cost of HIV attributable to syphilis and gonorrhea was $2.5

3 H.W. Chesson et al. / Preventive Medicine 43 (2006) Fig. 1. Estimated economic burden of gonorrhea and syphilis, United States, billion (Table 1). If the rates for syphilis and gonorrhea had remained at 1990 levels, and if the average number of HIV cases attributable per case of syphilis and gonorrhea had remained constant, and if the cost per case for HIV had remained stable for all of these 14 years, the total costs of HIVattributable to syphilis and gonorrhea would have been $6.4 billion, suggesting that the decreases in syphilis and gonorrhea since 1990 were associated with savings of $3.9 billion in STD-attributable HIV costs. Additional analyses: incremental costs and short term costs When we calculated the incremental cost savings each year (using the previous year's incidence rate rather than the 1990 incidence rates as the comparison year), the estimated cumulative reduction in the STD burden was $0.5 billion when including HIV costs attributable to STDs and $0.1 billion when excluding HIV costs (Table 1). When we repeated the base case analysis focusing only on the reductions in the short term costs of STDs (and assuming no short-term costs of HIV attributable to STDs), the estimated cumulative reduction in the STD burden was $0.4 billion (Table 1). Discussion The decreases in syphilis and gonorrhea from 1990 to 2003 have saved an estimated $5.0 billion in direct medical costs associated with P&S syphilis, congenital syphilis, gonorrhea, and HIV attributable to syphilis. These estimated reductions in the burden of these STDs show the economic benefits of reductions in STDs and the value gained by preventing a resurgence of these diseases. The estimated $5.0 billion reduction in STD costs from 1990 to 2003 represents an average annual reduction of about $350 million. To put this estimate in perspective, the annual public investment in STD prevention (federal, state, and local) in 1995 (the most current year for which estimates of combined federal, state, and local STD prevention funding are available) was about $311 million (in 2003 U.S. dollars) (Institute of Medicine, 1997). It is likely that prevention efforts have contributed to the $5.0 billion decline in STD costs (Chesson et al., 2005; Chesson, in press). Had there been no prevention efforts, STD rates could have increased since If so, then it is possible that STD prevention efforts might account for a savings of even more than $5.0 billion, since we used 1990 STD rates as the comparison when we measured reductions in STD costs since However, STD prevention efforts might account for a savings of less than the $5.0 billion estimate since 1990, as some of the decrease in gonorrhea and syphilis may be attributable to factors other than STD prevention activities. For example, sexual behavioral changes in response to the AIDS epidemic (Becker and Joseph, 1988; Melnick et al., 1993; Feinleib and Michael, 1998), as well as disproportionate AIDS mortality among persons at high risk for acquiring STDs (Blower and van Griensven, 1993; Chesson et al., 2003; Boily et al., 2004), likely contributed to declines in STDs in the 1990s. Changes in STD rates might be attributable in part to changes in other factors that may influence STD rates, such as illegal drug use (Marx et al., 1991; Fullilove et al., 1993; Leigh and Stall, 1993), alcohol consumption (Chesson et al., 2000; Grossman et al., 2004), and underlying elements of STD epidemics such as poverty and health care coverage (Wasserheit and Aral, 1996; Kilmarx et al., 1997; Fox et al., 1998; Aral, 2002). It is also possible that changes in STD incidence in the 1990's may reflect oscillations attributable to the natural dynamics of STD infection (Grassly et al., 2005). Clearly, many factors besides STD prevention efforts can affect STD

4 414 H.W. Chesson et al. / Preventive Medicine 43 (2006) incidence rates, and more research is needed to estimate the reduction in STD costs that are attributable to STD prevention efforts. However, a recent cost-effectiveness study suggested that the effect of STD prevention efforts on gonorrhea incidence in the United States over time could be substantial, even if other factors besides prevention activities have a substantial influence on changes in gonorrhea incidence from year to year (Chesson, in press). Our $5.0 billion estimate of the reduction in the economic burden of STDs was calculated by comparing the annual burden of STD from 1990 to 2003 to the burden that would have been incurred if STD rates had remained at their 1990 levels. The estimated reduction in the burden of STDs was substantially lower in the additional analyses when we focused on incremental costs and short term costs. The reduction in the burden of STDs was $0.5 billion in the incremental cost scenario (when savings were calculated each year using the previous year's STD incidence rates for comparison, rather than using 1990 incidence rates) and $0.4 billion in the short term scenario (when only savings in short-term costs were included). In these alternative analyses, the estimated reductions ($0.5 billion and $0.4 billion) in the STD burden from 1990 to 2003 correspond to average annual reductions of about $32 million, which is substantially less than the $311 million in annual public investment in STD prevention activities (based on 1995 estimates). It is important to note, however, that these alternative analyses likely understate the true reduction in the burden of syphilis and gonorrhea. For example, the incremental cost scenario excludes the cumulative benefits of STD reductions over time by assuming that previous prevention activities had no impact. The short term cost scenario excludes the potential long-term costs of STDs. Furthermore, STD prevention activities can reduce the burden of other STDs not addressed in this study, such as chlamydia, human papillomavirus (HPV) infection, and genital herpes. Our estimates are based on two groups of inputs: the number of STD cases (syphilis, gonorrhea, congenital syphilis, and HIV attributable to syphilis and gonorrhea) and the estimated cost per case. Thus, our estimates are subject to the limitations associated with each of these two inputs. For example, if the cost estimates we applied per case of a given STD overstate or understate the actual cost per case, the estimated annual burden of that STD will be overstated or understated in a proportional manner. To keep our estimates conservative, we did not adjust for underreporting of gonorrhea and syphilis, which would have increased the estimated economic value of reductions substantially, assuming that the degree of under-reporting did not increase substantially from 1990 to Our estimates of the number of HIV cases attributable to the facilitative effects of syphilis and gonorrhea are subject to considerable uncertainty. Therefore, our estimate of the $5.0 billion reduction in the burden of STDs is better viewed as a rough estimate rather than a precise calculation. Alternatively, one could apply our $1.1 billion estimate (which excludes HIV costs attributable to syphilis and gonorrhea) as a conservative lower-bound estimate of the reduction in the burden of STDs. To keep our estimates conservative, we calculated only direct medical costs. The estimated reduction in the economic burden of STDs since 1990 would be even greater if we had included indirect and intangible costs (Blandford and Gift, in press). Although the costs we measured from 1990 to 2003 were updated for inflation to year 2003 dollars, the costs were not adjusted to their present value (i.e., a dollar saved 10 years in the past is worth more in present value than a dollar saved this year). If we had used a 3% annual discount rate to adjust past costs to present value, the estimated reduction in disease burden would have been about 15% greater than our unadjusted estimate. In summary, the costs associated with syphilis and gonorrhea have declined substantially since Despite its limitations, this analysis provides useful estimates of the reductions in the economic burden associated with syphilis and gonorrhea from 1990 to Acknowledgment The authors thank Kathleen Irwin for helpful comments. 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