In the united states, adolescents and young adults aged 15 to 24 years represent only one-quarter of the nation’s sexually active population, but acquire more than half of all incident cases of sexually transmitted infections (STIs) annually.1–6 Direct costs of curable and reportable STIs-Chlamydia, gonorrhea, and syphilis-are estimated at $329 million among American adolescents and young adults, and stem largely from the treatment of complications in women, such as pelvic inflammatory disease, ectopic pregnancy, and tubal infertility.1–4,7 Despite recognition of prevalent behavioral risks, the number of adolescents and young adults affected by STIs, and the cost and health impact of STIs, STI prevention efforts for adolescents and young adults face barriers as a funding priority.1,2,8 Quantifying the health and economic burden imposed by STIs among adolescents and young adults is vital for informing decisions on resource allocation and prevention program planning for leaders at the state and local government levels.1,2
We estimated the incidence and direct medical costs of 3 reportable, curable STIs-Chlamydia, gonorrhea, and syphilis-in individuals aged 15 to 24 years in the state of Illinois. Additionally, we examined provider type and testing location of reported STIs. Results of this analysis can aid in evaluating resource allocation at the county level, directing resources to the provider types with the highest disease burden, and the assessment of the sufficiency of current state resources for STI prevention among adolescents and young adults.1,2
MATERIALS AND METHODS
Study Population and Data Collection
The analysis was limited to disease surveillance case reports for persons aged 15 to 24 years, residing in Illinois. We excluded other prevalent, but nonreportable STIs (e.g., human papilloma virus, herpes simplex virus, Trichomonas vaginalis) due to inaccuracies in population morbidity estimates. In accordance with Illinois state law, health providers and laboratories are required to report contact and demographic information for cases of Chlamydia, gonorrhea, and syphilis confidentially to the local health department. A reported case of Chlamydia was defined as a laboratory-confirmed case of Chlamydia trachomatis. A reported case of gonorrhea was defined as a laboratory-confirmed case of Neisseria gonorrhoeae or by demonstration of Gram-negative intracellular diplococci in urethral or endocervical specimen. A case of primary or secondary syphilis was defined as dark-field-positive lesions or reactive serologic tests for syphilis and accompanying symptoms.
Data consisted of aggregated, deidentified counts of individually-reported cases from the Illinois Department of Public Health and included variables on sex, age, (15–19,20–24) race and ethnicity, and reporting source. Incidence rates and direct medical costs were estimated statewide and for the 10 counties with the greatest reported number of STIs by race, gender, age, and total population. The study protocol was approved by the Institutional Review Board of the University of Illinois at Chicago, School of Public Health.
Estimated Incidence of Disease
The number of reported cases in 15-to 24-year-olds was used to estimate the number of incident cases by taking into consideration the proportion of undiagnosed and unreported cases, based on information obtained in the literature. Rates were calculated by dividing the estimated number of incident cases of Chlamydia, gonorrhea, and syphilis by the estimated number of at-risk individuals aged 15 to 24 in Illinois, and are presented per 100,000 population. We estimated incidence rates separately for each infection, along with minimum and maximum estimates to reflect the uncertainty within our assumptions. The minimum incidence rate estimate represents the lowest number of estimated incident cases divided by the largest number of estimated at-risk population. The maximum incidence rate estimate represents the greatest number of estimated incident cases divided by the smallest number of estimated at-risk population.
Incidence Estimation: Numerators
The reported numbers of Chlamydia, gonorrhea, and primary and secondary syphilis (Reported cases and estimated incidence of primary and secondary syphilis were analyzed in aggregate due to small sample size) cases were assumed to underestimate incident disease; as these STIs are often asymptomatic and unreported, the actual incidence would be higher. Based on literature review, we estimated the proportion of each disease by gender that is undiagnosed and unreported, and specified a base estimate, with minimum and maximum ranges (Table 1). We used the same proportion of undiagnosed and unreported cases for gonorrhea and Chlamydia to create estimates of the actual disease burden. Estimated cases of syphilis were determined using separate estimates of the proportion of unreported and undiagnosed cases. The reported number of cases of Chlamydia, gonorrhea, and syphilis were divided by base, minimum, and maximum estimates for the proportion of undiagnosed and unreported cases, to estimate the base, minimum, and maximum number of incident cases each STI.
Incidence Estimation: Denominators
We used population estimates obtained from the US 2000 Population Census and the 2006 Illinois survey conducted by the Population Estimates Program in the US Census Bureau to determine the number of individuals aged 15 to 24 in Illinois and by county.14,15 To estimate the number of at-risk individuals, we used the National Survey on Family Growth, and the National Survey of Adolescents and Young Adults to estimate the proportion of adolescents and young adults who are sexually active,11,12 and derived a base, minimum, and maximum estimate of the percent sexually active (Table 1). The population estimates obtained from the US 2000 Population Census and the 2006 Illinois survey were divided by base, minimum, and maximum estimates of the percent sexually active to obtain estimates of the base, minimum, and maximum population at-risk.
Direct Medical Cost Estimates
Estimates of minimum, maximum, and base direct medical costs associated with disease were obtained from the literature. All costs were adjusted for inflation to year 2007 US dollars, using the medical care component of the Consumer Price Index for All Urban Consumers.16 We examined the direct medical lifetime costs of new STI cases occurring in Illinois adolescents and young adults in 2005 to 2006, using gender-specific cost-per-case estimates from published literature. These cost estimates include expenses needed to treat acute infections and the future costs of sequelae. To calculate the total direct medical cost for each STI, we multiplied minimum, maximum, and base cost-per-case estimates by the minimum, maximum, and base estimated incident cases, respectively. Costs were calculated by gender, race, and age.
A total of 98,083 cases of Chlamydia, gonorrhea, and syphilis were reported among 15- to 24-year-olds in Illinois in 2005 to 2006, accounting for >65% of reported cases statewide, with a total estimated direct cost of $71,727,328, ranging from $34,629,144 to $447,507,668. Cost estimates for 2005 and 2006 for each STI by gender are shown in Table 2. The reported cases and estimated incidence rate ranges by age and race are shown in Tables 3, 4, respectively. In 2006, over 80% of cases were reported from 4 provider types: private physicians/health maintenance organizations (31%), followed by nonemergency room hospital branches (24%), STD clinics (16%), and family planning clinics (11%).
In 2005, there were 5030 Chlamydia infections per 100,000 population and 5258 infections per 100,000 population in 2006 in individuals aged 15 to 24 in Illinois with estimated statewide direct medical cost of $27,576,686 in 2005 and $28,779,734 in this population (Table 2). Incidence was greater among women, with an estimated rate of 10,294 infections per 100,000 population in 2005, and 10,742 infections per 100,000 population in 2006. Rates were approximately the same for 15- to 19-year-old women and 20- to 24-year old women (not shown). In men, Chlamydia incidence was 2017 per 100,000 population in 2005 and 2121 per 100,000 population in 2006. In both 2005 and 2006, incidence of Chlamydia in men was approximately 3 times greater among 20- to 24-year-olds than 15- to 19-year-olds (not shown). The estimated direct medical cost of Chlamydia in women was $27,302,417 in 2005 and $28,491,131 in 2006, and $274,269 in 2005 and $288,603 in 2006 in men. By race, blacks had the highest rate of Chlamydia, increasing from 17,896 per 100,000 population in 2005, to 19,307 per 100,000 population in 2006 (Table 4). In 2005 and 2006, race was unreported for 16.7% and 14.5% of reported Chlamydia cases, respectively (results not shown).
Gonorrhea incidence among individuals aged 15 to 24 in Illinois was estimated at 1740 infections per 100,000 population in 2005, and 1705 infections per 100,000 population in 2006 with associated costs in this population of $7,698,135 in 2005, and $7,546,500 in 2006 (Table 2). Gonorrhea incidence was approximately 3 times greater in women than men. Rates were approximately the same for 15- to 19-year-old women and 20- to 24-year-old women (not shown). Gonorrhea incidence among men was greater in 20- to 24-year-olds (1228 per 100,000 population in 2005 and 1163 per 100,000 population in 2006) than 15- to 19-year olds (351 per 100,000 population in 2005 and 362 per 100,000 population in 2006). The estimated direct medical cost of gonorrhea in women was $7,534,692 in 2005 and $7,386,589 in 2006, and was estimated at $163,443 in 2005 and $159,911 in 2006 for men. By race, blacks had the highest rate of gonorrhea incidence, estimated at 8028 infections per 100,000 population in 2005, and 8223 infections per 100,000 population in 2006 (Table 4). In 2005 and 2006, race was unreported for 14.7% and 12.0% of reported gonorrhea cases, respectively (results not shown).
Primary and Secondary Syphilis
Overall incidence of P and S syphilis ranged from 6.59 to 16.6 per 100,000 population in 2005, and 7.29 to 18.4 per 100,000 population in 2006 (Table 2) in individuals aged 15 to 24 in Illinois. The cost of syphilis infection was estimated at $59,940 in 2005 and $66,333 in 2006 in individuals aged 15 to 24 in Illinois. Incidence of syphilis was 4.56 per 100,000 population in 2005 and 1.52 per 100,000 population in 2006 in women aged 15 to 19, and 7.89 per 100,000 population in 2005 and 5.26 per 100,000 population in 2006 in women aged 20 to 24. In men aged 15 to 19, incidence of syphilis was 3.65 per 100,000 population in 2005 and 4.38 per 100,000 population in 2006. Incidence rates were highest among men aged 20 to 24 (18.1 per 100,000 population in 2005 and 26.2 per 100,000 population in 2006). After higher estimated incidences in men, the total direct medical cost of primary and secondary syphilis infection in men were approximately double that of women in 2005, and 5 times greater in 2006. Syphilis rates were highest among blacks, ranging from 36.2 to 91.2 per 100,000 population in 2005, and 38.5 to 97.0 per 100,000 population in 2006 (Table 4). There were 2 cases of reported syphilis occurring in 2006 for which race was not reported.
Estimated Incidence Rates and Direct Medical Cost by County
Ten counties with the greatest reported counts of disease account for nearly 80% of reported cases of Chlamydia, gonorrhea, and primary and secondary syphilis among 15- to 24-year-olds in Illinois (Table 5). Counties with the highest incidence rates and cost estimates were located nearest to the Chicago (Cook, LAke, Will, DuPage) and St. Louis (St. Clair) metropolitan areas. The estimated incidence rate of STIs and associated costs was greatest in Cook County (which includes the city of Chicago), with 28,505 total estimated STI cases and direct medical cost of $15,955,349. Cases of STIs in Chicago account for approximately 73% of the total incidence and direct medical costs for Cook County. The distribution of disease by gender for each county was similar to the statewide distribution (results not shown).
There were striking differences in reporting sources by county (Table 6). Cook, St. Clair, Peoria, Lake, Kane, Will, Champaign, and DuPage counties had no cases of disease reported from hospital emergency rooms, whereas Winnebago and Sangamon counties had a significant proportion of cases, 21% and 8%, respectively, reported from hospital emergency rooms. Family Planning was the reporting source for <8% of cases in Cook, Winnebago, Will and DuPage counties, but accounted for more than 15% of cases reported in Peoria, Sangamon, and Champaign. The majority of cases in all counties were reported from STD clinics, nonemergency room hospital branches, private physician/health maintenance organizations, and unknown sources.
We estimate there are nearly 50,000 incident of Chlamydia, gonorrhea, and primary and secondary syphilis occurring annually among Illinois youth aged 15 to 24 years, with associated annual costs of treatment of approximately $35 million. The estimated economic burden of STIs is substantial due to the high estimated incidence of infection. The annual expenditure on health in the state of Illinois is approximately $67 billion.17 The cost to treat Chlamydia, gonorrhea, and primary and secondary syphilis among Illinois adolescents and young adults represents only 0.05% of the total expenditure on health. In Illinois, 15- to 24-year-olds account for approximately 13% of the state population.14 If this age group accounts for 13% of the annual expenditure on health, the estimated cost of incident STIs could reach upwards of 40% of the total annual statewide health expenditure for 15- to 24-year-olds. If 15- to 24-year-olds account for a smaller proportion of annual health expenditure then the direct medical cost of STIs may comprise an even greater proportion of total health expenditure in this age group. By comparison, IL spends approximately $6.5 million from the Centers for Disease Control STD prevention funds a year.17 Thus a reduction in the disease burden of STIs in youth and adolescents may have a significant impact on the total health expenditure in 15 to 24 year-olds.
As stated in the results, greater than 65% of all reported cases statewide (regardless of age) were attributed to individuals aged 15 to 24. Additionally, 10 counties in Illinois accounted for greater than 80% of the reported cases in the entire state. Previous STI resource allocation recommendations have focused on prevention programs targeted at high-risk groups. An approach that combines targeted programs towards adolescents and young adults, while focusing on the highest disease rates geographically, may maximize long-term health benefits and cost savings.
Consistent with other studies, the estimated cost attributed to these STIs is higher in women than in men. Women are more susceptible to complications from STIs, with higher costs stemming from more complex and intensive health care delivered in emergency departments, surgery departments, and inpatient settings.1,4 Additionally, women had a higher estimated incidence of Chlamydia and gonorrhea than men, stemming from greater numbers of reported cases. Women are more likely than men to be screened for STIs, but also many STIs are more easily transmitted from men-to-women than from women-to-men, which might account for the higher rates of disease among women compared with men.1,3,6,18
The estimated incidence of all STIs was higher among individuals aged 20 to 24 and blacks. Incidence of disease was most likely higher among the older age groups due to an increase in the proportion sexually active individuals in the population. An increase in the proportion of sexually active individuals increases the probability of contact with an individual infected with an STI. The reasons for higher rates of STIs among blacks are unclear, but our estimates are in keeping with national estimates of disease by race. Associated factors may include varying risks of STIs among sexual networks, differing access to healthcare, socioeconomic status, or differences in sexual behavior.1,3,5
These estimated incidence rates and costs of STIs among Illinois adolescents and young adults should not be viewed as exact, but rather as ranges due to the uncertainty within our assumptions. Surveillance data underrepresent true STI incidence by 50% or more as many STI cases are not reported.1 A large proportion of STIs in men and women are asymptomatic and remain undiagnosed.1,3,6–7,9,18,19 STI screening reduces the number of infections that go undetected; however, variability in diagnostic accuracy of different screening assays can lead to differences in detection of asymptomatic infections,5,9,10 and differences in health care may affect the numbers of people who are screened for infection. Sources of healthcare, access, and payment sources differ by age, gender, and race, which affect the number of individuals screened, reported infections, estimates of asymptomatic infections, and subsequently, estimated incidence and costs.8,10
STIs are treated at a variety of health care facilities, and may be reported with differing regularity.6,10,19 Additionally, health care facilities may treat STIs presumptively, without confirmatory laboratory diagnosis, leading to underestimate of incident infections.10,19 In our analysis, the proportion of STIs reported by provider type varied significantly by county. Because it is unlikely that such variability exists in the actual incidence of infection for provider type (e.g., no reported STIs from Cook County emergency room compared to 21% for Winnebago County), the differing distribution of provider type between counties likely indicates inadequacies in the reporting structure for STIs in Illinois. Additionally, low counts of STIs from various reporting sources may be influenced by private sector nonreporting.
In this analysis, our estimates included broad ranges of assumptions for underreporting and undiagnosed infection; currently, there is insufficient information to narrow this range. Information concerning reasons for treatment (e.g., screening, contact, symptoms), diagnostic test, and treatment may help to more precisely estimate the number of individuals with incident STIs. We did not know the proportion of cases that were detected by screening or diagnosis due to clinical presentation. Cost estimates represent treatment of complicated and uncomplicated infections, and do not differentiate between symptomatic and asymptomatic infection. Because this information is not reported, it is unable to be estimated or measured.
We calculated incidence rates of Chlamydia, gonorrhea, and syphilis by race. Reporting by race assumes that individuals are not of multiple races, thereby potentially over or underestimating the number of infections for a particular race. Discrepancies exist between the categorizations of race when reporting STIs in Illinois and categorizations of race taken by the US census. Although categories of race in the US census were condensed to most closely reflect the categories of race reported to the Illinois Department of Public Health, such adjustment may cause less accurate estimations of incidence by race. Furthermore, race is frequently incorrectly categorized in reporting cases to the health department, and for a significant proportion of reported cases of gonorrhea and Chlamydia race was unknown or missing. For these reasons, and because race is not a reliable indicator of socioeconomic status or geographic residence, we felt a cost estimate of STIs by race would not be useful in resource allocation. Underreporting and misclassification make it difficult to accurately estimate the disease burden in Illinois by race and ethnicity. Evaluation of STI burden by geographic region, gender, age, and provider type may provide more useful information for resource allocation and targeted interventions.
Estimated direct medical costs for each STI were taken from the literature. Our cost estimates for syphilis assumes the same cost for men and women. Because of differences in the course of infection between men and women, a uniform cost may lead to inaccuracies in our estimation. As prospective measures would have been needed, we could not measure STI-attributable HIV. This analysis was limited to individuals aged 15 to 24 in the state of Illinois; the rates and cost ranges presented represent only a fraction of the disease and economic burden of STIs in Illinois. This analysis was restricted to direct medical costs to treat STIs among Illinois young adults and adolescents. Indirect and intangible costs, such as productive losses due to STI-related illness or pain and suffering, should also be addressed when estimating the economic burden of STIs. The recognition of indirect and intangible costs may help to increase the acceptability of STI prevention programs.20
This article provides a practical range of direct medical costs of 3 reportable and curable STIs among Illinois adolescents and young adults age 15 to 24. More valid incidence and cost estimates may be generated with expanded and improved reporting regarding STI history and reason for testing. The utility of estimates may be increased with more precise geographic information. Ten counties accounted for >80% of the statewide estimated morbidity and costs for adolescents and young adults. Because of the high prevalence and incidence of STIs in adolescents and young adults, directing resources and programs towards adolescents will maximize long-term health benefits and cost savings. The effectiveness of Illinois STI prevention efforts may be maximized at reducing the overall burden of disease and associated costs if focused on the highest disease rates geographically, rather than by specific STI or at-risk population.
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