Sexually Transmitted Diseases  >  Surveillance & Statistics  >  Indian Health Surveillance Report, STDs 2004

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Data Sources and Limitations

Nationally notifiable disease data, including data for STDs, are submitted to CDC from state health departments (and other local reporting jurisdictions) and are stored at the National Center for Public Health Informatics (NCPHI), formerly known as the Epidemiology Program Office (EPO). In 2004, there were over 65 nationally notifiable infectious diseases and conditions.⁴ Surveillance data for notifiable STDs are electronically sent from NCPHI to the Division of STD Prevention (DSTD), where they are combined with hard copy data (also sent from state and local jurisdictions) to create the National STD Surveillance System (STDSS).

Numerators: Incident STD Cases Reported to CDC

All of the STD data in this report are based on cases of nationally notifiable STDs reported to CDC from the STD control programs and health departments in the 50 states, the District of Columbia (DC), and selected large U.S. cities. In aggregate, the STD cases reported from all of these jurisdictions are used when calculating U.S. rates. STD data from U.S. dependencies and territories (e.g. Guam, Puerto Rico, Virgin Islands) are not included in the U.S. rates or for any other rates used in this report.

AI/AN rates (as shown in the National STD Profile section) are based on STD cases which occurred among persons identified as AI/AN residing in all jurisdictions. In contrast, IHS rates (as shown in the IHS Area STD Profiles) are based on a subset of all AI/AN STD cases. The IHS rates include only STD cases which occurred among AI/AN residing in counties where IHS has responsibilities (see IHS Denominators for further details); these STD cases may or may not have been diagnosed in IHS, tribal, or urban Indian healthcare facilities. These definitions of AI/AN rates and IHS rates are used consistently throughout this publication.

STD Data Sources and Reporting Formats

In the past, STD data were submitted by state STD prevention programs to CDC on a variety of hard copy summary reporting forms (monthly, quarterly, and annually). As of December 31, 2003, all 50 states and DC had converted from summary hard copy reporting to electronic submission of line-listed (i.e. case-specific) STD data via the National Electronic Telecommunications System for Surveillance (NETSS). Data reported through NETSS comprise the notifiable disease information that is published in the Morbidity and Mortality Weekly Report (MMWR).

The data presented in the National STD Profile are from STDSS and are based on a combination of aggregated final NETSS electronic data and summary hard copy reporting forms. Monthly hard copy reporting forms include summary data for syphilis by county and state. Quarterly hard copy reporting forms include summary data for gonorrhea, chlamydia, syphilis, and other STDs by sex and source of report (STD clinic or non-STD clinic) for the 50 states, 64 selected cities, and outlying areas of the U.S. Annual hardcopy reporting forms include summary data for chlamydia, gonorrhea, and primary and secondary syphilis (P&S) by age, race, and sex for the 50 states, DC, and 6 large city project areas.

The IHS-specific data presented in the IHS Area STD Profiles come only from NETSS and do not include data from hard copy reporting forms. IHS Area data presented in this report require STD datasets which contain both race and county variables in order to determine which cases are AI/AN and to assign cases to the appropriate IHS Area (based on the patient’s county of residence). These variables are generally available only with NETSS line-listed data. Data contained in the IHS Area STD Profiles are restricted to years when STD cases submitted to NETSS were relatively complete for most states and reporting jurisdictions (i.e. 1998-present).

2004 case reports and corrections sent to CDC through April 29, 2005 have been included in this report. Data and corrections received after this date will appear in subsequent issues and updates.

Adjustments to CDC STD Data

In order to improve the quality of certain national and IHS Area analyses, several adjustments were made to the data prior to calculating rates. These procedures removed or redistributed cases and populations when one or more of the following conditions were present:

• If a state had >50% of its cases with unknown race/ethnicity, both the cases and populations were removed from the case and population databases prior to performing analyses involving race/ethnicity.
• If a state had ≤50% of its cases with unknown race/ethnicity, the cases with unknown race/ethnicity were redistributed to known race/ethnicity categories, based on the percentage of cases in each known category. This adjustment was made after cases had been summed over the geographic unit of the analysis (e.g. national, state, county, IHS Area).
• If a state did not report any cases to NETSS, the populations of those states were removed from the population database. This adjustment was made only for IHS and IHS Area analyses.

For U.S. cases and rates shown in this report, adjustments were made depending on the type of analysis in order to maintain consistency between data presented in this report and data presented in the CDC STD Surveillance Summaries.³ Unadjusted U.S. case counts and rates are presented for STD totals and for analyses by sex; adjusted U.S. case counts and rates are presented for analyses by sex and age.

Population Denominators and Rate Calculations

Crude incidence rates (new cases/population) were calculated on an annual basis per 100,000 population. In this report, the 2004 rates for the U.S., IHS, and individual IHS Areas were calculated by dividing the number of cases reported from each area in 2004 by corresponding 2003 population estimates. For subsequent reports, the 2004 rates will be updated using 2004 populations. For all other years, rates were calculated by dividing annual cases by the appropriate population estimate (e.g. 2001 cases divided by 2001 population). Specifics on population denominators used in this report are detailed below.

U.S. Denominators

For years 2000-2004, rates were calculated using the Census 2000 bridged-race file developed by the Census Bureau and the National Center for Health Statistics (NCHS). Census 2000 was the first census to allow for racial identification as either a single race or in combination with other races; consequently, the Census 2000 data on race are not directly comparable with data from the 1990 census or earlier censuses. To address this inconsistency, NCHS and the Census Bureau developed the Census 2000 bridged-race file,⁵ which bridges the 31 race categories specified in the 1997 Office of Management and Budget (OMB) standards (used in Census 2000) with the 4 race categories specified under 1977 OMB standards (used in the 1980 and 1990 censuses).⁶

For years 1990-1999, population counts were also updated to incorporate the bridged-race estimates based on the Census 2000 counts.⁵ These files were prepared by the Census Bureau with support from the National Cancer Institute.

U.S. rates for 1984-1989 were calculated using Census Bureau population estimates for corresponding years.⁷

AI/AN Denominators (National STD Profile)

National AI/AN rates, like U.S. rates, were calculated using national-level census population estimates. For 1984-1989, rates were calculated using AI/AN-specific Census Bureau population estimates.⁵ For 1990-2004, rates were calculated based on estimates of identified AI/AN in the Census 2000 bridged-race file.⁶

IHS Denominators (IHS Area STD Profiles)

Population denominators used to calculate IHS rates are based on estimates of AI/AN identified to be eligible for IHS services (i.e. the IHS eligible population). IHS eligible population estimates are unique to this publication and are based on official county estimates from the Census 2000 bridged-race file. The Census Bureau enumerates those individuals who self-identify as being AI/AN. The IHS eligible population is estimated by counting those AI/AN (as self-identified during the Census) who reside in specified counties in which IHS has responsibilities (“on or near” reservations)—within IHS, these counties are commonly referred to as contract health service delivery areas (CHSDAs) or service counties. In 2004, there were 624 service counties in 35 states; the current listing of service counties can be obtained by contacting IHS DPS at IHSStatsHelp@ihs.gov. Based on current service counties, the estimated overall 2004 IHS eligible population is 1.74 million persons, comprising 60 percent of all AI/AN residing in the U.S. These people may or may not use IHS services.

IHS eligible population estimates are similar, but not identical, to IHS service population estimates, which are official IHS population counts referenced in IHS publications^1,2 and used by IHS when calculating AI/AN natality/ mortality rates and other health statistics. In contrast to IHS eligible population estimates, IHS service population estimates are further adjusted using an intercensal smoothing process based on the most current 10 years of AI/AN natality and mortality data. This adjustment results in small differences between the IHS eligible and IHS service population estimates.^{Appendix A} Overall, in 2004, IHS eligible population estimates were 1.5% lower than IHS service population estimates (1,742,040 vs. 1,769,451, respectively). For individual IHS Areas, IHS eligible population estimates (when compared to IHS service population estimates) ranged between 4.9% lower in the Oklahoma City Area and 4.9% higher in the Phoenix Area.

Healthy People 2010 Objectives

In January 2000, CDC released Healthy People 2010 (HP 2010), a set of health objectives for the U.S. to achieve over the first decade of the new century.⁸ The year 2010 targets for the diseases addressed in this report are: gonorrhea—19 cases per 100,000 population, and primary and secondary syphilis—0.2 case per 100,000 population.

Data Limitations and Clarifications

AI/AN and Hispanic Ethnicity

IHS-specific rates shown in the IHS Area Profiles section of this report are based on case reports and population estimates for all individuals identified as AI/AN, including AI/AN Hispanics and AI/AN non-Hispanics. This methodology is consistent with current practices at IHS DPS.

In contrast, AI/AN STD rates shown in the National STD Profile and as published in the annual CDC STD Surveillance Summaries include case reports and population estimates only for AI/AN non-Hispanics; STD cases which occurred among AI/AN Hispanics are included in the Hispanic rates.

Differences in how AI/AN Hispanics are categorized in the National Profile vs. IHS Area Profiles result from differences in how primary data were collected in the STDSS and NETSS datasets.

Misreporting of AI/AN Race

Previous studies have documented misreporting of AI/AN race on death certificates and in state STD surveillance databases,^9,10 resulting in underestimates when characterizing the burden of disease among AI/AN people. Misreporting of AI/AN race occurs particularly in areas distant from traditional AI/AN reservations.⁹ AI/AN and IHS rates presented in this report have not been adjusted for racial misreporting.

IHS Areas Containing Partial Service Counties

Five of the IHS Areas (Albuquerque, California, Navajo, Phoenix, and Tucson) contain service counties which are shared between IHS Areas or are partially contained within an IHS Area. For these 17 partial service counties,^{Appendix B} IHS DPS has developed “percentage splits” (based on the 1990 census), which determine what proportion of the county’s AI/AN population lies within the jurisdiction of a given IHS Area. These percentage splits, which are based on geographic boundaries, tribal population counts, and health care utilization data, are updated periodically.

For chlamydia and gonorrhea rates presented in this report, case counts and IHS populations for partial service counties were determined using percentage splits. This is the same methodology that IHS DPS currently uses when calculating natality and mortality rates involving partial service counties.

Because primary and secondary syphilis (P&S) rates are significantly lower than chlamydia and gonorrhea rates, attributing cases which occurred in partial service counties based on percentage splits could lead to substantial differences in rates as described in this report compared to actual disease rates. For the P&S cases which occurred in partial service counties during 1998-2004, we adjusted rates by reviewing case data with state STD database managers to determine which IHS Area the case should be assigned to, based on the patient’s community of residence. Adjusted P&S case counts and rates are shown for the 4 affected IHS Areas (Albuquerque, Navajo, Phoenix, and Tucson); no P&S cases were reported among AI/AN residing in partial service counties within the California Area.

Urban Indians and Non-Federally Recognized Tribes

STD data specific to urban Indians and non-federally recognized tribes are not included in this report. Methodologies to describe STD rates in these populations must still be developed. Such data may be included in future issues and updates.

Reporting Practices

Although most areas generally adhere to the case definitions for STDs found in Case Definitions for Infectious Conditions under Public Health Surveillance,¹¹ there may be differences in the policies and systems for collecting surveillance data. Thus, comparisons of case numbers and rates among areas should be interpreted
with caution. However, since case definitions and surveillance activities within a given area remain relatively stable, trends should be minimally affected by these differences. In many areas, the reporting from publicly supported institutions (e.g. STD clinics and IHS, tribal, or urban Indian health organizations) has been more complete than from other sources (e.g. private practitioners). Thus, trends may not be representative of all segments of the population.

Reporting of Chlamydia Cases

Trends in chlamydia case reporting from many states and areas are more reflective of changes in testing, diagnosis, and reporting of cases, rather than actual trends in disease incidence. Because of this limitation, the CDC primarily monitors chlamydia trends not by rates (number of positive cases/population), but by positivity or estimated prevalence (number of positive cases/number tested).¹² In areas where chlamydia positivity data are limited or not available, it is important to publish data on chlamydia rates (as provided in this report) in order to emphasize the large numbers of chlamydia cases being detected. Currently, chlamydia positivity data are not readily available for any of the IHS Areas.

Interpretation of Case Rates when Case Counts are Small

STD case rates for many analyses presented in this report are based on small case counts (e.g. ≤20 cases); such rates and trends should be interpreted with caution. Small case counts occur in analyses by sex and age, P&S analyses, and analyses involving IHS Areas with small populations (e.g. Tucson and Billings). Case counts corresponding to all rates shown in this report are provided in the Tables section.

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