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Sexually Transmitted Diseases
Sexually Transmitted Diseases  >  Surveillance & Statistics  >  2006 Reports  >  Table of Contents  >  Appendix - Interpreting STD Surveillance Data
STD Surveillance 2006

Interpreting STD Surveillance Data

Sexually Transmitted Disease Surveillance, 2006 presents surveillance information derived from the official statistics for the reported occurrence of nationally notifiable sexually transmitted diseases in the United States, test positivity and prevalence data from numerous prevalence monitoring initiatives, sentinel surveillance of gonococcal antimicrobial resistance, and national health care services surveys.

Nationally Notifiable STD Surveillance

Nationally notifiable STD surveillance data are collected and compiled from reports sent by the STD control programs and health departments in the 50 states, the District of Columbia, selected cities, U.S. dependencies and possessions, and independent nations in free association with the United States to the Division of STD Prevention (DSTDP), National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention (NCHHSTP), Centers for Disease Control and Prevention (CDC). Included among the dependencies, possessions, and independent nations are Guam, Puerto Rico, and the Virgin Islands. These entities are identified as "outlying areas" of the United States in selected figures and tables.

Reporting Formats

STD morbidity data presented in this report are compiled from a combination of data reported on standardized hardcopy report forms and electronic data received via the National Electronic Telecommunications System for Surveillance (NETSS).

Summary Report Forms (hardcopy format)

The following hardcopy forms were used to report national STD morbidity data:

  1. FORM CDC 73.998: Monthly Surveillance Report of Early Syphilis.This monthly hardcopy reporting form was used from 1984 to 2002 to report summary data for P&S syphilis and early latent syphilis by county and state.
  2. FORM CDC 73.688: Sexually Transmitted Disease Morbidity Report.This quarterly hardcopy reporting form was used from 1963 to 2002 to report summary data for all stages of syphilis, congenital syphilis, gonorrhea, chancroid, chlamydia, and other STDs by sex and source of report (private vs. public) for the 50 states, Washington, D.C., and 64 selected cities (including San Juan, Puerto Rico) and outlying areas of the United States. Note: genital chlamydial infection became a nationally notifiable condition in 1996, and the form was modified to support reporting of chlamydia that year. Congenital syphilis was dropped from this aggregate form in 1995 and replaced by the case-specific CDC 73.126 form listed below.
  3. FORM CDC 73.2638: Report of Civilian Cases of Primary & Secondary Syphilis, Gonorrhea, and Chlamydia by Reporting Source, Sex, Race/Ethnicity, and Age Group. This annual hardcopy form was used from 1981 to 2002 to report summary data for P&S syphilis, gonorrhea, and chlamydia by age, race, sex and source (public vs. private) for all states and seven large cities (Baltimore, Chicago, New York City, Los Angeles, Philadelphia, San Francisco, and Washington, D.C.), and outlying areas of the United States. Note: genital chlamydial infection became a nationally notifiable condition in 1996 and the form was modified to support reporting of chlamydia that year.
  4. FORM CDC 73.126: Congenital Syphilis (CS) Case Investigation and Report. This case-specific hardcopy form was first used in 1983 and continues to be used to report detailed case-specific data for congenital syphilis in some reporting areas.

National Electronic Telecommunications System for Surveillance (NETSS, electronic format)

Notifiable STD data reported electronically through NETSS comprise the nationally notifiable disease information that is published in the Morbidity and Mortality Weekly Report (MMWR).

As of December 31, 2003, all 50 states and Washington, D.C. had converted from summary hardcopy reporting to electronic submission of line-listed (i.e., case-specific) STD data via NETSS (41 reporting areas are submitting congenital syphilis surveillance data via NETSS). Puerto Rico converted to electronic reporting in 2006. Guam and the Virgin Islands continue to report using summary hardcopy forms.

Jurisdictions differ in their ability to resolve differences in total cases derived from summary hardcopy monthly, quarterly, and annual reports (as well as electronically submitted line-listed data). Thus, depending on the database used, there may be discrepancies in the total number of cases among the figures and tables for earlier years. In most instances, these discrepancies are less than 5% of total reported cases and have minimal impact on national case totals and rates. However, for a specific jurisdiction, the discrepancies may be larger.

Surveillance data and updates sent to CDC on hardcopy forms and for NETSS electronic data through June 22, 2007 have been included in this report. Data received after this date will appear in subsequent annual Surveillance Reports. The data presented in the figures and tables in this document supersede those in all earlier publications.

Population Denominators and Rate Calculations

2000 - 2006 Rates and Population

Crude incidence rates (new cases/population) were calculated on an annual basis per 100,000 population. In this report, the 2006 rates for the United States, all states, counties, metropolitan statistical areas (MSAs), and outlying areas were calculated by dividing the number of cases reported from each area in 2006 by the estimated area-specific 2005 population (the most current detailed population file available at time of publication).

The National Center for Health Statistics released bridged race population counts for 2000 - 2005 resident population based on the Census 2000 counts. These estimates resulted from bridging the 31 race categories used in Census 2000, as specified in the 1997 Office of Management and Budget (OMB) standards, to the five race/ethnicity groups specified under the 1977 OMB standards.

From 2001 to 2002, population estimates for Guam were obtained from the Guam Bureau of Statistics and Plans; estimates for Puerto Rico were obtained from the Bureau of Census; and estimates for the Virgin Islands were obtained from the University of the Virgin Islands. After 2002, population estimates for all outlying areas were obtained from the Bureau of Census web site . The 2005 - 2006 rates for outlying areas were calculated using the 2005 population estimates.

Due to use of the updated population data, rates for the period 2000 - 2005 may be different from prior Surveillance Reports.

1990 - 1999 Rates and Population

The population counts for 1990 - 1999 incorporated the bridged single-race estimates of the April 1, 2000 resident population. These files were prepared by the U.S. Census Bureau with support from the National Cancer Institute.

1981 - 1989 Rates and Population

For the United States, rates were calculated using Bureau of the Census population estimates for 1981 through 1989 (Bureau of the Census; United States Population Estimates by Age, Sex and Race:1980 - 1989 [Series P-25, No. 1045]; Washington: U.S. Government Printing Office, 1990; and United States Population Estimates by Age, Sex and Race: 1989 [Series P-25, No. 1057]; Washington: U.S. Government Printing Office, 1990.

1941 - 1980 Rates and Population

Rates for 1941-1980 are based on population estimates from the Bureau of Census and currently maintained by the Division of STD Prevention.

1941 - 2006 Congenital Syphilis Rates and Live Births

Congenital syphilis (CS) data in Table 1 of Sexually Transmitted Disease Surveillance 2006 present the number of congenital syphilis cases per 100,000 live births for all years during the period 1941 through 2006. Previous publications presented congenital syphilis rates per 100,000 population for 1941-1994 and for cases diagnosed at < 1 year of age per 100,000 live births. To allow for trends in CS rates to be compared over time, beginning in 2006 live births will be used as the denominator for CS and case counts will no longer be limited to those diagnosed within the first year of life. CS morbidity (cases) are assigned to their year of birth. Rates of congenital syphilis for 1963-1988 were calculated using published live birth data (NCHS; Vital Statistics Report, United States, 1988 [Vol.1-Natality]). Congenital syphilis rates for 1989-2003 were calculated using live births from the National Center for Health Statistics (NCHS) (Vital Statistics: Natality Tapes 1989-2002 or Vital Statistics Reports, United States 1999, Vol. 48 No.10-Natality). Race-specific rates for 2004-2006 were calculated using live birth data for 2004.

Reporting Practices

Although most areas generally adhere to the national notifiable STD case definitions collaboratively developed by the Council of State and Territorial Epidemiologists (CSTE) and CDC, there may be differences in the policies and systems for collecting surveillance data. Thus, comparisons of case numbers and rates between jurisdictions should be interpreted with caution. However, since case definitions and surveillance activities within a given area remain relatively stable over time, trends should be minimally affected by these differences. In many areas, the reporting from publicly supported institutions (e.g., STD clinics) 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 Metropolitan Statistical Area-specific Surveillance Data

Sexually Transmitted Disease Surveillance, 2006 continues the presentation of STD incidence data and rates for the fifty Metropolitan Statistical Areas (MSAs) with the largest populations based on 2000 U.S. Census data. Sexually Transmitted Disease Surveillance reports prior to 2005 presented data by selected cities which estimated city-specific morbidity and were derived from county data. Since county data were used to estimate city-specific morbidity and current STD project areas' reporting practices do not support direct identification of city-specific morbidity reports, MSAs (described below) were chosen as a geographic unit smaller than a state or territory for presentation of STD morbidity data.

Metropolitan Statistical Areas are defined by the Office of Management and Budget to provide nationally consistent definitions for collecting, tabulating, and publishing federal statistics for a set of geographic areas.1   An MSA is associated with at least one urbanized area that has a population of at least 50,000. The MSA comprises the central county or counties containing the core, plus adjacent outlying counties having a high degree of social and economic integration with the central county as measured through commuting. The title of an MSA includes the name of its principal city with the largest Census 2000 population. If there are multiple principal cities, the names of the second largest and third largest principal cities appear in the title in order of descending population size.

The MSA concept has been used as a statistical representation of the social and economic linkages between urban cores and outlying, integrated areas. However, MSAs do not equate to an urban-rural classification; all counties included in MSAs and many other counties contain both urban and rural territory and populations. Programs that treat all parts of an MSA as if they were as urban as the densely settled core ignore the rural conditions that may exist in some parts of the area. In short, MSAs are not designed as a general purpose geographic framework for nonstatistical activities or for use in program funding formulas.

For more information on MSA definitions used in this report, please visit this web site: 

Management of Unknown, Missing or Invalid Age Group, Race/Ethnicity, and Sex Data

The percentage of unknown, missing or invalid data for age group, race/ethnicity, and sex varies from year to year, state to state, and by disease for reported STDs (Table A1).

When the percentage of unknown, missing, or invalid data for the variables - age group, race/ethnicity, and sex - exceeds 50% for any state, the state's incidence data and population data are excluded from the tables presenting data stratified by one or more of these variables. For those states reporting > 50% valid data for these variables, unknown, missing or invalid data are redistributed based on the state's distribution of known age group, race/ethnicity, and sex data, respectively. As a result of this procedure, incidence and rate data stratified by one or more of the variables - age group, race/ethnicity, and sex - may not accurately reflect total national incidence or rates.

Classification of STD Morbidity Reporting Sources

Prior to 1996, states classified the source of case reports as either private source (including private physicians, and private hospitals and institutions) or public (clinic) source (primarily STD clinics). As states began reporting morbidity data electronically in 1996, the classification categories for source of case reports expanded to include the following data sources: STD clinics, HIV counseling and testing sites, drug treatment clinics, family planning clinics, prenatal/obstetrics clinics, tuberculosis clinics, private physicians/HMOs, hospitals (inpatient), emergency rooms, correctional facilities, laboratories, blood banks, National Job Training Program, school-based clinics, mental health providers, military, Indian Health Service, and other unspecified sources. Analysis of the data reported electronically after 1996 confirmed that the new STD clinic source of report data corresponded to the earlier reporting source category, public (clinic) source. Therefore, source of case report data for the period 1984-2006 are presented as STD clinic or non-STD clinic only (Table A2).

Definition of DHHS Regions

The ten U.S. Department of Health and Human Services (DHHS) regions referred to in the text and figures include the following jurisdictions: Region I = Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont; Region II = New Jersey, New York, Puerto Rico, and U.S. Virgin Islands; Region III = Delaware, District of Columbia, Maryland, Pennsylvania, Virginia, and West Virginia; Region IV = Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee; Region V= Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin; Region VI = Arkansas, Louisiana, New Mexico, Oklahoma, and Texas; Region VII = Iowa, Kansas, Missouri, and Nebraska; Region VIII = Colorado, Montana, North Dakota, South Dakota, Utah, and Wyoming; Region IX = Arizona, California, Guam, Hawaii, and Nevada; and Region X = Alaska, Idaho, Oregon, and Washington.

Chlamydia Morbidity Reporting

Trends in chlamydia morbidity reporting from many areas are more reflective of changes in diagnosis, screening, and reporting practices than of actual trends in disease incidence. As areas develop chlamydia prevention and control programs, including improved surveillance systems to monitor trends, the data should improve and become more representative of true trends in disease.

Syphilis Morbidity Reporting

"Total syphilis" or "all stages of syphilis" includes primary, secondary, latent (including early latent, late latent, and latent syphilis of unknown duration), neurosyphilis, late (including late syphilis with clinical manifestations other than neurosyphilis), and congenital syphilis.

In 1996, the syphilis stage, "late syphilis with clinical manifestations other than neurosyphilis (late benign and cardiovascular syphilis)", was added to the syphilis case definition (see STD Case Definitions in this Appendix).

While neurosyphilis can occur at almost any stage of syphilis, between 1996 and 2005, it was classified and reported as one of several mutually exclusive stages of syphilis. Beginning in 2005, neurosyphilis was no longer classified or reported as a distinct stage of syphilis. The Division of STD Prevention is reviewing these data collection and reporting changes to determine their impact on syphilis surveillance case definitions.

Congenital Syphilis Morbidity Reporting

In 1988, the surveillance case definition for congenital syphilis was changed. This case definition has greater sensitivity than the former definition.2 In addition, many areas have greatly enhanced active case finding for congenital syphilis since 1988. For these reasons, the number of reported cases increased dramatically during 1989-1991. All reporting areas had implemented the new case definition for reporting congenital syphilis by January 1, 1992.

In addition to changing the case definition for congenital syphilis, CDC introduced a new data collection form (CDC 73.126) in 1990 (revised October 2003). Since 1995, the data collected on this form have been used for reporting congenital syphilis cases and associated rates. This form is used to collect individual case information which allows more thorough analysis of case characteristics. For the purpose of analyses by race/ethnicity, if either the race or ethnicity question was answered, the case was included. For example, if "white" race was marked, but ethnicity was left blank, the individual was counted as "non-Hispanic white". Congenital syphilis cases were reported by state and city of residence of the mother for the period 1995 through 2006.

Chlamydia, Gonorrhea, and Syphilis Prevalence Monitoring

Chlamydia and gonorrhea test positivity and syphilis seroreactivity were calculated for the following: women attending family planning clinics and prenatal clinics, men and women entering the National Job Training Program, men attending STD clinics and primary care clinics participating in the MSM Prevalence Monitoring Project, and men and women entering corrections facilities. Positivity was calculated by dividing the number of positive tests for chlamydia, gonorrhea, or syphilis (numerator) by the total number of positive and negative tests for each disease (denominator) and was expressed as a percentage. Except for the National Job Training Program screening data, these data sources may include more than one test from the same individual if that person was tested more than once during a year.

To increase the stability of the annual National Job Training Program prevalence estimates, chlamydia or gonorrhea prevalence data are presented when valid test results for 100 or more students per year are available for the population subgroup and state. The majority of the National Job Training Program's chlamydia screening tests are tested by a single national contract laboratory which provides   those data to CDC. Gonorrhea screening tests for male and female students in many training centers are tested by local laboratories; these data are not available to CDC. To insure that state-specific gonorrhea screening data presented here are representative of all students entering training centers, gonorrhea test results for students at centers submitting specimens to the national contract laboratory are included only if the number of gonorrhea tests submitted is greater than 90% of the number of chlamydia tests submitted from the same center for the same time period.

Various laboratory test methods were used for all of these data sources except the National Job Training Program. For most of the figures presenting test positivity or prevalence data, no adjustments of test positivity based on laboratory test type and sensitivity were made. However, for Figure 10 and Figure J, the chlamydia test results for each test type were weighted to reflect the sensitivity of the test used.3 The weights used in this adjustment are the reciprocals of the sensitivities of the laboratory test methods used. These test type-specific sensitivities were estimates derived from published evaluations of chlamydia screening tests.4,5 Limitations of this adjustment include: unknown dates when laboratories changed tests, missing information on the test method, variation of test sensitivity within a technology type, and no adjustment for supplemental testing such as negative grey zone testing. For more details on chlamydia prevalence, refer to the following annual publication: Centers for Disease Control and Prevention. Sexually Transmitted Disease Surveillance 2006 Supplement: Chlamydia Prevalence Monitoring Project Annual Report 2006. Atlanta, GA: U.S. Department of Health and Human Services (available first quarter 2008).

In the MSM Prevalence Monitoring Project the syphilis seroreactivity data in most instances do not reflect confirmatory testing and thus biologic false positive test results were not systematically excluded. The extent to which these data reflect prevalence of active syphilis infection varies by site. Similarly, in the Corrections Prevalence Monitoring Project, syphilis seroreactivity test results were not confirmed. Only a few juvenile corrections sites submitted data to CDC, making overall interpretation difficult due to the small sample size. Because only selected corrections facilities participated in the Corrections Prevalence Monitoring Project, state-specific positivity for syphilis, chlamydia, and gonorrhea may not be representative of all corrections facilities in the state.

Prevalence data for region-and state-specific figures were published with permission from the Regional Infertility Prevention Program, selected state STD prevention programs, and the National Job Training Program.

Gonococcal Isolate Surveillance Project (GISP)

Data on antimicrobial susceptibility in Neisseria gonorrhoeae were collected through the Gonococcal Isolate Surveillance Project (GISP), a sentinel system of 28 STD clinics and five regional laboratories located throughout the United States. For more details on findings from GISP gonorrhea surveillance activities, refer to the following annual publication: Centers for Disease Control and Prevention. Sexually Transmitted Disease Surveillance 2006 Supplement: Gonococcal Isolate Surveillance Project (GISP) Annual Report 2006. Atlanta, GA: U.S. Department of Health and Human Services (available first quarter 2008).

Other Surveillance Data Sources

National Disease and Therapeutic Index (NDTI)

The information on the number of initial visits to private physicians' offices for sexually transmitted diseases was based on analysis of data from the National Disease and Therapeutic Index (NDTI) (machine-readable files or summary statistics for the period 1966 through 2006).The NDTI is a probability sample survey of private physicians' clinical management practices. For more information on this database, contact IMS Health, 660 W. Germantown Pike, Plymouth Meeting, PA 19462; Telephone: (800) 523-5333.

National Hospital Discharge Survey (NHDS)

The information on patients hospitalized for pelvic inflammatory disease or ectopic pregnancy was based on analysis of data from the National Hospital Discharge Survey (machine-readable files for years 1980-2005), an ongoing nation wide sample survey of medical records of patients discharged from acute care hospitals in the United States, conducted by the National Center for Health Statistics. For more information, see Graves EJ; 1988 Summary: National Hospital Discharge Survey; Advance data No. 185; Hyattsville (MD): National Center for Health Statistics, 1990.

National Hospital Ambulatory Medical Care Survey (NHAMCS-ER)

The National Hospital Ambulatory Medical Care Survey (NHAMCS-ER) (machine-readable files for 1995 - 2005) was used to obtain estimates of the number of emergency room visits for pelvic inflammatory disease among women ages 15 to 44 years. The estimates generated using these data sources (NHDS and NHAMCS-ER) are based on statistical surveys and therefore have sampling variability associated with the estimates.

Healthy People 2010 Objectives

Healthy People 20106 is a set of health objectives for the U.S. to achieve over the first decade of the new century. It is used by people, States, communities, professional organizations, and others to help develop programs to improve health. HP2010 builds on initiatives pursued over the past two decades. The 1979 Surgeon General's Report, Healthy People, and Healthy People 2000: National Health Promotion and Disease Prevention Objectives established national health objectives and served as the basis for the development of State and community plans. Like its predecessors, Healthy People 2010 was developed through a broad consultation process, built on the best scientific knowledge and designed to measure programs over time. Healthy People 2010 is organized into 28 focus areas, each with objectives and measures designed to drive action that will support two overarching goals: 1) increasing the quality and years of healthy life and 2) eliminating health disparities.

Focus area 25 of Healthy People 2010 - Sexually Transmitted Diseases, - contains objectives and measures related to STDs. The baselines, HP2010 targets and annual progress toward the targets are reported in Table A3. The year 2010 targets for the diseases addressed in this report are: primary and secondary syphilis - 0.2 case per 100,000 population; congenital syphilis - 1.0 case per 100,000 live births; and gonorrhea - 19.0 cases per 100,000 population. An additional target established in the HP2010 objectives is to reduce the Chlamydia trachomatis test positivity to 3% among females aged 15 to 24 years who attend family planning and STD clinics and among males aged 15 to 24 who attend STD clinics.

Government Performance and Results Act of 1993 (GPRA) Goals

The Government Performance and Results Act of 1993 (GPRA) was enacted by Congress to increase the confidence of citizens in the capability of the federal government, to increase the effectiveness and accountability of federal programs, to improve service delivery, to provide agencies a uniform tool for internal management and to assist Congressional decision making. GPRA requires each agency to have a performance plan with long-term outcomes and annual, measurable performance goals and to report on these plans annually, comparing results with annual goals. There are two STD GPRA goals: 1) reduction in pelvic inflammatory disease (PID) and 2) elimination of syphilis. Each of these goals has measures. The long-term goals and measures of progress are reported in Table A4.

1 Office of Management and Budget. Standards for Defining Metropolitan and Micropolitan Statistical Areas: Notice Federal Register December 27, 2000;65(249):82228-38

2 Kaufman RE, Jones OG, Blount JH, Wiesner PJ. Questionnaire survey of reported early congenital syphilis: problems in diagnosis, prevention, and treatment. Sexually Transmitted Diseases 1977;4:135-9.

3 Webster Dicker L, Mosure DJ, Levine WC,Black CM, Berman SM. The impact of switching laboratory tests on reported trends in Chlamydia trachomatis infections. Am J Epidemiol 2000;151:430-435.

4 Newhall WJ, DeLisle S, Fine D, et al.Head-to-head evaluation of five differentnon-culture chlamydia tests relative to aquality-assured culture standard. Sexually Transmitted Diseases 1994;21:S165-6.

5 Black CM, Marrazzo J, Johnson RE, et al. Head-to-head multi center comparision of DNA probe and nucleic acid amplification tests for Chlamydia trachomatis infection in women performed with an improved reference standard. J Clin Micro 2002;40:3757-3763

6 U.S. Department of Health and Human Services. Healthy People 2010 2nd ed. With Understanding and Improving Health and Objectives for Improving Health. 2 vols. Washington, DC: U.S. Government Printing Office, November 2000.

Page last modified: November 13, 2007
Page last reviewed: November 13, 2007

Content Source: Division of STD Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention