Interpreting STD Surveillance Data

Sexually Transmitted Disease Surveillance 2009 presents surveillance information derived from the official statistics for the reported occurrence of nationally notifiable sexually transmitted diseases (STDs) 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 all 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, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, 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 hard copy reporting forms and electronic data received through the National Electronic Telecommunications System for Surveillance (NETSS).

Summary Report Forms

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

1. FORM CDC 73.998: Monthly Surveillance Report of Early Syphilis. This monthly hard copy reporting form was used during 1984–2002 to report summary data for primary and secondary syphilis and early latent syphilis by county and state.
2. FORM CDC 73.688: Sexually Transmitted Disease Morbidity Report. This quarterly hard copy reporting form was used during 1963–2002 to report summary data for all stages of syphilis, congenital syphilis, gonorrhea, chancroid, chlamydia, and other STDs by sex and source of report (private versus public) for all 50 states, the District of Columbia, 64 selected cities (including San Juan, Puerto Rico), and outlying areas of the United States.

   Note: 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 described later in this section.

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 hard copy form was used during 1981–2002 to report summary data for P&S syphilis, gonorrhea, and chlamydia by age, race, sex, and source (public versus private) for all 50 states, seven large cities (Baltimore, Chicago, New York City, Los Angeles, Philadelphia, San Francisco, and the District of Columbia), and outlying areas of the United States.

   Note: 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 Reporting. This case-specific hard copy form was first used in 1983 and continues to be used to report detailed case-specific data for congenital syphilis in some areas.

National Electronic Telecommunications System for Surveillance

Notifiable STD data reported electronically through NETSS make up the nationally notifiable disease information published in CDC’s Morbidity and Mortality Weekly Report.

As of December 31, 2003, all 50 states and the District of Columbia had converted from summary hard copy reporting to electronic submission of line-listed (i.e., case-specific) STD data through NETSS (42 reporting areas submit congenital syphilis surveillance data through NETSS). Puerto Rico converted to electronic reporting in 2006. Guam and the Virgin Islands continue to report STD data through summary hard copy forms.

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

Surveillance data and updates sent to CDC through NETSS and on hard copy forms through June 9, 2010, are included in this report. Data received after this date will appear in subsequent STD surveillance reports. The data presented in the figures and tables in this report supersede those in all earlier publications.

Population Denominators and Rate Calculations

2000–2009 Rates and Population

CDC’s National Center for Health Statistics (NCHS) released bridged-race population counts for the 2000–2008 U.S. resident populations that are based on counts from the 2000 U.S. Census. These estimates resulted from bridging the 31 race categories used in the 2000 census, as specified in the 1997 Office of Management and Budget (OMB) standards, to the five race/ethnicity groups specified in the 1977 OMB standards.

Population estimates for Guam, Puerto Rico, and the Virgin Islands were obtained from the U.S. Census Bureau Web site at https://www.census.gov/programs-surveys/popest.html. The 2008–2009 rates for outlying areas were calculated by using the 2008 population estimates.

Because of the use of the updated population data, rates for 2000–2008 may be different from those presented in previous STD surveillance reports.

1990–1999 Rates and Population

The population counts for 1990 through 1999 incorporated the bridged single-race estimates of the April 1, 2000, U.S. 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 by using U.S. Census Bureau population estimates for 1981 through 1989.^1,2

1941–1980 Rates and Population

Rates for 1941 through 1980 were based on population estimates from the U.S. Census Bureau and are currently maintained by CDC’s Division of STD Prevention.

1941–2009 Congenital Syphilis Rates and Live Births

The congenital syphilis data in Table 1 of this report represent the number of congenital syphilis cases per 100,000 live births for all years during 1941–2009. Previous publications presented congenital syphilis rates per 100,000 population during 1941–1994 and rates for cases diagnosed at younger than 1 year of age per 100,000 live births during 1995–2005. To allow for trends in congenital syphilis rates to be compared for the period 1941 through 2009, live births are used as the denominator for congenital syphilis, and case counts are no longer limited to those diagnosed within the first year of life. Congenital syphilis morbidity (i.e., case reports) is assigned by year of birth. Rates of congenital syphilis for 1963 through 1988 were calculated by using published live birth data.³ Congenital syphilis rates for 1989 through 2005 were calculated by using live birth data that are based on information coded by the states and provided to the NCHS through the Vital Statistics Cooperative Program. Rates for 2006 through 2009 were calculated by using live birth data for 2006.

Reporting Practices

Although most state and local STD programs generally adhere to the national notifiable STD case definitions collaboratively developed by the Council of State and Territorial Epidemiologists and CDC, differences in policies and systems for collecting surveillance data may exist. Thus, comparisons of case numbers and rates between jurisdictions should be interpreted with caution.

However, because case definitions and surveillance activities within a given area remain relatively stable over time, trends should be minimally affected by these differences. In many state and local STD jurisdictions, 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 Surveillance Data by Metropolitan Statistical Area

Sexually Transmitted Disease Surveillance 2009 continues the presentation of STD incidence data and rates for the 50 metropolitan statistical areas (MSAs) with the largest populations according to 2000 census data. STD surveillance reports published before 2005 presented data by selected cities; these data were derived from county data, which were used to estimate city-specific disease rates. Because county data were used to estimate city-specific morbidity and because current STD project areas’ reporting practices do not support direct identification of city-specific morbidity reports, MSAs were chosen as a geographic unit smaller than a state or territory for presentation of STD morbidity data.

MSAs are defined by the OMB to provide nationally consistent definitions for collecting, tabulating, and publishing federal statistics for a set of geographic areas.⁴ 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 central county, plus adjacent, outlying counties that have 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 the principal city with the largest 2000 census 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 links 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. STD 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 intended to be a general purpose geographic framework for nonstatistical activities or for use in program funding formulas.

For more information on the MSA definitions used in this report, go to https://www.census.gov/population/estimates/metro-city/03mfips.txt.

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

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 age group, race/ethnicity, and sex exceeds 50% for any state, the state’s incidence and population data are excluded from the tables that present data stratified by one or more of these variables. For the states for which 50% or more of their data are valid for age group, race/ethnicity, and sex, the values for unknown, missing, or invalid data are redistributed on the basis of the state’s distribution of known age group, race/ethnicity, and sex data.

As a result, incidence and rate data that are stratified by one or more of these variables may not accurately reflect total national incidence or rates.

Classification of STD Morbidity Reporting Sources

Before 1996, states classified the source of case reports as either private source (including private physicians, hospitals, and institutions) or public 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/health maintenance organizations, hospitals (inpatient), emergency rooms, correctional facilities, laboratories, blood banks, the National Job Training Program (NJTP), school-based clinics, mental health providers, the military, the 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 public source category. Therefore, source of case report data during 1984–2009 are presented as STD clinic or non-STD clinic only (Table A2).

Definition of HHS Regions

The 10 regions of the U.S. Department of Health and Human Services (HHS) 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

Trends in chlamydia morbidity reporting from many state and local jurisdictions are more reflective of changes in diagnostic, screening, and reporting practices than of actual trends in disease incidence. In particular, morbidity trends are likely to be influenced by changes in test technology as laboratories expand their use of more sensitive tests (e.g., nucleic acid amplification tests). As more jurisdictions 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

The category of “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 Surveillance Case Definitions in the Appendix). Although neurosyphilis can occur at almost any stage of syphilis, during 1996–2005, 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.

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.⁵ In addition, many state and local STD programs have greatly enhanced active case finding for congenital syphilis since 1988. For these reasons, as well as because of increasing morbidity, 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 analyzing race/ethnicity, cases are classified by the race/ethnicity of the mother. Congenital syphilis cases were reported by state and city of residence of the mother during 1995–2009.

Congenital syphilis reporting may be delayed as a result of case investigation and validation. Cases for previous years are added to CDC’s surveillance databases throughout the year. Congenital syphilis data reported after publication of the current annual STD surveillance report will appear in subsequent reports and are assigned by the case patient’s year of birth.

Chlamydia and Gonorrhea Prevalence Monitoring

Chlamydia and gonorrhea test positivity or prevalence were calculated for women visiting family planning clinics and prenatal clinics, men and women entering NJTP, and men and women entering corrections facilities. Except for the screening data from NJTP, these data sources may include more than one test from the same person if that person was tested more than once during a year.

To increase the stability of the annual prevalence estimates from NJTP, 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 NJTP’s chlamydia screening tests are conducted by a single national contract laboratory, which provides these data to CDC. Gonorrhea screening tests for male and female students in many training centers are conducted by local laboratories; these data are not available to CDC. To ensure that the state-specific gonorrhea screening data presented here are representative of all students entering training centers, test results for students at centers that submit 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 period.

Various laboratory test methods were used for all of these data sources. No adjustments for laboratory test type and sensitivity were made to any figures that present test positivity or prevalence data.

Prevalence data for region- and state-specific figures were published with permission from the Infertility Prevention Project (IPP), selected state STD prevention programs, and NJTP.

STD Surveillance Network

In 2005, CDC established the STD Surveillance Network (SSuN) as a dynamic STD surveillance network comprised of local enhanced STD surveillance systems that follow common protocols. The purpose of SSuN is to improve the capacity of national, state, and local STD programs to detect, monitor, and respond rapidly to trends in STDs through enhanced collection, reporting, analysis, visualization, and interpretation of disease information.

Twelve collaborating local or state health departments participate in SSuN: Alabama Department of Public Health, Baltimore City Health Department, Chicago Department of Public Health, Colorado Department of Public Health and Environment, Connecticut Department of Public Health, County of Los Angeles Department of Public Health (in collaboration with California State Department of Public Health), Louisiana Office of Public Health, New York City Department of Health and Mental Hygiene, Philadelphia Department of Public Health, San Francisco Department of Public Health, Virginia Department of Health, and Washington State Department of Health.

The SSuN data contained in this report include demographic, behavioral, clinical, and laboratory information collected from all patients at 42 STD clinics within the jurisdictions of SSuN health departments. These clinics are located in San Francisco, CA (San Francisco City Clinic); Los Angeles, CA (12 STD clinics in Los Angeles County); Seattle, WA (Seattle-King County Clinic); Denver, CO (Denver Metro Health Clinic); Chicago, IL (6 public STD clinics in Cook County); New Orleans, LA (Delgado Personal Health Center); Birmingham, AL (Jefferson County STD Clinic); Richmond, VA (Richmond City, Henrico County and Chesterfield County Clinics); Baltimore, MD (Druid STD Clinic and Eastern STD Clinic); Philadelphia, PA (Philadelphia STD Clinics 1 and 5); New York City, NY (10 public STD clinics in 5 boroughs); Hartford, CT (Hartford STD Clinic); and New Haven, CT (New Haven STD Clinic).

Men who have sex with men (MSM) were defined as men who either reported having sex with another man in the 3 months before STD testing (asked at all SSuN sites) or who did not report sex with men but reported that they considered themselves gay/homosexual or bisexual (asked at 8 of the 12 sites). Men who have sex with women (MSW) were defined as men who reported having sex with women only within the 3 months before STD testing or who did not report the sex of their sex partner, but reported that they considered themselves straight/heterosexual (asked at 8 of the 12 sites).

Gonococcal Isolate Surveillance Project

Data on antimicrobial susceptibility in Neisseria gonorrhoeae were collected through the Gonococcal Isolate Surveillance Project (GISP), a sentinel system of selected STD clinics located at 25–30 GISP sentinel sites and 4–5 regional laboratories in the United States. For more details on findings from GISP, go to /std/GISP.

For 2009, the antimicrobial agents tested by GISP were ceftriaxone, cefixime, cefpodoxime, azithromycin, spectinomycin, ciprofloxacin, penicillin, and tetracycline.

The antimicrobial susceptibility criteria used in GISP for 2009 are as follows:

• Ceftriaxone, minimum inhibitory concentration (MIC) ≥0.5 µg/ml (decreased susceptibility).*
• Cefixime, MIC ≥0.5 µg/ml (decreased susceptibility).*
• Cefpodoxime, MIC ≥1.0 µg/ml (decreased susceptibility).*
• Azithromycin, MIC ≥2.0 µg/ml (decreased susceptibility).*
• Spectinomycin, MIC ≥128.0 µg/ml (resistance).
• Ciprofloxacin, MIC 0.125–0.5 µg/ml (intermediate resistance).
• Ciprofloxacin, MIC ≥1.0 µg/ml (resistance).
• Penicillin, MIC ≥2.0 µg/ml (resistance).
• Tetracycline, MIC ≥2.0 µg/ml (resistance).

The majority of these criteria are also recommended by the Clinical and Laboratory Standards Institute (CLSI).⁶

Other Surveillance Data Sources

National Health and Nutrition Examination Survey

The National Health and Nutrition Examination Survey (NHANES) is a series of cross-sectional surveys designed to provide national statistics on the health and nutritional status of the general household population in the United States. Data are collected through household interviews, standardized physical examinations, and the collection of biological samples in special mobile examination centers. In 1999, NHANES became a continuous survey with data released every 2 years. The sampling plan of the survey is a stratified, multistage, probability cluster design that selects a sample representative of the U.S. civilian, noninstitutionalized population.

National Disease and Therapeutic Index

The information on the number of initial visits to private physicians’ offices for STDs was based on analysis of data from the National Disease and Therapeutic Index (NDTI) (machine-readable files or summary statistics for 1966 through 2009). 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

The information on patients hospitalized for pelvic inflammatory disease (PID) or ectopic pregnancy was based on analysis of data from the National Hospital Discharge Survey (NHDS) (machine-readable files for 1980 through 2007). NHDS, which is conducted by NCHS, is an ongoing, nationwide sample survey of medical records of patients discharged from acute care hospitals in the United States. For more information, see Graves EJ. 1988 summary: National Hospital Discharge Survey. Adv Data. 1990;185:1-11.

The estimates generated by using NHDS data are based on statistical surveys and therefore have sampling variability associated with the estimates.

Healthy People 2010 Objectives

Healthy People 2010 (HP2010) is a set of health objectives for the United States to achieve over the first decade of the new century.⁷ 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 2 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, HP2010 was developed through a broad consultation process, built on the best scientific knowledge, and designed to measure programs over time.

HP2010 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, Sexually Transmitted Diseases, contains objectives and measures related to STDs. 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 as follows: P&S 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 is to reduce the Chlamydia trachomatis test positivity to 3% among females aged 15–24 years who visit family planning and STD clinics and among males aged 15–24 years who visit STD clinics.

HP2010 targets were based on a national baseline. For most of the objectives, one target was set for all population groups to reach by the year 2010, and this target was set as a “better than the best” measure for any racial or ethnic group at the baseline.

For example, at the 1997 baseline for objective 25-2 (gonorrhea rate per 100,000 population), Asians/Pacific Islanders had the “best” rate of 20 cases per 100,000 population. Using the “better than the best” methodology resulted in the target for that objective being set at 19 per 100,000 population, even though the overall rate for the United States in 1997 was 123 cases per 100,000 population.

Government Performance and Results Act of 1993

The Government Performance and Results Act (GPRA) of 1993 was enacted by Congress to increase confidence in the capability of the federal government to increase the effectiveness and accountability of federal programs, to improve service delivery, to provide federal agencies a uniform tool for internal management, and to help Congress make decisions.

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 GPRA goals for STD: reducing PID and eliminating syphilis. Each of these goals has specific measures of progress, which are outlined in Table A4.
* The Clinical Laboratory Standards Institute criteria for decreased susceptibility and resistance to ceftriaxone, cefixime, cefpodoxime, and azithromycin and for susceptibility to azithromycin have not been established for N. gonorrhoeae.

1 U.S. Census Bureau. United States population estimates by age, sex and race: 1980–1988. In: Current population reports [Series P-25, No. 1045]. Washington, DC: U.S. Government Printing Office; 1990.

2 U.S. Census Bureau. United States population estimates by age, sex and race: 1989. In: Current population reports [Series P-25, No. 1057]. Washington, DC: U.S. Government Printing Office; 1990.

3 Centers for Disease Control and Prevention. Vital statistics of the United States 1988. vol.1 – natality. Hyattsville (MD): U.S. Department of Health and Human Services; 1990.

4 Office of Management and Budget. Standards for defining metropolitan and micropolitan statistical areas. Federal Register. 2000;65(249):82228-38.

5 Kaufman RE, Jones OG, Blount JH, Wiesner PJ. Questionnaire survey of reported early congenital syphilis: problems in diagnosis, prevention, and treatment. Sex Transm Dis. 1977;4:135-9.

6 Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing; twentieth informational supplement. M100-S20, 30(1). Wayne (PA): Clinical and Laboratory Standards Institute; 2010.

7 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; 2000.