Appendix A. Interpreting STD Surveillance Data

Sexually Transmitted Disease Surveillance 2017 presents surveillance information derived from the official statistics for the reported occurrence of nationally notifiable STDs in the United States, including data from sentinel surveillance and national surveys.

A1. 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, United States 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.

A1.1 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 (P&S) 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 1995 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 1995, 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 (41 reporting areas submitted congenital syphilis surveillance data through NETSS in 2017). Puerto Rico converted to electronic reporting in 2006 for all STDs excluding congenital syphilis. Guam and the Virgin Islands continue to report STD data through summary hard copy forms.

Surveillance data and updates sent to CDC through NETSS and on hard copy forms through June 19, 2018, are included in this report. The data presented in the figures and tables in this report supersede those in all earlier publications.

A1.2 Population Denominators and Rate Calculations

2000–2017 Rates and Population

For those figures and tables presenting race using the 1997 Office of Management and Budget (OMB) standards, non-bridged-race data provided directly by the United States Census Bureau were used to calculate race. The latest available year for population estimates at the time this report was written was 2016. Thus, 2016 population estimates were used to calculate 2017 rates.

Once published, the 2017 population estimates will be used to calculate 2017 rates in Sexually Transmitted Disease Surveillance 2018.

Population estimates for Puerto Rico were obtained from the US Census Bureau Web site at: https://factfinder.census.govExternal.

Population estimates for Guam and the Virgin Islands were obtained from the US Census Bureau International Programs Web site at:

The 2017 rates by age and sex for Guam and the Virgin Islands were calculated using the latest population estimates available at:

Because of the use of the updated population data, rates for 2000–2016 may be different from those presented in previous STD surveillance reports.

Several figures throughout this report depict state- or county-specific rates of reported cases of STDs. Rates were grouped and displayed by quintiles in Figures 3, 4, 16, 17, 37, E, F, I, J, K, L, M, N, O, P, Q, R, and AA. Rates were grouped and displayed in 4 categories – zero cases and tertiles – in Figure 38.

1990–1999 Rates and Population

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

1981–1989 Rates and Population

Rates were calculated by using US 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 US Census Bureau and are currently maintained by CDC’s Division of STD Prevention.

1941–2017 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 1941–2017. 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 of 1941 through 2017, live births now 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 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 2016 were calculated by using live birth data based on information coded by the states and provided to the National Center for Health Statistics (NCHS) through the Vital Statistics Cooperative Program. Rates for 2017 were calculated by using live birth data for 2016.

2010–2017 Gay, Bisexual, and Other Men Who Have Sex with Men Rates and Population

Figures 26 and AA show rates of reported cases of gonorrhea and P&S syphilis among gay, bisexual, and other men who have sex with men (collectively referred to as MSM). Population estimates of MSM are based on a method that combines published estimates of the prevalence of same-sex behavior among adult men with housing and population data from the American Community Survey 5-year summary file (2012–2016).4-7 County-specific estimates begin with MSM prevalence estimates that are determined by their urbanicity according to the NCHS urban-rural classification scheme for counties and their United States region.8 Estimates are then multiplied by a modified ratio of each county’s percentage of male same-sex households to the total percentage of male same-sex households among all counties at the same level of urbanicity and within the same region. Thus, the final estimate for each county reflects what would be expected based on the county’s geography, urban-rural classification, and observed concentration of households with a male head of household and a male partner.

A1.3 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 (CSTE) 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.

A1.4 Reporting of Surveillance Data by Metropolitan Statistical Area

Sexually Transmitted Disease Surveillance 2017 continues the presentation of STD incidence data and rates for the 50 metropolitan statistical areas (MSA) with the largest populations according to 2010 United States census 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.9 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 2010 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.

Reported cases are assigned to MSAs based on the reported county; cases reported with a missing a value for the county variable cannot be assigned to an MSA. Consequently, if a jurisdiction reports cases missing values for the county variable, reported rates for MSAs in their jurisdiction may be incomplete. Additionally, relative rankings of case counts by counties may be impacted by completeness of the variable used to identify county. Table A1 reports the percentage of cases reported with missing county information in each state for P&S syphilis, chlamydia, and gonorrhea.

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:

A1.5 Reporting of Data for Race/Hispanic Ethnicity

In April 2008, the NETSS record layout was updated to conform to the OMB’s current government-wide standard for race/Hispanic ethnicity data. The OMB standards were first issued in 1997.10 Beginning with the publication of Sexually Transmitted Disease Surveillance 2012, the race/Hispanic ethnicity data are presented according to the current OMB standard categories: American Indian or Alaska Native, Asian, Black or African American, Hispanic or Latino, Native Hawaiian or Other Pacific Islander, White, and Multirace. As of 2017, most reporting jurisdictions are locally compliant with current OMB standards and report in the current OMB standard race categories, including Multirace. However, a small number of jurisdictions reported race in pre-1997 single race categories; while other jurisdictions were using current OMB standards categories but were unable to report more than one race per person in 2017.

For this report, all race and Hispanic ethnicity data reported by jurisdictions are summarized in tables, charts, and interpretative text regardless of local compliance with the 1997 OMB standards. However, a small number of cases reported in the legacy ‘Asian/Pacific Islander’ category from non-compliant jurisdictions are re-coded to ‘Unknown’ because these cases cannot be properly re-coded into an appropriate current OMB standards category of ‘Asian’ or ‘Native Hawaiian/Other Pacific Islander.’ No redistribution of cases is done; cases missing race and/or Hispanic ethnicity are not included in the calculation of rates by race and Hispanic ethnicity. As a consequence, rate data presented in this report underestimate actual case incidence in these population categories by a roughly similar proportion to the overall percentage of cases missing/unknown race and Hispanic ethnicity.

All states and reporting jurisdictions are encouraged to continue efforts to upgrade local surveillance systems to be fully compliant with OMB standards for the collection of race and Hispanic ethnicity, to redouble efforts to ascertain complete information for all cases, and to implement CDC’s HL7 case reporting guides at the earliest opportunity.

A1.6 Management of Unknown, Missing, or Invalid Data for Age Group, Race/Hispanic Ethnicity, and Sex

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

Prior to the publication of Sexually Transmitted Disease Surveillance 2010, when the percentage of unknown, missing, or invalid values for age group, race/Hispanic ethnicity, and sex exceeded 50% for any state, the state’s incidence and population data were excluded from the tables that presented data stratified by one or more of these variables. For the states for which 50% or more of their data were valid for age group, race/Hispanic ethnicity, and sex, the values for unknown, missing, or invalid data were redistributed on the basis of the state’s distribution of known age group, race/Hispanic ethnicity, and sex data. Beginning with the publication of Sexually Transmitted Disease Surveillance 2010, redistribution methodology is not applied to any of the data. The counts presented in this report are summations of all valid data reported in reporting year 2017.

As a result, rate data that are stratified by one or more of these variables reflect rates based on reported data only; caution should be used in interpreting specific rate data points as these may underestimate reported case incidence by race and Hispanic ethnicity due to the exclusion of cases missing these important demographic data.

A1.7 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 (HMOs), 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. Figures 9, 10, 23, and 24 display trends in the proportion of cases reported in 2017 categorized by reporting source. Categories displayed vary across these figures and include the five most commonly reported sources for the population included in the figure, along with trends for all other reporting sources combined into the “All Other” category, and trends in the proportion of cases with unknown reporting source.

A1.8 Interpreting Chlamydia Case Reporting

Trends in rates of reported cases of chlamydia are influenced by changes in incidence of infection, as well as changes in diagnostic, screening, and reporting practices. As chlamydial infections are usually asymptomatic, the number of infections identified and reported can increase as more people are screened even when incidence is flat or decreasing. During 2000–2011, the expanded use of more sensitive diagnostic tests (e.g., nucleic acid amplification tests [NAATs]) likely increased the number of infections identified and reported independently of increases in incidence. Also, although chlamydia has been a nationally notifiable condition since 1994, it was not until 2000 that all 50 states and the District of Columbia required reporting of chlamydia cases. National case rates prior to 2000 reflect incomplete reporting. The increased use of electronic laboratory reporting over the last decade or so also likely increased the proportion of diagnosed cases reported. Consequently, an increasing chlamydia case rate over time may reflect increases in incidence of infection, screening coverage, and use of more sensitive tests, as well as more complete reporting. Likewise, decreases in chlamydia case rates may suggest decreases in incidence of infection or screening coverage.

A1.9 Syphilis Morbidity Reporting

The category of “total syphilis” or “all stages of syphilis” includes primary syphilis, secondary syphilis, early latent syphilis, late latent syphilis, late syphilis with clinical manifestations (including late benign syphilis and cardiovascular syphilis), and congenital syphilis.

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.

A1.10 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.11 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 February 2013). 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/Hispanic ethnicity, cases are classified by the race/Hispanic ethnicity of the mother. Similarly, since 1995, congenital syphilis cases are reported by state and city of residence of the mother.

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.

A1.11 Interpreting Surveillance Data from Outlying Areas

There are a number of issues affecting the STD surveillance data reported to CDC from the US outlying areas, including test kit stock-outs, resulting in an inability to test or screen for undetermined periods of time, as well as a variety of data collection, entry, and transmission issues. As such, the data likely underestimate the total STD burden in these areas and should be interpreted cautiously.

A2. Other Sources of Surveillance Data

A2.1 National Job Training Program

Chlamydia and gonorrhea prevalence was calculated for men and women entering the NJTP. To increase the stability of the 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 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. 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. Prevalence data for state-specific figures were published with permission from the Department of Labor. Prevalence data are presented in Figures O, P, Q, and R.

A2.2 STD Surveillance Network

In 2005, CDC established the STD Surveillance Network (SSuN) as a collaborative network of state, county and/or city health departments following protocols to conduct sentinel and enhanced STD surveillance activities. The purpose of SSuN is to improve the capacity of national, state and local STD programs to detect, monitor, and respond to trends in STDs through enhanced collection, reporting, analysis, visualization, and interpretation of disease information.

Cycle 3 (2013–2018) of SSuN provides funding to 10 jurisdictions to conduct two core STD surveillance activities including; (1) sentinel facility component, providing clinical and demographic information on a full census of patients attending categorical STD clinics and women aged 15–44 years presenting for care in reproductive health settings, and, (2) population component, conducting enhanced health department look-back, provider, and patient investigations on a probability sample of all persons diagnosed and reported with gonorrhea. Funded jurisdictions for both core activities in SSuN Cycle 3 include Baltimore City (Maryland), California (excluding San Francisco County), Florida, Massachusetts, Minnesota, Multnomah County (Oregon), Philadelphia City (Pennsylvania), New York City (New York), San Francisco County (California), and Washington State.

In both the facility and population components of SSuN Cycle 3, unique patients can be anonymously followed using unique, coded IDs to provide longitudinal information. In the facility component, the primary unit of analysis is the patient visit, which is merged with multiple laboratory, diagnostic, and treatment observations. In the population component, the primary unit of analysis is a reported episode of gonorrhea for a unique person merged with multiple laboratory observations, health department disease registry history, provider-based clinical information, and patient demographic and behavioral interview data. For analysis in the population component, cases in the probability sample are weighted to reflect study design and to adjust for non-response by demographic category of the patient. Weighted analyses provide estimates of case and person characteristics representative of all reported cases in the collaborating jurisdictions.

MSM are defined in all SSuN data collection activities as men who either reported having sex with another man in the preceding 2–3 months, reported current history of male sex partners, and/or those who reported that they considered themselves gay/homosexual or bisexual. Men who have sex with women (MSW) are defined as men who reported having sex with women only or who did not report the sex of their sex partners but reported that they considered themselves to be straight/heterosexual.

Data presented in this report from the facility component of SSuN are from nine participating jurisdictions (Baltimore City [Maryland], California [excluding San Francisco County], Massachusetts, Minnesota, Multnomah County [Oregon], New York City [New York], Philadelphia City [Pennsylvania], San Francisco County [California] and Washington State). Figures 13, 27, DD, EE, FF, and GG are based on STD clinic data and Figure G is based on data from facilities that provide family planning and reproductive health services. Data presented in this report from the population component of SSuN include Figures 25 and 26. Figure 25 presents data collected January–December 2017 showing the proportion of cases attributable to MSM, MSW, and women for all ten SSuN jurisdictions. Figure 26 presents data collected January 2010–June 2013 and June 2015–December 2017 for six SSuN jurisdictions collaborating in both SSuN Cycle 2 and SSuN Cycle 3 (Baltimore City [Maryland], California [excluding San Francisco County], New York City [New York], Philadelphia City [Pennsylvania], San Francisco County [California], and Washington State).

A2.3 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 regional laboratories in the United States. For more details on findings from GISP, go to:

For 2017, the antimicrobial agents tested by GISP were ceftriaxone, cefixime, azithromycin, ciprofloxacin, penicillin, tetracycline, and gentamicin.

The antimicrobial susceptibility criteria used in GISP for 2017 are as follows:

  • Ceftriaxone, minimum inhibitory concentration (MIC) ≥0.5 μg/ml (decreased susceptibility)*
  • Ceftriaxone, MIC ≥0.125 μg/ml (elevated MICs)*
  • Cefixime, MIC ≥0.5 μg/ml (decreased susceptibility)*
  • Cefixime, MIC ≥0.25 μg/ml (elevated MICs)*
  • Azithromycin, MIC ≥2.0 μg/ml (elevated MICs)*
  • Ciprofloxacin, MIC ≥1.0 μg/ml (resistance)
  • Ciprofloxacin, MIC 0.125–0.5 μg/ml (intermediate resistance)
  • Penicillin, MIC ≥2.0 μg/ml (resistance)
  • Tetracycline, MIC ≥2.0 μg/ml (resistance)
  • Gentamicin (MIC values correlated with susceptibility and resistance have not been established)*

The majority of these criteria are also recommended by the Clinical and Laboratory Standards Institute (CLSI).12

* The CLSI criteria for decreased susceptibility and resistance to ceftriaxone, cefixime, gentamicin, and azithromycin and for susceptibility to gentamicin and azithromycin have not been established for N. gonorrhoeae.

A2.4 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 two years. The sampling plan of the survey is a stratified, multistage, probability cluster design that selects a sample representative of the United States civilian, non-institutionalized population. For more information, see:

A2.5 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 2016; the 2017 NDTI data were not obtained in time to include them in this report). NDTI is a probability sample survey of private physicians’ clinical management practices. For more information on this database, contact IMS Health, e-mail:; Telephone: (800) 523–5334.


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

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10. Office of Management and Budget. Revisions to the Standards for Classification of Federal Data on Race and Ethnicity. Federal Register Notice. October 30, 1997.

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