Appendix A. Interpreting STD Surveillance Data

Sexually Transmitted Disease Surveillance 2018 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, Northern Mariana Islands, American Samoa, and the Virgin Islands. Selected tables and figures include data from these entities, identified as territories of the United States; however, the majority of national case counts and rates exclude data from these territories.

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) and via HL7 messaging using National Electronic Disease Surveillance System (NEDSS) standards.

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 territories of the United States.

    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 territories of the United States.

    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

As of December 31, 2003, all 50 states and the District of Columbia converted from summary hard copy reporting to electronic submission of line-listed (i.e., case-specific) data for chlamydia, gonorrhea, syphilis, and chancroid through NETSS. Though most of these areas report congenital syphilis and syphilitic stillbirths electronically, nine areas relied upon hard copy forms for reporting congenital syphilis and syphilitic stillbirths in 2018. Puerto Rico converted to electronic reporting in 2006 for all STDs, excluding congenital syphilis. American Samoa, Guam, Northern Mariana Islands, and the Virgin Islands continue to report STD data through summary hard copy forms.

Surveillance data sent to CDC through NETSS and on hard copy forms through June 19, 2019 are included in this report. The data presented in the figures and tables in this report supersede those in all earlier publications.

National Electronic Disease Surveillance System

In 2018, jurisdictions had the ability to transmit STD case notifications to CDC via HL7 messaging using NEDSS standards. Surveillance data sent to CDC via HL7 messaging from three jurisdictions (Connecticut, Idaho, and Oregon) are included in this report.

A1.2 Population Denominators and Rate Calculations

2000–2018 Rates and Population

For those figures and tables presenting race using the 1997 Office of Management and Budget (OMB) standards, nonbridged-race data provided directly by the United States Census Bureau were used to calculate rates. The latest available year for population estimates at the time this report was written was 2017. Thus, 2017 population estimates were used to calculate 2018 rates.

Once published, the 2018 population estimates will be used to calculate 2018 rates in Sexually Transmitted Disease Surveillance 2019.

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

Population estimates for American Samoa, Guam, Northern Mariana Islands, and the Virgin Islands were obtained from the US Census Bureau International Programs Web site at: icon.

The 2018 rates by age and sex for American Samoa, Guam, Northern Mariana Islands, and the Virgin Islands were calculated using the latest population estimates available at: icon.

Because of the use of the updated population data, rates for 2000–2017 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, A, C, 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.

1941–2018 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 1941–2018. 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 2018, 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 2018 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 2018 were calculated by using live birth data for 2016.

2010–2018 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 (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 (2013–2017).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. State-level estimates are then aggregated from the county-specific estimates.

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.

Data collection for chlamydia began in 1984 and chlamydia was made nationally notifiable in 1995; however, chlamydia was not reportable in all 50 states and the District of Columbia until 2000. Data collection for gonorrhea, syphilis, and chancroid began in 1941; however, gonorrhea, syphilis, and chancroid became nationally notifiable in 1944. For more information on nationally notifiable conditions, please refer to the National Notifiable Disease Surveillance System
(NNDSS) website:

A1.4 Reporting of Surveillance Data by Geographic Areas

Metropolitan statistical area

Sexually Transmitted Disease Surveillance 2018 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: icon.


Figures 4, 17, and 38 show county-level maps with rates of reported cases of chlamydia, gonorrhea, and P&S syphilis, respectively. Such county-level maps can be produced through NCHHSTP AtlasPlus, an interactive tool that allows users to create customized tables, maps, and charts using over 15 years of CDC’s surveillance data on HIV, viral hepatitis, STD, and tuberculosis. Through the Map function, users can create custom maps to observe trends in the number of cases or rates of specific STDs by state or county. For more information on county-level rates, 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 2018, 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 2018.

For this report, all race/Hispanic ethnicity data reported by jurisdictions are summarized in tables, charts, and interpretative text regardless of local compliance with the 1997 OMB standards. 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/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 with missing/unknown race and Hispanic ethnicity.

Figures T, V, and X show rate ratios by race/Hispanic ethnicity and region. Rate ratios are calculated as the rate of reported gonorrhea cases per 100,000 for a given racial or ethnic minority population divided by the rate of reported gonorrhea cases per 100,000 population for Whites. Any population with a lower rate of reported cases of gonorrhea than the White population will have a rate ratio of less than 1:1.

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 2018.

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/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 2018 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 Rates of Reported Cases of Chlamydia

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 surveillance case definition for syphilis has changed over time. Beginning in 2018, the category of “total syphilis” or “all stages of syphilis” includes: primary, secondary, early non-primary non-secondary, unknown duration or late, congenital syphilis, and syphilitic stillbirth. However, in previous years, “total syphilis” or “all stages of syphilis” have included different case classifications. For example, in the 1990 syphilis case definition, “total syphilis” or “all stages of syphilis” included: primary, secondary, latent, early latent, late latent, latent unknown duration, neurosyphilis, syphilitic stillbirth, and congenital syphilis. See Section C1.4 in the Appendix for information on current syphilis case definitions. More information on syphilis case definition changes over time can be found at:

A1.10 Congenital Syphilis Morbidity Reporting

In 1988, the surveillance case definition for congenital syphilis was changed, resulting in a more sensitive definition.11 At the same time, many state and local STD programs began to greatly enhance active case finding for congenital syphilis. These surveillance changes, in addition to rising morbidity, led to a dramatic increase in the number of congenital syphilis cases reported during 1989–1991. By January 1, 1992, the new congenital syphilis case definition was fully implemented by all reporting areas. In addition to changing the case definition, CDC introduced a new congenital syphilis data collection form (CDC 73.126) in 1990; this was later revised in February 2013. Since 1995, congenital syphilis cases are reported by state and city of residence of the mother and by the reported race/Hispanic ethnicity 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 infant’s year of birth.

A1.11 Interpreting Surveillance Data from Territories

There are a number of issues affecting the STD surveillance data reported to CDC from the US territories, 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.

In figures showing rates for US states and territories (Figures 3, 16, 37, A, C, I, J, K, L, M, and N), 2018 data from the Virgin Islands were not included as full data were not able to be obtained in time to include them in this report.

Data from American Samoa, Guam, and Northern Mariana Islands were not included in Figures O, P, Q, and R, as they do not participate in the NJTP.

In Figure AA, data from American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and the Virgin Islands were not available.

A2. Other Sources of Surveillance Data

A2.1 National Job Training Program

Chlamydia and gonorrhea prevalence was calculated for males and females 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 common 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 data collection, reporting, analysis, visualization, and interpretation of disease information.

Cycle 3 (2013–2018) of SSuN provided funding to 10 jurisdictions to conduct two core sentinel and enhanced STD surveillance activities. SSuN Cycle 3 sentinel surveillance activities included abstraction of clinical and demographic information on a full census of patients attending 30 STD clinics, and, through June 2018, among women 15–44 years of age presenting for care in facilities that provide family planning and reproductive health services. SSuN Cycle 3 enhanced surveillance activities included conducting health department registry matching, as well as provider and patient investigations on a probability sample of all persons diagnosed and reported with gonorrhea. Funded jurisdictions for 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 components of SSuN Cycle 3, unique persons (diagnosed and reported with gonorrhea or seeking care in participating clinical facilities) were longitudinally followed using unique, coded IDs to provide information on repeat infections and/or care seeking behaviors. The primary unit of analysis for sentinel surveillance activities in clinical facilities is unique persons. These data are merged with multiple laboratory, diagnostic, and treatment observations to provide a comprehensive picture of services and diagnoses received for each individual patient. For enhanced, case-based surveillance activities in SSuN Cycle 3, the primary unit of analysis is a diagnosed and reported episode (case) of gonorrhea from any provider type or setting within the funded jurisdiction. Case data also included a unique person identifier, which allowed merging with multiple laboratory observations, matching with other health department disease registries, querying provider-based clinical information, and unique patient demographic and behavioral data obtained through direct patient interviews. For analysis in the population component, cases in the probability sample were weighted to reflect study design and to adjust for non-response by demographic category of the patient. Weighted analysis provides estimates of case-level and person-level characteristics representative of all reported cases in the funded jurisdictions.

MSM are defined in all SSuN data collection activities as men who: a) reported having sex with another man in the preceding 2–3 months, and/or, b) 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 exclusively, or who did not report the sex of their sex partners but reported that they considered themselves to be straight/heterosexual.

Data presented in figures in this report from the sentinel surveillance component of SSuN Cycle 3 include data from nine of the 10 participating jurisdictions (Baltimore [Maryland], Miami [Florida], Boston [Massachusetts], Minneapolis [Minnesota], Multnomah County [Oregon], New York City [New York], Philadelphia [Pennsylvania], San Francisco [California], and Seattle [Washington]), except for Figure GG which includes data from the seven jurisdictions which provided data on P&S syphilis diagnoses (Baltimore [Maryland], Miami [Florida], Minneapolis [Minnesota], Multnomah County [Oregon], New York City [New York], San Francisco [California], and Seattle [Washington]).

Data presented in figures in this report from the population component of SSuN Cycle 3 for 2018 include gonorrhea cases sampled from all funded jurisdictions. Trend data across previous cycles of SSuN (Figure 26) include only those jurisdictions participating in both Cycles 2 and 3 (Baltimore, California [excluding San Francisco], Philadelphia, New York City, San Francisco 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 2018, the antimicrobial agents tested by GISP were ceftriaxone, cefixime, azithromycin, ciprofloxacin, penicillin, tetracycline, and gentamicin.

The antimicrobial susceptibility criteria used in GISP for 2018 are as follows:

  • Ceftriaxone, minimum inhibitory concentration (MIC) ≥0.5 μg/ml (decreased susceptibility)*
  • Ceftriaxone, MIC ≥0.125 μg/ml (elevated MIC)*
  • Cefixime, MIC ≥0.5 μg/ml (decreased susceptibility)*
  • Cefixime, MIC ≥0.25 μg/ml (elevated MIC)*
  • Azithromycin, MIC ≥2.0 μg/ml (elevated MIC)*
  • 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

* As of December 2018, the CLSI criteria for resistance to ceftriaxone, cefixime, gentamicin, and azithromycin and for susceptibility to azithromycin and gentamicin 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. 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.

4. American Community Survey. 5-year summary file, 2013–2017. US Census Bureau: 2018.

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

11. Kaufman RE, Jones OG, Blount JH, et al. Questionnaire survey of reported early congenital syphilis: Problems in diagnosis, prevention, and treatment. Sex Transm Dis. 1977;4(4):135–139.

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