Appendix A. Interpreting STD Surveillance Data
This web page is archived for historical purposes and is no longer being updated. Newer data is available on the STD Data and Statistics page.
Sexually Transmitted Disease Surveillance 2015 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, and national health care services 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, 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.
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 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 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 the National Electronic Telecommunications System for Surveillance (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 2015). 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 8, 2016, 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
2000–2015 Rates and Population
For those figures and tables presenting race using the 1997 OMB race standards, non-bridged-race data provided directly by the U.S. Census Bureau were used to calculate race. The latest available year for population estimates at the time this report was written was 2014. Thus, 2014 population estimates were used to calculate 2015 rates. Once published, the 2015 population estimates will be used to calculate rates in the upcoming 2016 STD Surveillance Report.
Population estimates for Puerto Rico were obtained from the U.S. Census Bureau Web site at: https://factfinder.census.gov/faces/nav/jsf/pages/index.xhtml.
Population estimates for Guam and the Virgin Islands were obtained from the U.S. Census Bureau International Programs Web site at: https://www.census.gov/data-tools/demo/idb/informationGateway.php.
The 2015 rates by age and sex for Guam and the Virgin Islands were calculated using 2010 population estimates available at: https://factfinder.census.gov/faces/nav/jsf/pages/index.xhtml.
Because of the use of the updated population data, rates for 2000–2014 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 quartiles in Figures 3, 4, 15, 16, 34, B, C, D, H, I, J, K, L, M, N, and O. Rates were grouped and displayed in 4 categories – zero cases and tertiles – in Figure 35 and Figure D.
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
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.
1941–2015 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 1941–2015. 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 2015, 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 2013 were calculated by using live birth data based on information coded by the states and provided to the NCHS through the Vital Statistics Cooperative Program. Rates for 2014 and 2015 were calculated by using live birth data for 2013.
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 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 2015 continues the presentation of STD incidence data and rates for the 50 metropolitan statistical areas (MSAs) with the largest populations according to 2010 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 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.
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/programs-surveys/metro-micro.html.
A1.5 Reporting of Data for Race/Ethnicity
In April 2008, the NETSS record layout was updated to conform to the OMB’s current government-wide standard for race/ethnicity data. The OMB standards were first issued in 1997.5 Beginning with the publication of Sexually Transmitted Disease Surveillance 2012, the race/ethnicity data are presented according to the current standard categories: American Indian or Alaska Native, Asian, Black or African American, Hispanic or Latino, Native Hawaiian/Other Pacific Islander, White and Multirace. For this report, jurisdictions are considered to be OMB compliant for a condition if ≥97% of cases for that condition are reported using current OMB standards. As of reporting year 2015, 1 jurisdiction (the District of Columbia) was not compliant with the current OMB race/ethnicity standards when reporting chlamydia and gonorrhea. Only two jurisdictions (Utah and the District of Columbia) were not compliant with the current OMB race/ethnicity standards when reporting primary and secondary syphilis.
For chlamydia and gonorrhea figures showing trends for 2011–2015, data are included for all jurisdictions except six not consistently reporting race/ethnicity data according to the current standard categories for the five consecutive years (Alaska, Maryland, Michigan, New York, North Carolina and the District of Columbia). For primary and secondary syphilis figures showing trends for 2011–2015, data are included for all jurisdictions except six not consistently reporting race/ethnicity data according to the current standard categories for the five consecutive years (Alaska, Maryland, New York, North Carolina, Utah, and the District of Columbia).
A1.6 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).
Prior to the publication of Sexually Transmitted Disease Surveillance 2010, when the percentage of unknown, missing, or invalid values for age group, race/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/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/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 2015.
As a result, rate data that are stratified by one or more of these variables reflect rates based on reported data only.
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 7, 8, 21, and 22 display trends in the proportion of cases reported in 2015 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. Expanded use of more sensitive diagnostic tests (e.g., nucleic acid amplification tests, [NAATs]) can also increase the number of infections identified and reported independent of increases in incidence. 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. Additionally, increasing use of electronic laboratory reporting has likely increased the proportion of diagnosed cases that are reported. Consequently, an increasing chlamydia case rate 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, and 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.6 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/ethnicity, cases are classified by the race/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.
A2. Other Sources of Surveillance Data
A2.1 National Job Training Program
Chlamydia and gonorrhea prevalence was calculated for men and women entering the National Job Training Program (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 L, M, N, and O.
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 areas for both core activities in SSuN Cycle 3 include Baltimore City [Maryland], California, 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 identified using non-identifying 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 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 provides estimates of case and person characteristics representative of all reported cases in the collaborating jurisdictions.
Gay, bisexual, and other men who have sex with men (collectively referred to as 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, report 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 points presented in this report for 2015 from the facility component SSuN (Figures 9, 24, 49, W, X, and Y) are based on STD clinic data from 9 SSuN jurisdictions (Baltimore City [Maryland], California, Florida, Massachusetts, Multnomah County [Oregon], New York City [New York], Philadelphia City [Pennsylvania], San Francisco County [California] and Washington State). Data presented in the report from the population component of SSuN include Figure 23, which presents data collected June through December 2015 showing the proportion of cases attributable to MSM, MSW, and women for 7 jurisdictions (Baltimore City [Maryland], California, Florida, 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 4–5 regional laboratories in the United States. For more details on findings from GISP, go to: https://www.cdc.gov/std/GISP.
For 2015, the antimicrobial agents tested by GISP were ceftriaxone, cefixime, azithromycin, ciprofloxacin, penicillin, tetracycline, and gentamicin.
The antimicrobial susceptibility criteria used in GISP for 2015 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 (decreased susceptibility)*
- 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).7
* The CLSI criteria for decreased susceptibility and resistance to ceftriaxone, cefixime, gentamicin, and azithromycin and for susceptibility to 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 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. For more information, see: https://www.cdc.gov/nchs/nhanes.htm.
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 2014; the 2015 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: ServiceCenter@us.imshealth.com; Telephone: (800) 523-5334.
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.
7 Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing; twenty-fifth informational supplement. M100-S25, 35(3). Wayne (PA): Clinical and Laboratory Standards Institute; 2015.
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