Table of Contents

Component Description

Sexually transmitted infections caused by Chlamydia trachomatis may lead to pelvic inflammatory disease, ectopic pregnancy, infertility, and chronic pelvic pain in women. They are associated with increased risk of HIV transmission. Pregnant women may transmit infection to their newborn, causing serious medical complications.

NHANES offers an opportunity to assess the prevalence of chlamydia in the general population and to monitor trends in prevalence as prevention programs are established and expanded.

Eligible Sample

Participants aged 14-39 years were tested. Public data file includes data for persons 18-39 years of age. Please see Analytic Notes about the release of data for adolescents 14-17 years of age.

Description of Laboratory Methodology

Urine specimens were processed, stored and shipped to the Division of STD Prevention Laboratory, National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention, Centers for Disease Control and Prevention for analysis. Detailed specimen collection and processing instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM).

The BDProbeTec CT Chlamydia trachomatis Amplified DNA Assays are based on the simultaneous amplification and detection of target DNA, using amplification primers and a fluorescent labeled detector probe. The Strand Displacement Amplification (SDA) reagents are dried in two separate disposable microwell strips. The processed sample is added to the Priming Microwell, which contains the amplification primers, fluorescent labeled detector probe, and other reagents necessary for amplification. After incubation, the reaction mixture is transferred to the Amplification Microwell, which contains two enzymes (a DNA polymerase and a restriction endonuclease) necessary for SDA. The Amplification Microwells are sealed to prevent contamination and then incubated in a thermally controlled fluorescent reader which monitors each reaction for the generation of amplified products. The presence or absence of C. trachomatis and N. gonorrhoeae is determined by relating the BDProbeTec ET MOTA (Method Other Than Acceleration) scores for the sample to pre-determined cutoff values. The MOTA score is a metric used to assess the magnitude of signal generated as a result of the reaction.

There were no changes (from the previous 2 years of NHANES) to equipment, lab methods or lab site.

Laboratory Quality Assurance and Monitoring

The NHANES quality assurance and quality control (QA/QC) protocols meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed quality control and quality assurance instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM). Read the General Documentation on Laboratory Data file for detailed data processing and editing protocols.

A detailed description of the quality assurance and quality control procedures can be found on the NHANES website.

Data Processing and Editing

Read the General Documentation on Laboratory Data file for detailed data processing and editing protocols. The analytical methods are described in the Analytic Notes for Data Users section below.

Public data files include data for persons 18-39 years of age. Urinary Chlamydia data for youth 14-17 years of age will only be available in the Research Data Center (RDC) or through special agreement.

Analytic Notes

The analysis of NHANES laboratory data must be conducted with the key survey design and basic demographic variables. The Demographic file contains: status variables providing core information on the survey participant including examination status, demographic variables including age, gender, race etc., and interview and examination sample weight variables and survey design variables. The Questionnaire data files contain socio-economic data, health indicators, and other related information collected during household interviews. Certain sensitive data on respondents under 18 years of age (e.g. HPV typing results, sexual behavior variables) are not included in the public use files. These data may be requested as described in the NHANES guidelines. The Phlebotomy file includes auxiliary information such as the conditions precluding venipuncture. These files may be linked to the Laboratory data file using the unique survey participant identifier SEQN.

Exam sample weights should be used for analyses. Please refer to the NHANES Analytic Guidelines  and the on-line NHANES Tutorial  for further details on the use of sample weights and other analytic issues.

Collaborators may obtain NHANES Adolescent STD Special Use Data file through a special agreement. The data set is a SAS file containing 2 variables for examined participants aged 14-17 years. Other interested researchers may use this file in the NCHS Research Data Center (RDC). The variable descriptors and variable names are as follows:

Sequence number-Seqn
Chlamydia result-URXUCL


Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:
SAS Label:
Respondent sequence number
English Text:
Respondent sequence number
Both males and females 14 YEARS - 17 YEARS

URXUCL - Urinary Chlamydia

Variable Name:
SAS Label:
Urinary Chlamydia
English Text:
Urinary Chlamydia
Both males and females 14 YEARS - 17 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Positive 11 11
2 Negative 574 585
3 Indeterminate 0 585
. Missing 22 607