National Health and Nutrition Examination Survey

2015-2016 Data Documentation, Codebook, and Frequencies

Chlamydia Pgp3 (plasmid gene product 3) ELISA (enzyme linked immunosorbent assay) and multiplex bead array (MBA) results (SSCT_I)

Data File: SSCT_I.xpt

First Published: May 2020

Last Revised: April 2022

Note: The NHANES Biospecimen Program processes were reevaluated in 2021 and 2022 to monitor quality control after a procedural error was identified. This error did not pose any risk of participant disclosure. Addressing this error resulted in the removal of some records from various stored biospecimen data files between 1999 and 2018 that did not meet program standards. After a comprehensive review of all stored specimen datasets, this data file was modified to remove records (<5% of records) that were initially included in error. No data values were altered. The sample weights and overall estimates were compared between the original and revised files. The sample weights provided with the original data release are appropriate to use with this updated data file; therefore, no new survey weights were created. The overall estimates from these files were examined and are consistent with the previous file. However, not all possible analyses were performed. For any queries related to this dataset please email the Biospecimen Program at serumplasmaurine@cdc.gov.

Component Description

Chlamydia serologic assays can be used to identify women who have been exposed to chlamydia infection. Antibodies to Pgp3 (plasmid gene product 3) have been shown to have high sensitivity^1,2 and remain positive for an extended time period.^3,4 These assays have been used to characterize prior Chlamydia trachomatis infection in nationally representative data⁵. For female NHANES participants who had a chlamydia nucleic acid antigen test (NAAT) performed from 2013 through 2016, and agreed to submit a serologic specimen, we performed Pgp3 chlamydia ELISA (enzyme linked immunosorbent assay) and Pgp3 multiplex bead array (MBA) tests to determine chlamydia seropositivity. Excluding test error (false positives and false negatives), specimens with a positive test indicate previous exposure to C. trachomatis that generated an antibody response.

Eligible Sample

Available sera from women 14-39 years old with documented chlamydia NAAT tests participating in the 2015-2016 NHANES cycles were analyzed with the Pgp3 ELISA assay and the Pgp3 MBA assay.

Data for the 14-17-year-old women will be available in the NCHS Research Data Center, https://www.cdc.gov/rdc/index.htm.

Description of Laboratory Methodology

The Laboratory Reference and Research Branch (LRRB) in the Division of STD Prevention, at the Centers for Disease Control and Prevention, performed the Pgp3 MBA and the Pgp3 ELISA assays on all 2,201 pristine 2013-2016 serologic specimens received from the National Center for Health Statistics (NCHS).

Prior to the study, positive and negative cutoffs for the Pgp3 MBA and the Pgp3 ELISA assays were established by testing a receiver operating characteristic (ROC) panel on Pgp3 coupled beads (for the Pgp3 MBA) and Pgp3 coated plates (for the Pgp3 ELISA). Readings greater than the determined cutoff of 551 median fluorescence intensity (MFI) units for the Pgp3 MBA and the normalized absorbance value of 0.303 at 450 nm for Pgp3 ELISA are considered positive and values equal to or below these cutoffs are negative. Assays were run according to standardized protocols for the Pgp3 dual ELISA assay and Luminex MAGPIX MBA assay. All results were quality checked and summarized in the accompanying data file.

Laboratory Quality Assurance and Monitoring

Serum specimens were received and accessioned by LRRB in the Division of STD Prevention. After being accessioned, the specimens were stored in −80°C freezers until assaying.

Prior to assaying the specimens, the Pgp3 ELISA assay and Pgp3 MBA assay were verified in-house by LRRB. After assays were verified, the 2013-2016 serum specimens were analyzed by both the Biotech absorbance reader for the Pgp3 ELISA assay and the MAGPIX Luminex MBA system for the Pgp3 MBA assay. Pgp3 ELISA serologies were performed in duplicate while the Pgp3 MBA assay was performed in singlet.

ELISA absorbance values from the Biotech reader were normalized by LRRB staff, averaged, and entered into spreadsheets. MBA MFI absorbance values from the MAGPIX Luminex MBA system were also entered into spreadsheets. All values entered into laboratory spreadsheets were single-entered and double-checked by LRRB staff. Monthly, we reviewed each cumulative variable in the datasets and corrected any data that were incorrect.

In the event that the lab absorbance reading was unreadable or an instrument error occurred the first time, the MBA sample was rerun one time and the value of the second reading was used as the result. For the ELISA, if an error occurred the sample was rerun in duplicate once and the average of the two repeat readings was used to calculate finalized values. Finalized individual absorbance results were tabulated and provided to NCHS.

References

Horner P. Can Chlamydia Serology Be Used to Help Inform a Potential Future Chlamydia Vaccination Strategy? Sexually transmitted diseases 2017;44:722-4.
Horner PJ, Wills GS, Reynolds R, et al. Effect of time since exposure to Chlamydia trachomatis on chlamydia antibody detection in women: a cross-sectional study. Sexually transmitted infections 2013;89:398-403.
Horner PJ, Wills GS, Righarts A, et al. Chlamydia trachomatis Pgp3 Antibody Persists and Correlates with Self-Reported Infection and Behavioural Risks in a Blinded Cohort Study. PloS one 2016;11:e0151497.
Wills GS, Horner PJ, Reynolds R, et al. Pgp3 antibody enzyme-linked immunosorbent assay, a sensitive and specific assay for seroepidemiological analysis of Chlamydia trachomatis infection. Clinical and vaccine immunology : CVI 2009;16:835-43.
Woodhall SC, Wills GS, Horner PJ, et al. Chlamydia trachomatis Pgp3 Antibody Population Seroprevalence before and during an Era of Widespread Opportunistic Chlamydia Screening in England (1994-2012). PloS one 2017;12:e0152810.

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:: SEQN
SAS Label:: Respondent sequence number
English Text:: Respondent sequence number.
Target:: Females only 18 YEARS - 39 YEARS

SSCTEIA - Chlamydia Pgp3 ELISA

Variable Name:: SSCTEIA
SAS Label:: Chlamydia Pgp3 ELISA
English Text:: Chlamydia Pgp3 ELISA
Target:: Females only 18 YEARS - 39 YEARS

Code or Value	Value Description	Count	Cumulative
0	Negative	503	503
1	Positive	304	807
.	Missing	0	807

SSCTMBA - Chlamydia Pgp3 MBA

Variable Name:: SSCTMBA
SAS Label:: Chlamydia Pgp3 MBA
English Text:: Chlamydia Pgp3 MBA
Target:: Females only 18 YEARS - 39 YEARS

Code or Value	Value Description	Count	Cumulative
0	Negative	530	530
1	Positive	277	807
.	Missing	0	807

SSCTEIOD - Chlamydia Pgp3 EIA Optical Density

Variable Name:: SSCTEIOD
SAS Label:: Chlamydia Pgp3 EIA Optical Density
English Text:: Chlamydia Pgp3 EIA Optical Density
Target:: Females only 18 YEARS - 39 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
-1.037151703 to 9.7881619938	Range of Values	807	807
.	Missing	0	807

SSCTMBFI - Chlamydia Pgp3 MBA medium fluorest inten

Variable Name:: SSCTMBFI
SAS Label:: Chlamydia Pgp3 MBA medium fluorest inten
English Text:: Chlamydia Ppg3 MBA medium fluorescence intensity
Target:: Females only 18 YEARS - 39 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
9 to 59392	Range of Values	807	807
.	Missing	0	807

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