National Health and Nutrition Examination Survey

2011-2012 Data Documentation, Codebook, and Frequencies

Toxoplasma gondii Antibody - Serum (Surplus) (SSTOXO_G)

Data File: SSTOXO_G.xpt

First Published: January 2016

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 (10-<15% of records) that were initially included in error. No data values were altered. However, survey weights were newly created. For each analyte included in this data file, it was determined that overall and for stratified sex, age, and race/Hispanic origin groups, the updated file using the new sample weights resulted in an estimate within the 95% confidence limit calculated using the original file and sample weights. 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

Sera from residual specimens from NHANES 2011-2012 participants were tested for Toxoplasma gondii by an enzyme immunoassay (EIA) that detects IgG and IgM antibodies against T. gondii. The results for the Toxoplasma IgG in this data release are reported as IU/ml. Samples with results ≥ 33 IU/mL should be coded as Positive, samples with results < 27 IU/mL should be coded as Negative, and samples with results ≥ 27 IU/mL and <33 IU/mL were considered Equivocal. The Toxoplasma IgM results are reported as Ratio values. Sample Ratio < 0.8 are coded as Negative, Sample Ratio ≥ 0.8 < 1 are coded as Equivocal, and Sample Ratio ≥ 1 are coded Positive. All results originally considered Equivocal were repeated at least twice for confirmation and should be coded as Negative.

To complement the detection of anti-toxoplasma IgG and IgM the VIDAS Toxo-IgG Avidity assay was performed on the samples that coded positive for both IgG and IgM. Samples with results <20 are coded Low, samples ≥20 and <30 are coded Equivocal, and samples ≥30 are coded High.

Eligible Sample

Participants age 6+ who consented to storing their samples for future research and had stored samples from 2011-2012. As required by the NCHS ERB, Toxoplasma IgM testing was excluded for women pregnant at the time of the MEC examination and within 1 year previously.

Description of Laboratory Methodology

Toxoplasma gondii IgG and IgM antibodies were measured with two enzyme immunoassay kits (Bio-Rad, Redmond, WA). The Toxoplasma IgG EIA test utilizes antigen-coated wells. The samples are incubated in the antigen-coated wells, (if present) T. gondii antibodies are immobilized in the wells. Residual sample is eliminated by washing and conjugate (enzyme labeled antibodies to human IgG) is added and incubated. If IgG antibodies to T. gondii are present, the conjugate will be immobilized in the wells. Residual conjugate is eliminated by washing and the substrate is added. In the presence of the enzyme, the substrate is converted to a yellow end product which is read photometrically.

The Platelia Toxo IgM test utilizes an immunoenzymatic double sandwich method. The samples are incubated in the anti-human IgM coated wells. The IgM antibodies, if present, are captured by the solid phase. Remaining antibodies and residual sample are removed by washing. A solution containing T. gondii antigen and conjugate (monoclonal antibody to T. gondii labeled with HRP) is added to the wells. T. gondii IgM antibodies in the sample that are captured on the wells bind the T. gondii antigen-complex. Excess T. gondii antigen and conjugate are removed by washing and the substrate is added. In the presence of the enzyme, the substrate is converted to a yellow end product which is read photometrically.

Optical density was determined on a vMax microplate reader and computer equipped with SOFTmax software (Molecular Devices Corp., Menlo Park, CA).

Quality control samples are included on every plate. The results of serologic tests are of value as presumptive evidence of T. gondii infection. The test results are objective and normalized as index values, International Units (IU/mL), which are traceable to the WHO Anti-Toxoplasma Serum, 3rd International Standard Preparation, 1994. Prior to the study the Toxoplasma IgG EIA was evaluated using an established serum panel and comparison with the CDC Toxoplasma immunofluorescence assay and the Sabin-Feldman dye test and found to have a sensitivity and specificity of 100%.

The avidity test was performed on samples positive for both Toxoplasma IgG and IgM by Palo Alto Medical Foundation utilizing the VIDAS® TOXO IgG Avidity (TXGA) kit. The VIDAS® TOXO IgG Avidity assay is an automated qualitative test for the determination of anti-Toxoplasma IgG avidity in human serum using the ELFA technique (Enzyme Linked Fluorescent Assay). The assay is intended for use in conjunction with results from the VIDAS TOXO IgG II and must have a positive titer ≥ 8 IU/mL. Samples with an index (ratio of high avidity antibodies to total IgG antibodies; numbers represent percent) of <20 are coded as Low avidity, samples ≥20 but <30 are coded Equivocal, and samples ≥30 are coded High avidity.

Laboratory Quality Assurance and Monitoring

The Toxoplasma gondii EIA test is considered in control provided the quality control serum is within two standard deviations of its mean.

Data Processing and Editing

Data was compiled after all the antibody testing was completed. The data were not edited.

Data Access: All data are publicly available.

Analytic Notes

Results were measured as IU/ml for Toxoplasma IgG. Samples with results ≥ 33 IU/mL should be coded as Positive, samples with results < 27 IU/mL should be coded as Negative, and samples with results ≥ 27 IU/mL and <33 IU/mL were considered Equivocal. All results originally considered Equivocal were repeated at least twice for confirmation and should be coded as Negative.

Results were measured as Sample Ratio for Toxoplasma IgM. Sample Ratio < 0.8 are coded as Negative, Sample Ratio ≥ 0.8 < 1 are coded as Equivocal, and Sample Ratio ≥ 1 are coded Positive. All results originally considered Equivocal were repeated at least twice for confirmation and should be coded as Negative. Toxoplasma gondii IgM antibodies can persist for several months to years after acute infection, and false-positive tests occur, therefore Toxoplasma IgM tests have limited use in determining the timing or incidence of T. gondii infection.

Subsample Weights

Sample weights are required to analyze these data properly. Specific sample weights for this subsample are included in this data file and should be used when analyzing these data. When observations were removed from this data file, a new sample weight was created and added to this data file (WTSSTT2Y). 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.

References

Dhakal R, Gajurel K, Pomares C, Talucod J, Press CJ, Montoya JG. Significance of a positive Toxoplasma immunoglobulin M test result in the United States. J Clin Microbiol 2015;53:3601-5.
Pelloux, H. et al. Determination of anti-Toxoplasma gondii immunoglobulin G avidity: adaption to the Vidas system (bioMérieux). Diagn Microbiol Infect Dis 32: 69-73, 1998
PLATELIA™ TOXO IgM, Bio-Rad, Redmond, WA. http://www.bio-rad.com/webroot/web/pdf/inserts/CDG/en/Literature/inserts/72841_881043_GB.pdf [Accessed on: 10/22/15]
Toxoplasma IgG EIA, Bio-Rad, Redmond, WA. : http://www.bio-rad.com/webroot/web/pdf/WWMSDS/RMD/USA/USA_ENG_SDSen25175.pdf [Accessed on: 10/22/2015]
Villard O, Cimon B, L'Ollivier C, Fricker-Hidalgo H, Godineau N, Houze S, Paris L, Pelloux H, Villena I, Candolfi E. Help in the choice of automated or semiautomated immunoassays for serological diagnosis of toxoplasmosis: evaluation of nine immunoassays by the French national reference center for toxoplasmosis. J Clin Microbiol 2016;54:3034-42.
Wilson CB, Nizet VN, Maldonado Y, Remington, Klein. Toxoplasmosis. In
JS Remington, JO Klein (ed). Infectious Diseases of the Fetus and Newborn Infant, 8th ed. Philadelphia: Elsevier Saunders, 2016:949-1042. McAuley JB, Jones JL, Singh K. Toxoplasma. In: Manual of Clinical Microbiology. 11th ed. Washington DC: ASM Press; 2015.
Wilson M, JL Jones, JM McAuley. Toxoplasma. In PR Murray, EJ Baron, MA Pfaller, JH
Jorgensen, RH Yolken (ed.), Manual of Clinical Microbiology, 8th ed. American Society for Microbiology, Washington, D.C., 2003:1970-1980.
Wilson M, Remington JS, Clavet C, Varney G, Press C, Ware D, 1997. Evaluation of six commercial kits for detection of human immunoglobulin M antibodies to Toxoplasma gondii. The FDA Toxoplasmosis Ad Hoc Working Group. J Clin Microbiol 35:3112–15.

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:: SEQN
SAS Label:: Respondent sequence number
English Text:: Respondent sequence number.
Target:: Both males and females 6 YEARS - 150 YEARS

WTSSTT2Y - SSTOCA and SSTOXO 2 year weights

Variable Name:: WTSSTT2Y
SAS Label:: SSTOCA and SSTOXO 2 year weights
English Text:: Surplus specimen SSTOCA and SSTOXO 2 year weights
Target:: Both males and females 6 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
5700.578442 to 247519.73303	Range of Values	6099	6099
0	No lab specimen	0	6099
.	Missing	0	6099

SSTOXG - Toxoplasmosis IgG antibodies (IU/ml)

Variable Name:: SSTOXG
SAS Label:: Toxoplasmosis IgG antibodies (IU/ml)
English Text:: Toxoplasmosis IgG antibodies (IU/ml)
Target:: Both males and females 6 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
0 to 234	Range of Values	6097	6097
.	Missing	2	6099

SSTOXM - Toxoplasmosis IgM antibodies

Variable Name:: SSTOXM
SAS Label:: Toxoplasmosis IgM antibodies
English Text:: Toxoplasmosis IgM antibodies
Target:: Both males and females 6 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
0 to 8.1	Range of Values	5975	5975
.	Missing	124	6099

SSTOXAV - Toxoplasmosis IgG Avidity (IU/ml)

Variable Name:: SSTOXAV
SAS Label:: Toxoplasmosis IgG Avidity (IU/ml)
English Text:: Toxoplasmosis IgG Avidity (IU/ml)
Target:: Both males and females 6 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
5 to 68.6	Range of Values	38	38
.	Missing	6061	6099

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