Table of Contents

Component Description

Sera from residual specimens from NHANES 2013-2014 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 2013-2014. 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.

References

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

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 239 Range of Values 6599 6599
. Missing 1 6600

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
0.1 to 6.8 Range of Values 6424 6424
. Missing 176 6600

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
2.9 to 71 Range of Values 48 48
. Missing 6552 6600