Cytomegalovirus (CMV) is a herpesvirus, which can be a serious pathogen in infants and adults. CMV usually does not cause significant disease in healthy individuals, but pregnant women can transmit CMV to their unborn babies, who are then at risk. Congenital CMV infection is a significant source of morbidity among children, causing a wide range of clinical outcomes including jaundice, hydrocephalia, hearing loss, ocular lesions, and even death. Currently, about one out of every 200 babies are born with congenital CMV infection each year.
In the United States, one in three children are already infected with CMV by age five. Young children with CMV infection shed the virus in high titers and are a major source of transmission to other susceptible children and adults, which is of special concern for pregnant women. For this reason, characterizing infection among children less than 6 years old is essential to expanding our understanding of important transmission exposures, mainly breastfeeding and close contact during childcare, and patterns of primary and recurrent infections. Such information would inform the development of prevention strategies to protect vulnerable populations, including pregnant women and their fetuses.
Additionally, young children have been identified as a potential target population for CMV vaccine development, recently ranked of highest priority by the Institute of Medicine. Describing the serological profile of children under the age of 6 would improve our understanding of immunity during early childhood and facilitate vaccine development.
Examined participants aged 1 to 5 years were eligible.
CMV Immunoglobulin G (IgG) antibodies are detected by enzyme-linked fluorescent immunoassay (ELFA) in a semiquantitative-automated manner, using the VIDAS CMV method designed by Biomerieux. All NHANES specimen numbers were scanned by the barcode reader. The VIDAS instrument reads the specimen reactivity of each sample and assigns numeric values.
Refer to the laboratory method files section for a detailed description of the laboratory method files used.
CMV cycled back into the survey from NHANES 2011-2012 and there were no changes to the lab method, lab equipment, or lab site for this component in the NHANES 2017-2018 cycle.
Cytomegalovirus (CMV) serology (IgG, IgM, and avidity) (February 2020)
Serum specimens were processed, stored, and shipped to the National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA for analysis.
Detailed instructions on specimen collection and processing instructions are discussed in the NHANES Laboratory Procedures Manual (LPM). Vials were stored under appropriate frozen (-30oC) conditions until they were shipped to the National Center for Infectious Diseases for testing.
The NHANES quality assurance and quality control (QA/QC) protocols meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed QA/QC instructions are discussed in the NHANES LPM.
Mobile Examination Centers (MECs)
Laboratory team performance is monitored using several techniques. NCHS and contract consultants use a structured competency assessment evaluation during visits to evaluate both the quality of the laboratory work and the quality-control procedures. Each laboratory staff member is observed for equipment operation, specimen collection and preparation; testing procedures and constructive feedback are given to each staff member. Formal retraining sessions are conducted annually to ensure that required skill levels were maintained.
Analytical Laboratories
NHANES uses several methods to monitor the quality of the analyses performed by the contract laboratories. In the MEC, these methods include performing blind split samples collected during “dry run” sessions. In addition, contract laboratories randomly perform repeat testing on 2% of all specimens.
NCHS developed and distributed a QC protocol for all CDC and contract laboratories, which outlined the use of Westgard rules (Westgard, et al. 1981) when running NHANES specimens. Progress reports containing any problems encountered during shipping or receipt of specimens, summary statistics for each control pool, QC graphs, instrument calibration, reagents, and any special considerations are submitted to NCHS quarterly. The reports are reviewed for trends or shifts in the data. The laboratories are required to explain any identified areas of concern.
The data were reviewed. Incomplete data and improbable values were sent to the performing laboratory for confirmation.
Refer to the 2017-2018 Laboratory Data Overview for general information on NHANES laboratory data.
There are over 800 laboratory tests performed on NHANES participants. However, not all participants provided biospecimens or enough volume for all the tests to be performed. The specimen availability can also vary by age or other population characteristics. For example, in 2017-2018, approximately 80% of children aged 1-17 years who were examined in the MEC provided a blood specimen through phlebotomy, while 95% of examined adults age 18 and older provided a blood specimen. Analysts should evaluate the extent of missing data in the dataset related to the outcome of interest as well as any predictor variables used in the analyses to determine whether additional re-weighting for item non-response is necessary.
Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for details on the use of sample weights and analytic issues.
Demographic and Other Related Variables
The analysis of NHANES laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2017-2018 Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the sample design variables. The recommended procedure for variance estimation requires use of stratum and PSU variables (SDMVSTRA and SDMVPSU, respectively) in the demographic data file.
This laboratory data file can be linked to the other NHANES data files using the unique survey participant identifier (i.e., SEQN).
Detection Limits
Since this data is reported as qualitative data, the use of lower limit of detections (LLODs) isn’t applicable.
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 1 | positive | 168 | 168 | |
| 2 | negative | 438 | 606 | |
| 3 | indeterminate | 1 | 607 | |
| . | Missing | 324 | 931 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 1 | positive | 3 | 3 | |
| 2 | negative | 600 | 603 | |
| 3 | indeterminate | 4 | 607 | |
| . | Missing | 324 | 931 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 1 | low | 16 | 16 | |
| 2 | high | 146 | 162 | |
| 3 | indeterminate | 6 | 168 | |
| . | Missing | 763 | 931 |