• Component Description
• Eligible Sample
• Description of Laboratory Methodology
• Data Processing and Editing
• Laboratory Quality Assurance and Monitoring
• Analytic Notes
• Codebook
  • SEQN - Respondent sequence number
  • ELISA - ELISA result interpretation
  • PHASE1 - Phase I IFA Titer IgG
  • PHASE2 - Phase II IFA Titer IgG
  • SSQFEVER - Antibody to Q fever

National Health and Nutrition Examination Survey

2003-2004 Data Documentation, Codebook, and Frequencies

Coxiella Burnetii (Q Fever) Antibodies - Serum (Surplus) (SSQFEV_C)

Data File: SSQFEV_C.xpt

First Published: February 2008

Last Revised: April 2022

Component Description

Q fever is a zoonotic disease with acute and chronic stages caused by the rickettsia-like organism Coxiella burnetii. The illness was first called “Query (Q) Fever” because its etiopathognesis was not known. Since Q fever is not notifiable in many states and many human infections are inapparent, there is not reliable way of assessing how many cases of Q fever are actually occurring in the U.S Because of this, stored sera form NHANES 2003-2004 have been tested to establish baseline Q fever seroprevalence for the U.S.

Eligible Sample

All participants aged 20+ years from of NHANES 2003-2004 who gave consent for storage and future testing of their sera.

Description of Laboratory Methodology

An enzyme-linked immunosorbent assay (ELISA) will be used to initially screen all sera specimens for IgG Phase II antibody seropositivity, a marker of acute infection. The ELISA will be performed in a 96-well flat-bottomed polystyrene microtiter plates with sonicated purified antigens (Pan-Bio, Columbia, Md.) according to the kit protocol. Any sera samples positive by ELISA will then be tested by immunofluorescence antibody assay (IFA) in order to obtain end point titers for IgG to both phase I and phase II antigens. The IFA test will be performed by the method of Philip et al. and adapted to C. burnetii (purified phases I and II, strain Nine Mile; Rocky Mountain Laboratories, Hamilton, Mont.) as described elsewhere. Serial twofold dilutions of sera will be prepared in phosphate-buffered saline containing 1% bovine serum albumin and 1% normal goat serum. After incubation at 37^oC for 30 minutes, the slides are washed with PBS and normal yolk sac and fluorescein isothiocyanate-conjugated goat anti-human IgG (gamma-chain specific) added at the optimal dilution. This is incubated and washed as before. The slides are counterstained using Eriochrome black T and coverslipped with an antifade mounting medium . The wells are examined under 400x magnification and any well with distinct fluorescence of the organisms is scored as positive.

Data Processing and Editing

Data was received after all the antibody testing was complete. The data were not edited.

Data Access: All data are publicly available.

Laboratory Quality Assurance and Monitoring

For ELISA testing, a random sample of positive samples will be retested to assure positional accuracy. Positive and negative control sera will be included in each test series.

Analytic Notes

There are four variables.

Elisa result:
1 = Positive
2 = Negative
3 = Equivocal

If the ELISA result was positive or equivocal, Phase 1 and Phase II IFA titers were performed. Titers are expressed as whole numbers (eg. 1:16 = 16, 1:32=32 etc.). Titers less than 1:16 have been re-coded to an 8 (1:8). Titers greater than 1:2048 were coded as 4096.

The final results of C. burnetii infection was determined if Phase I or Phase II IgG IFA titer was > = 1:16.
IFA Final interpretation:
1 = Positive
2 = Negative

Codebook and Frequencies