Volume 13, Number 4—April 2007
Toxoplasma gondii Prevalence, United States
To the Editor: We correct the prevalence of Toxoplasma gondii immunoglobulin (Ig) G antibodies published in Emerging Infectious Diseases in 2003 (1). An incorrect cutoff value in the computer program used to calculate seropositivity of anti–T. gondii IgG antibody resulted in some incorrect prevalence rates. We discovered this error when analyzing more recent National Health and Nutrition Examination Survey (NHANES) data.
The cutoff value for anti–T. gondii IgG seropositivity used in the prior publication (1) was >6 IU, which is the correct value for NHANES III 1988–1994 data (2) but not for NHANES 1999–2000 data. Because of a change by the T. gondii test kit manufacturer, the cutoff value for NHANES 1999–2000 seropositivity data was increased to ≥10 IU. This cutoff change from >6 to ≥10 IU does not cause a large difference in the T. gondii seroprevalence reported. In addition, it does not change the overall findings of the article or the overall relationship between NHANES III (1988–1994) and NHANES 1999–2000. However, it does produce a borderline change for 2 demographic subgroups (non-Hispanic white persons and persons born in the United States), for whom the difference from NHANES III to NHANES 1999–2000 data reached statistical significance at p<0.05 in the t test, but the 95% confidence intervals (CIs) for the prevalence estimates for these groups still overlapped between NHANES III and NHANES 1999–2000 (i.e., the t test is a less conservative measure of association than CI).[[AA:T1:PREVIEWHTML]]
After this correction, the overall T. gondii antibody prevalence according to NHANES 1999–2000 data changed from 15.8% (95% CI 13.5%–18.1%) to 14.3% (95% CI 12.3%–16.2%). The Table shows the overall and stratified seroprevalence rates for NHANES 1999–2000 (corrected) compared with NHANES III (no corrections needed).
- Jones JL, Kruszon-Moran DK, Wilson M. Toxoplasma gondii infection in the United States, 1999–2000. Emerg Infect Dis. 2003;9:1371–4.
- Jones JL, Kruszon-Moran DK, Wilson M, McQuillan G, Navin T, McAuley JB. Toxoplasma gondii infection in the United States: seroprevalence and risk factors. Am J Epidemiol. 2001;154:357–65.