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 [greater than or equal to] 10 IU. This cutoff change from >6 to [greater than or equal 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).

After this correction, the overall age-adjusted 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).

Jeffrey L. Jones, * Deanna Kruszon-Moran, ([dagger]) and Marianna Wilson *

* Centers for Disease Control and Prevention, Atlanta, Georgia, USA; and ([dagger]) Centers for Disease Control and Prevention, Hyattsville, Maryland, USA

References

(1.) Jones JL, Kruszon-Moran DK, Wilson M. Toxoplasma gondii infection in the United States, 1999-2000. Emerg Infect Dis. 2003;9:1371-4.

(2.) 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.

Address for correspondence: Jeffrey L. Jones, Centers for Disease Control and Prevention, Mailstop F22, 4770 Buford Highway, Atlanta, GA 30341, USA; email: [e-mail]

Table. Comparison of Toxoplasma gondii IgG antibody seroprevalence,
NHANES 1999-2000 and NHANES III (1988-1994) * ([dagger])

                                         NHANES 1999-2000

                        N ([double dagger])    Prevalence    95% CI

Total                          4,234              14.3       12.3-16.2
Sex
  Male                         2,013              15.2       12.4-18.0
  Female                       2,221              13.4       11.2-15.5
Race/ethnicity
  Non-Hispanic white           1,293              10.8        8.1-13.6
  Non-Hispanic black           1,027              16.8       13.4-20.3
  Mexican American             1,553              14.2       10.1-18.4
Age group, y
  12-19                        2,105               7.3        4.7-10.0
  20-29                         735               11.9        9.5-14.4
  30-39                         726               17.0       12.9-21.2
  40-49                         668               18.7       15.0-22.3
Country of birth
  United States                3,211              10.5       8.3-12.8
  Not United States             995               32.0       24.0-39.9

                                       NHANES III (1988-1994)

                        N ([double dagger])    Prevalence    95% CI

Total                         11,132              16.0       14.5-17.5
Sex
  Male                         5,144              16.7       14.8-18.6
  Female                       5,988              15.3       13.5-17.0
Race/ethnicity
  Non-Hispanic white           3,304              14.3       12.5-16.2
  Non-Hispanic black           3,674              18.0       16.1-19.8
  Mexican American             3,661              18.3       16.7-20.0
Age group, y
  12-19                        2,749               8.5        6.4-10.5
  20-29                        3,100              15.2       12.1-18.3
  30-39                        2,960              16.1       14.6-17.6
  40-49                        2,323              22.2       19.4-25.0
Country of birth
  United States                8,606              14.1       12.7-15.5
  Not United States            2,493              27.9       24.1-31.7

* IgG, immunoglobulin G; NHANES, National Health and Nutrition
Examination Survey; CI, confidence interval.

([dagger]) Sex, race/ethnicity, country of birth,and total values are
age-adjusted to the 2000 census-estimated population using the 4 age
categories shown.

([double dagger]) Totals for the race/ethnicity and country-of-birth
categories do not add up to the total number because an "other"
race/ethnicity category was included in the totals but not shown in
these categories or because persons did not provide a response to
country-of-birth questions.