This study has a serious confounding limitation — accidentally swallowing T. gondii through contact with cat feces that contain Toxoplasma. This might happen by 1. cleaning a cat’s litter box when the cat has shed Toxoplasma in its feces, 2. touching or ingesting anything that has come into contact with cat feces that contain Toxoplasma, 3. accidentally ingesting contaminated soil (e.g., not washing hands after gardening or eating unwashed fruits or vegetables from a garden). click here for more.
Does NHANES have a metadata field for “Cat present/not present in the home?”. If not, then I’d say cat-associated exposures are more likely than well water to be the cause of endemic levels of Toxoplasma.
Krueger WS, Hilborn ED, Converse RR, Wade TJ. BMC Public Health. 2014 Jul 10;14(1):711. Drinking water source and human Toxoplasma gondii infection in the United States: a cross-sectional analysis of NHANES data.
BACKGROUND: Toxoplasma gondii imparts a considerable burden to public health. Human toxoplasmosis can be life-threatening in immunocompromised individuals, has been associated with psychiatric disorders, and can cause severe congenital pathologies, spontaneous abortion, or stillbirth. Environmental modes of transmission contributing to the incidence of human toxoplasmosis are poorly understood. We sought to examine National Health and Nutrition Examination Survey (NHANES) data for risk factors associated with T. gondii seroprevalence.
METHODS: T. gondii serology results reported for Continuous NHANES survey years 1999-2004 and 2009-10 were examined. To explore associations with toxoplasmosis seropositivity, covariates of interest were selected a priori, including source and home treatment of tap water. Associations between potential risk factors and evidence of IgG antibodies against T. gondii were assessed using multivariable logistic regression.
RESULTS: Among 23,030 participants with available T. gondii serology across 8 years of continuous NHANES survey data (1999-2004; 2009-2010), persons born outside the United States were significantly more likely to be seropositive, and seropositivity was inversely associated with years spent in the United States. Among US-born participants, participants with homes on well water (both those who used at-home water treatment devices and those who did not), as well as participants with public/private company-provided tap water who did not use at-home water treatment devices, were significantly more likely to be seropositive compared to participants who used home treatment devices on tap water provided by a private or public water company. A comparative subpopulation analysis revealed age-adjusted seroprevalence among US-born persons 12-49 yrs old significantly declined to 6.6% (95% CI, 5.2-8.0) (P < 0.0001) in 2009-10, compared to previously published reports for NHANES data from 1988-1994 (14.1%) and 1999-2004 (9.0%).
CONCLUSIONS: Data suggests that T. gondii infections continue to decline in the United States, but the overall infection rate remains substantial at nearly 7%. Despite the limitations in the Continuous NHANES cross-sectional survey, the association between well water use and T. gondii infection warrants further research.
Click here for full paper (Open Source).