Toxoplasma gondii, Brazil.

To the Editor

Recently, Jones et al. reported that past pregnancies increased risk for recent Toxoplasma gondii infection in Brazil (). They did not, however, control for age. Previous seroepidemiologic studies have shown that age is a main confounding variable in analysis of risk factors for toxoplasmosis (). Age can explain why mothers with more children are at higher risk for toxoplasmosis; the longer persons live in areas with high toxoplasmosis prevalence, the higher their risk for infection.

Also not explored were drinking water–related factors. Our recent study of pregnant women in Quindio, Colombia, found factors that explained attributable risk percent for infection to be eating rare meat (0.26%) and having contact with a cat <6 months of age (0.19%) (). Drinking bottled water was more significantly protective for the group that did not consume undercooked or raw meat (odds ratio 0.06, 95% confidence interval 0.006–0.560, p = 0.008). We think that drinking water–related factors could explain up to 50% of toxoplasmosis infections in our region.

We thank Dr Gomez-Marin for his letter regarding our article on recently acquired Toxoplasma gondii infection in Brazil (). Dr Gomez-Marin states that perhaps age could account for our finding that having had children was a risk factor for recent T. gondii infection among women. Studies have shown that age is a risk factor for prevalent T. gondii infection; i.e., infection prevalence increases with age (). However, age is not necessarily a risk factor for recent (incident) infection.

Our study of risk factors for T. gondii infection was a case-control design to evaluate recent infection, not a cross-sectional study of T. gondii infection prevalence in a population. In our study, case-patients with recent infection were similar in age to T. gondii–negative control-patients, although among women the mean age of case-patients (33 years) differed slightly from that of control-patients (29 years) (p = 0.03, t-test). In addition, multivariate analysis comparing the case-patients with control-patients showed that age was not a significant factor. However, when we kept age in the multivariate model for women (p = 0.87 for age in the model), the odds ratio for having had children changed little, from 14.94 (95% confidence interval [CI] 3.68–60.73) to 14.01 (95% CI 2.88–68.08). Therefore, we do think that, in this study population, having had children is a risk factor for T. gondii infection among women.

Dr Gomez-Marin also states that we did not evaluate drinking water–related factors. However, in our methods section (), we indicated that our questionnaire asked about a comprehensive set of risk factors related to drinking water. Specifically, the questionnaire asked about the types of water (city, private well, and others, including bottled water); chlorination; filtering of water; and ingestion of water from streams, lakes, rivers, ponds, or other sources. Although we evaluated numerous water-related factors, we did not find them to be significant in this study, which applies to 1 area of Brazil. In other areas of Brazil, however, studies in which 1 of our authors (J.L.J.) has been involved have found water to be a risk factor or a source of infection (,).