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Toxoplasma seroprevalence in a rural population in France: detection of a household effect.

Fromont EG, Riche B, Rabilloud M - BMC Infect. Dis. (2009)

Bottom Line: These effects were close to statistical significance.The major finding is the household effect, with a strong heterogeneity of seroprevalence among households.This effect may be explained by common exposures of household members to local risk factors.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratoire de Biométrie et Biologie Evolutive, Equipe Ecologie Evolutive des Populations, UMR5558, CNRS, Villeurbanne, France. fromont@biomserv.univ-lyon1.fr

ABSTRACT

Background: Toxoplasma gondii, the agent of toxoplasmosis, has a complex life cycle. In humans, the parasite may be acquired either through ingestion of contaminated meat or through oocysts present in the environment. The importance of each source of contamination varies locally according to the environment characteristics and to differences concerning human eating habits and the presence of cats; thus, the risk factors may be determined through fine-scale studies. Here, we searched for factors associated with seropositivity in the population of two adjacent villages in Lorraine region, France.

Methods: All voluntary inhabitants filled out a questionnaire and gave a blood sample. The seroprevalence was estimated globally and according to the inhabitants' ages using a cubic spline regression. A mixed logistic regression model was used to quantify the effect of individual and household factors on the probability of seropositivity.

Results: Based on serological results from 273 persons, we estimated seroprevalence to be 47% (95% confidence interval: 41 to 53%). That seroprevalence increased with age: the slope was the steepest up to the age of 40 years (OR = 2.48 per 10-year increment, 95% credibility interval: [1.29 to 5.09]), but that increase was not significant afterwards. The probability of seropositivity tended to be higher in men than in women (OR = 2.01, 95% credibility interval: [0.92 to 4.72]) and in subjects eating raw vegetables at least once a week than in the others (OR = 8.4, 95% credibility interval: [0.93 to 72.1]). These effects were close to statistical significance. The multivariable analysis highlighted a significant seroprevalence heterogeneity among households. That seroprevalence varied between 6 and 91% (5th and 95th percentile of the household seropositivity distribution).

Conclusion: The major finding is the household effect, with a strong heterogeneity of seroprevalence among households. This effect may be explained by common exposures of household members to local risk factors. Future work will quantify the link between the presence of oocysts in the soil and the seroprevalence of exposed households using a spatial analysis.

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Age-specific observed seroprevalence with 95% confidence intervals, in 7 age classes (<20, [20–30], [30–40], [40–50], [50–60], [60–70], and 70 years and over) and estimated probability of seropositivity depending on age (line).
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Figure 1: Age-specific observed seroprevalence with 95% confidence intervals, in 7 age classes (<20, [20–30], [30–40], [40–50], [50–60], [60–70], and 70 years and over) and estimated probability of seropositivity depending on age (line).

Mentions: The estimate of overall Toxoplasma seroprevalence was 47% (128/273, 95% CI: 41 – 53%). The functional form of the change of seroprevalence over age showed a strong increase between 7 and 40 years but a weaker increase after the age of 40 years (Figure 1). The estimated seroprevalence increased from about 2.5% at 7 years to about 50% at 40 years. At 95 years old, the estimated seroprevalence was about 75%.


Toxoplasma seroprevalence in a rural population in France: detection of a household effect.

Fromont EG, Riche B, Rabilloud M - BMC Infect. Dis. (2009)

Age-specific observed seroprevalence with 95% confidence intervals, in 7 age classes (<20, [20–30], [30–40], [40–50], [50–60], [60–70], and 70 years and over) and estimated probability of seropositivity depending on age (line).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2696459&req=5

Figure 1: Age-specific observed seroprevalence with 95% confidence intervals, in 7 age classes (<20, [20–30], [30–40], [40–50], [50–60], [60–70], and 70 years and over) and estimated probability of seropositivity depending on age (line).
Mentions: The estimate of overall Toxoplasma seroprevalence was 47% (128/273, 95% CI: 41 – 53%). The functional form of the change of seroprevalence over age showed a strong increase between 7 and 40 years but a weaker increase after the age of 40 years (Figure 1). The estimated seroprevalence increased from about 2.5% at 7 years to about 50% at 40 years. At 95 years old, the estimated seroprevalence was about 75%.

Bottom Line: These effects were close to statistical significance.The major finding is the household effect, with a strong heterogeneity of seroprevalence among households.This effect may be explained by common exposures of household members to local risk factors.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratoire de Biométrie et Biologie Evolutive, Equipe Ecologie Evolutive des Populations, UMR5558, CNRS, Villeurbanne, France. fromont@biomserv.univ-lyon1.fr

ABSTRACT

Background: Toxoplasma gondii, the agent of toxoplasmosis, has a complex life cycle. In humans, the parasite may be acquired either through ingestion of contaminated meat or through oocysts present in the environment. The importance of each source of contamination varies locally according to the environment characteristics and to differences concerning human eating habits and the presence of cats; thus, the risk factors may be determined through fine-scale studies. Here, we searched for factors associated with seropositivity in the population of two adjacent villages in Lorraine region, France.

Methods: All voluntary inhabitants filled out a questionnaire and gave a blood sample. The seroprevalence was estimated globally and according to the inhabitants' ages using a cubic spline regression. A mixed logistic regression model was used to quantify the effect of individual and household factors on the probability of seropositivity.

Results: Based on serological results from 273 persons, we estimated seroprevalence to be 47% (95% confidence interval: 41 to 53%). That seroprevalence increased with age: the slope was the steepest up to the age of 40 years (OR = 2.48 per 10-year increment, 95% credibility interval: [1.29 to 5.09]), but that increase was not significant afterwards. The probability of seropositivity tended to be higher in men than in women (OR = 2.01, 95% credibility interval: [0.92 to 4.72]) and in subjects eating raw vegetables at least once a week than in the others (OR = 8.4, 95% credibility interval: [0.93 to 72.1]). These effects were close to statistical significance. The multivariable analysis highlighted a significant seroprevalence heterogeneity among households. That seroprevalence varied between 6 and 91% (5th and 95th percentile of the household seropositivity distribution).

Conclusion: The major finding is the household effect, with a strong heterogeneity of seroprevalence among households. This effect may be explained by common exposures of household members to local risk factors. Future work will quantify the link between the presence of oocysts in the soil and the seroprevalence of exposed households using a spatial analysis.

Show MeSH
Related in: MedlinePlus