Many adults demonstrate antibodies to Toxoplasma gondii, the
causative organism; consequently, subclinical infection is probably common. In the
United States, it is demonstrated that 3-70% of healthy adults are serologically
positive for T. gondii. In general, the incidence of the infection varies with the
population group and the geographical area studied. T. gondii infection affects more
than 3500 newborns in the United States each year. T. gondii seropositivity rates
among HIV-infected patients vary from 10-45%. Toxoplasmic encephalitis (TE) has been
reported in 1-5% of AIDS patients. Internationally, the seropositivity prevalence rate
is as high as 75% by the fourth decade of life, in countries such as France and El Salvador.
As many as 90% of adults in Paris are seropositive. Approximately 50% of the adult
population in Germany is infected. Women of childbearing age in much of Western Europe,
Africa, and South and Central America have seroprevalence rates of greater than 50%.