Any measurement in which the number of individuals in a study population that display an infection with the parasite Toxoplasma gondii at a point in time or develop an infection with the parasite Toxoplasma gondii within a determined period of time are compared to the total number of individuals in the study population. Often expressed as a percentage but could be expressed as a ratio. Toxoplasma gondii is a sporozoan species that is an intracellular parasite in a variety of vertebrates and is the causative agent of toxoplasmosis.