MODELING AGE-SPECIFIC AND TIME-SPECIFIC INCIDENCE FROM SEROPREVALENCE- TOXOPLASMOSIS

New forms of catalytic epidemic models were developed to estimate the incidence of primary toxoplasmosis infection from age- and time-specif ic seroprevalence data collected from persons aged 0-100 years in Sout h Yorkshire, England, 1969-1990. Piecewise constant and exponential po lynomial functions were used to assess the way in which incidence depe nded on age and time, and to guide the choice of parametric models sui table for prediction. Incidence estimates were biased unless both age- and time-dependence were allowed for. New findings on the epidemiolog y of this infection emerged. Incidence appears to have fallen sixfold between 1915 and 1970, but has remained stable for the last 20 years. There is a marked peak in incidence in childhood. The incidence throug hout the childbearing period is currently estimated to be 0.07 or less per 100 susceptible persons per year. However, these predictions were highly sensitive to assumptions about incidence in childhood, and the 95% confidence limits for a range of models were between 0.003 and 0. 32% per year. Age- and time-specific seroprevalence data can be collec ted inexpensively on a mass population basis, and, with appropriate in cidence modeling, may prove to be a powerful method for the study of i nfectious disease and for incidence prediction.