An investigation into the incidence of toxoplasmosis in pregnancy in New Zealand

Aim. To estimate the incidence of toxoplasmosis in pregnancy in New Zealand and consider whether there is a case for screening women in pregnancy, Methods. The risk of maternal and fetal infection with toxoplasmosis was de rived by first determining the rate of maternal seroconversion based on ser oprevalence studies. The age-specific number of seroconversions in pregnanc y was then estimated from the birth rate. Using reported fetal infection ra tes after primary maternal infection, the expected number of congenitally i nfected infants in one year was estimated. These incidences were compared w ith the number of recognised cases of toxoplasmosis infection in pregnancy and the actual number of positive IgM results at the Wellington Hospital la boratory, Using national births data, this incidence was extrapolated to es timate the number of expected cases in New Zealand; Results, The annual seroconversion rate was 0.62% (95% confidence interval 0.39-0.86). On this basis, 164 primary maternal infections are expected ann ually with 66 fetuses being infected. Ten patients tested positive for IgM in Wellington, which averaged only one case per year being identified over the time examined in this study. Conclusions. Very few of the expected cases in pregnancy are diagnosed. Rep orting rates were low when toxoplasmosis was a notifiable disease. Other me ans of improving detection, reporting and the avoidance of infection are di scussed. More information is required before screening can be recommended i n New Zealand.