LOW INCIDENCE OF PRIMARY INFECTION WITH TOXOPLASMA AMONG WOMEN IN SHEFFIELD - A SEROCONVERSION STUDY

Objective To determine the incidence of primary toxoplasma infection i n women of childbearing age. Design A retrospective study of seroconve rsion on stored pairs of sera taken for routine antenatal testing. Set ting The antenatal clinics and general practices of Sheffield between July 1989 and October 1992. Subjects One thousand six hundred and twen ty-one women on whom pairs of sera, separated by more than 500 days, h ad been received. Main outcome measure Rate of primary infection deter mined by seroconversion as measured by the presence of antibody in the second serum and its absence in the first. Results Of 1621 women, 160 (9.9%) were initially seropositive. One seroconversion was detected i n 2966 woman years of observation for susceptibles. The projected rate for primary infections was 0.23 (95% CI 0.0059-1.3) per 1000 pregnanc ies. Conclusions The rate is much lower than for earlier estimates of incidence in the UK but agrees with a more recent estimate from Sheffi eld and suggests a falling incidence.