The exclusion of recent onset toxoplasma infection in patients with prolonged IgM response by the measurement of IgA and IgG avidity

Accurate estimation of the onset of maternal toxoplasma infection is essential to establish the risk of congenital infection. Methods based on immunoglobulin (Ig) M assays are compromised by the variable persistence of the patient's IgM response. Measurement of toxoplasma-specific IgG avidity and IgA was performed in 37 clinical cases where the IgM response was known to have persisted for 6− > 24 months. Recent onset infection could be excluded by lack of detectable IgA in 30 cases and by the presence of high avidity IgG in 36 cases. Measurement of IgA or IgG avidity [4] can be used to estimate the duration of toxoplasma infection despite the patient's unusually prolonged IgM response.