Interlaboratory comparison of polymerase chain reaction for the detection of Toxoplasma gondii DNA added to samples of amniotic fluid

To investigate the accuracy of the polymerase chain reaction (PCR) method for the detection of Toxoplasma gondii in clinical specimens, aliquots of amniotic fluid to which known amounts of Toxoplasma gondii DNA had been added were tested by five European Centres. Four laboratories were able to detect DNA at levels equivalent to ten tachyzoites or less, including two that detected DNA equivalent to a single parasite. Two laboratories erroneously found one of eight negative control samples to be positive. These findings confirm that the high level of sensitivity associated with the PCR method can be readily achieved under routine laboratory conditions, but they also underscore the potential for both false-positive and false-negative findings to occur. Furthermore, the results confirm the urgent need for an external quality assurance scheme to support laboratories employing PCR in a clinical context for the detection of Toxoplasma gondii.