Early detection of Toxoplasma infection by molecular monitoring of Toxoplasma gondii in peripheral blood samples after allogeneic stem cell transplantation.

Background: Isolated case reports have shown that recipients of allogeneic hematopoietic stem cell transplants (HSCTs) who develop toxoplasmosis may have circulating Toxoplasma gondii DNA in peripheral blood before the onset of clinical symptoms.

Methods: We prospectively studied 106 T. gondii-seropositive adult recipients of HSCTs for the incidence of reactivation of toxoplasmosis in the first 6 months after transplantation. Toxoplasmosis infection (TI) was defined by a positive result of polymerase chain reaction (PCR) of peripheral blood specimens, whereas toxoplasmosis disease (TD) was defined as an invasive infection.

Results: The incidence of TI was 16% (95% confidence interval [CI], 8%-21%), whereas the incidence of TD was 6% (95% CI, 1%-10%). In the 16 patients with TI, the incidence of disease was 38%, whereas it was 0% in patients without TI (P<.0001). In most patients, the onset of TD or treatment for TI was preceded by an increase in the parasite load in peripheral blood samples, as determined by quantitative PCR.

Conclusions: Toxoplasmosis occurs more commonly after HSCT than has previously been suggested, and routine PCR testing of peripheral blood specimens may be an appropriate tool for guiding preemptive therapy in patients at very high risk of developing invasive disease.