Attitude towards positive Toxoplasma quantitative PCR results in allogeneic hematopoietic stem cell transplantation recipients: a 10-year retrospective analysis.

Weekly blood Toxoplasma gondii DNA screening using real-time quantitative polymerase chain reaction (qPCR) has been implemented in all allogeneic hematopoietic stem cell transplantation (alloHSCT) recipients at our hospital. We retrospectively analyzed the consequences of a positive blood qPCR in the management of Toxoplasma infection (TI) and disease (TD). From 2011 to 2020, 52 (4.13%) of 1 257 alloHSCT recipients had at least one positive qPCR, 45 (3.5%) with TI and seven (0.56%) with TD (central nervous system involvement). Forty-four patients were qPCR-positive before day 100, 30 without and 14 with anti-Toxoplasma prophylaxis. Twenty-five of them (56.8%) started or continued prophylactic dosage treatment: all became qPCR-negative, including 20 (80%) receiving only prophylactic dosage treatment. Twenty-four of them (54.5%) received non-prophylactic dosage treatment: qPCR became negative in 22/24 (91.7%), while TI contributed to death in two cases. Six of the eight patients diagnosed after D100 were breakthrough TI or TD. No death was attributable to TI or TD. qPCR kinetics available for 24 patients increased until anti-Toxoplasma treatment began, then decreased with all treatment regimens. Clinical follow-up and qPCR monitoring with quantification of the parasitic load appears a reasonable strategy to avoid TD and to use minimal effective dosage of anti-Toxoplasma treatments.