Toxoplasmosis after allogeneic haematopoietic cell transplantation: experience using a PCR-guided pre-emptive approach

Abstract

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A 10-year retrospective analysis ofToxoplasma gondiiqPCR screening in allogeneic hematopoietic stem cell transplantation recipients

“…Despite the high prevalence of anti- Toxoplasma IgG positivity (58.3% of alloHSCT recipients), toxoplasmosis was infrequent in our 10 year-long study, with 0.56% and 3.5% of our patients diagnosed with Toxoplasma disease and infection, respectively. The present prevalence of Toxoplasma reactivation (4.13%) is close to the prevalence reported in the most recent studies (3.9-4.1%) (8,17,18), whereas older studies reported higher figures, from 8.7 to 18.6% (5,7,19–21). This decrease can be ascribed to the decrease of seroprevalence of anti- Toxoplasma antibodies in the general population (22).…”

“…Asymptomatic qPCR-positive patients receiving prophylaxis (n= 9) or not (n= 2) became negative on a following sample, before any treatment change or implementation. This can be expected according to Poisson’s law in case of a parasitic load at the limit of detection of the qPCR, assuming that there are no technical false positive PCR results, and can support the choice to wait for a second positive result before starting anti- Toxoplasma treatment, as proposed by Aerts et al (17). In case of a negative control qPCR, the hypothesis would be that these patients have cleared the infection, thanks to anti- Toxoplasma immune recovery.…”

“…This decrease can be ascribed to the decrease of seroprevalence of anti- Toxoplasma antibodies in the general population (22). Other sources of differences include the seropositivity prevalence in the considered country (23), the screened population (only seropositive or all alloHSCT recipients (18)), the PCR assay used (the AF146527 DNA sequence being more sensitive than the B1 gene (24)), the number of positive PCR results considered for diagnosis (≥2 in (17), versus ≥1 in others), and the frequency of sampling (usually once weekly). The Toxoplasma reactivation decrease in European alloHSCT recipients can also be simply ascribed to a better acceptance of CTX as prophylaxis of both toxoplasmosis and pneumocystosis (20).…”

“…Moreover, the decrease of the parasitic load following treatment implementation is indicative of treatment effectiveness (25). Therefore, the qPCR screening is of utmost importance before prophylaxis is begun, or when the center policy is to avoid CTX (17).…”

“…Firstly, some patients can become spontaneously qPCR-negative. This can be expected in cases of a parasitic load at the limit of detection of the qPCR and one can wait for a second positive result before starting anti- Toxoplasma treatment, as proposed by Aerts et al (18). In the case of a negative control qPCR, the hypothesis would be that these patients have cleared the infection, thanks to anti- Toxoplasma immune recovery.…”