Quality control for the diagnosis of Toxoplasma gondii reactivation in SCT patients using PCR assays

Guidelines for the management of Toxoplasma gondii infection and disease in patients with haematological malignancies and after haematopoietic stem-cell transplantation: guidelines from the 9th European Conference on Infections in Leukaemia, 2022

Patients with haematological malignancies might develop life-threatening toxoplasmosis, especially after allogeneic haematopoietic stem-cell transplantation (HSCT). Reactivation of latent cysts is the primary mechanism of toxoplasmosis following HSCT; hence, patients at high risk are those who were seropositive before transplantation. The lack of trimethoprim-sulfamethoxazole prophylaxis and various immune status parameters of the patient are other associated risk factors. The mortality of toxoplasma disease-eg, with organ involvement-can be particularly high in this setting. We have developed guidelines for managing toxoplasmosis in haematology patients, through a literature review and consultation with experts. In allogeneic HSCT recipients seropositive for Toxoplasma gondii before transplant, because T gondii infection mostly precedes toxoplasma disease, we propose weekly blood screening by use of quantitative PCR (qPCR) to identify infection early as a pre-emptive strategy. As trimethoprim-sulfamethoxazole prophylaxis might fail, prophylaxis and qPCR screening should be combined. However, PCR in blood can be negative even in toxoplasma disease. The duration of prophylaxis should be a least 6 months and extended during treatment-induced immunosuppression or severe CD4 lymphopenia. If a positive qPCR test occurs, treatment with trimethoprim-sulfamethoxazole, pyrimethamine-sulfadiazine, or pyrimethamine-clindamycin should be started, and a new sample taken. If the second qPCR test is negative, clinical judgement is recommended to either continue or stop therapy and restart prophylaxis. Therapy must be continued until a minimum of two negative PCRs for infection, or for at least 6 weeks for disease. The pre-emptive approach is not indicated in seronegative HSCT recipients, after autologous transplantation, or in non-transplant haematology patients, but PCR should be performed with a high level of clinical suspicion.

Infectious diseases in allogeneic haematopoietic stem cell transplantation: prevention and prophylaxis strategy guidelines 2016

Infectious complications after allogeneic haematopoietic stem cell transplantation (allo-HCT) remain a clinical challenge. This is a guideline provided by the AGIHO (Infectious Diseases Working Group) of the DGHO (German Society for Hematology and Medical Oncology). A core group of experts prepared a preliminary guideline, which was discussed, reviewed, and approved by the entire working group. The guideline provides clinical recommendations for the preventive management including prophylactic treatment of viral, bacterial, parasitic, and fungal diseases. The guideline focuses on antimicrobial agents but includes recommendations on the use of vaccinations. This is the updated version of the AGHIO guideline in the field of allogeneic haematopoietic stem cell transplantation utilizing methods according to evidence-based medicine criteria.

Toxoplasma prophylaxis in haematopoietic cell transplant recipients: a review of the literature and recommendations

PURPOSE OF REVIEW

Toxoplasmosis in haematopoietic cell transplant (HCT) recipients is associated with high morbidity and mortality rates. Prophylaxis following HCT is recommended for high-risk pre-HCT toxoplasma-seropositive (pre-HCTSP) recipients. However, there is no agreement or consistency among programmes on whether to adopt prophylaxis or not, or if used, on the chosen antitoxoplasma prophylactic regimen. This review discusses the role of prophylaxis, and preemptive treatment, for toxoplasmosis in the setting of HCT.

RECENT FINDINGS

Approximately two-thirds of toxoplasmosis cases following HCT are reported in allogeneic pre-HCTSP (allo pre-HCTSP) patients. This finding confirms a major role of reactivation of latent infection in the pathogenesis of toxoplasmosis in this patient population. Toxoplasma disease-related mortality in allo pre-HCTSP patients was reported at 62%, but it can be significantly decreased with early detection and treatment of toxoplasma infection. There are no randomized trials comparing the efficacy of different prophylactic agents to prevent toxoplasmosis after HCT. Several observational studies have demonstrated the efficacy of trimethoprim-sulfamethoxazole (TMP/SMX) in decreasing the incidence of toxoplasmosis following HCT. There is limited information regarding efficacy of other prophylactic agents. Preemptive treatment using routine blood PCR monitoring seems to be beneficial in detecting infection early and preventing disease in several observational studies and has been adopted for allo pre-HCTSP HCT patients when universal prophylaxis is not possible.

SUMMARY

Universal prophylaxis with TMP/SMX in allo pre-HCTSP patients should be implemented by all transplant programmes. Preemptive treatment with routine blood PCR monitoring is an option if prophylaxis cannot be used.

Determining Toxoplasma high-risk autologous and allogeneic hematopoietic stem cell transplantation patients by systematic pre-transplant PCR screening of stem cell originated buffy coat

The diagnosis of Toxoplasma infection or disease in hematopoietic stem cell transplantation (HSCT) patients is achieved mainly by PCR screening; however screening did not find wide field of use in practice due to costly expenditures of PCR. This study aimed to determine patients at high risk of Toxoplasma infection or disease before transplantation by stem cell originated buffy coat PCR and subsequently to screen them. Buffy coats collected from 12 autologous and 18 allogeneic HSCT patients' donors were investigated by PCR before transplantation. After transplantation, blood and sera collected at fixed time intervals were screened by two PCR methods and serological assays. Screening results first time assessed a toxoplasmosis incidence level as 25% in autologous HSCT patients and increased incidence level in allogeneic HSCT patients to 22%. Importantly, buffy coat PCR was first time performed before transplantation, to determine the risk of toxoplasmosis. Buffy coat PCR results showed that four patients were at high risk of toxoplasmosis before transplantation. After transplantation, these patients experienced toxoplasmosis. In conclusion, for the determination of patients at risk of toxoplasmosis, clinicians should consider buffy coat PCR in combination with serology before transplantation. After transplantation, PCR screening can be initiated in high risk patients upon clinical suspicion.

Multicentric comparative analytical performance study for molecular detection of low amounts of Toxoplasma gondii from simulated specimens

Although screening for maternal toxoplasmic seroconversion during pregnancy is based on immunodiagnostic assays, the diagnosis of clinically relevant toxoplasmosis greatly relies upon molecular methods. A problem is that this molecular diagnosis is subject to variation of performances, mainly due to a large diversity of PCR methods and primers and the lack of standardization. The present multicentric prospective study, involving eight laboratories proficient in the molecular prenatal diagnosis of toxoplasmosis, was a first step toward the harmonization of this diagnosis among university hospitals in France. Its aim was to compare the analytical performances of different PCR protocols used for Toxoplasma detection. Each center extracted the same concentrated Toxoplasma gondii suspension and tested serial dilutions of the DNA using its own assays. Differences in analytical sensitivities were observed between assays, particularly at low parasite concentrations (<or=2 T. gondii genomes per reaction tube), with "performance scores" differing by a 20-fold factor among laboratories. Our data stress the fact that differences do exist in the performances of molecular assays in spite of expertise in the matter; we propose that laboratories work toward a detection threshold defined for a best sensitivity of this diagnosis. Moreover, on the one hand, intralaboratory comparisons confirmed previous studies showing that rep529 is a more adequate DNA target for this diagnosis than the widely used B1 gene. But, on the other hand, interlaboratory comparisons showed differences that appear independent of the target, primers, or technology and that hence rely essentially on proficiency and care in the optimization of PCR conditions.

Incidence and diagnosis of active toxoplasma infection among liver transplant recipients in Western Turkey

Toxoplasmosis is a serious and potentially life-threatening disease in liver transplant recipients while they are immunosuppressed. We report the clinical and laboratory findings related to active toxoplasma infection associated with 40 immunosuppressed liver transplant procedures that took place over a 12-month period at a major transplant unit in Izmir, Turkey. Twenty-seven (67.5%) of the 40 transplant recipients were found to be seropositive for toxoplasma infection and therefore at risk of reactivated infection. From the serological status of the donors, which was ascertained in 38 of 40 cases, we identified 3 (7.9%) of 38 transplants to be from a seropositive donor to a seronegative recipient. In 10 (26.3%) of 38 transplants, both the donor and recipient were seronegative, and this excluded toxoplasma as a risk. A comparison of real-time polymerase chain reaction (PCR) and nested PCR was undertaken in combination with a range of serological assays (the Sabin-Feldman dye test, enzyme immunoassay immunoglobulin M, and immunosorbent agglutination assay immunoglobulin M). Ethylene diamine tetraacetic acid blood samples from 3 of the 30 recipients at risk from toxoplasma were found positive by PCR, but only 1 of these was found positive in both assays. Among the 3 PCR-positive patients, immunoglobulin M and immunoglobulin G antibody levels increased in only 1 patient. Correlations between symptoms, laboratory findings, and clinical management (use of anti-toxoplasma therapy) are presented. Our findings suggest that toxoplasma presents a significant risk to our liver transplant population and that PCR is a helpful addition in identifying active infections and hence in informing clinical management decisions.

Three years of multi-laboratory external quality control for the molecular detection of Toxoplasma gondii in amniotic fluid in France

Between 2002 and 2004, panels of amniotic fluid containing varying concentrations of Toxoplasma gondii were sent to up to 23 laboratories in France for molecular (PCR-based) detection as part of a national quality assurance initiative in the molecular prenatal diagnosis of toxoplasmosis. Participants were free to enroll and no fees were required. The general level of sensitivity was high, and the rate of false-positive reactions was relatively low. Considerable diversity among PCR methods and primers was revealed. This external quality assurance scheme provided the opportunity to improve laboratory practice and performance, and to increase communication among laboratories involved in making this diagnosis.

[Real-time PCR in the diagnosis of toxoplasmosis: the way to standardisation?]

Severity of toxoplasmosis is highly correlated to the immune status of the infected individual. Foetus and immunocompromised patient are mostly at risk to develop life threatening forms. In this situation, serological diagnosis gives poor information. DNA detection using polymerase-chain-reaction technology (PCR) has significantly improved the management of this disease. Even so, the growing number of conventional PCR assays has finally led to variable performance results. Real-Time PCR (RT-PCR) in toxoplasmosis has been developed since 2000. This new technology can improve standardisation. Moreover, quantification of parasitic load in samples becomes possible. This review describes the main RT-PCR procedures actually under use and the studies comparing different target genes. The effective benefit of quantification is also discussed. Reducing number of procedures and more systematic external quality control should be considered, in order to improve reliability in PCR results, which has undoubtedly become a major tool in toxoplasmosis diagnosis.

Multicenter proficiency study for detection of Toxoplasma gondii in amniotic fluid by nucleic acid amplification methods

A proficiency panel was designed to assess the performance of nucleic acid amplification technologies for the detection of Toxoplasma gondii in amniotic fluid.

METHODS

The proficiency panel consisted of five lyophilised coded samples in a range of concentration between 5 to 1000 parasites/ml and a negative control. The distribution also included a questionnaire on the applied methods.

RESULTS

Thirty-three laboratories in 17 countries participated and returned a total of 38 data sets. The percentage of data sets achieving correct results on all panel samples was 42.1%, whereas two or more incorrect or equivocal results were reported for 36.8%. The lowest concentration (5 parasites/ml) was not identified correctly in 15 (39.5%) data sets. False positive results were reported by two laboratories both of which had not included a step in their procedure to rule out contamination. In 32 (84.2%) data sets an "in-house" method was used, and in 6 (15.8%) sets a commercial assay was applied.

CONCLUSIONS

Overall, the results of this study demonstrate the need for improvements in both sensitivity and specificity of molecular detection methods of T. gondii and for the development of international reference materials to help laboratories with the development and validation of their assays.

Comparison between two amplification sets for molecular diagnosis of toxoplasmosis by real-time PCR

PCR is now commonly applied to the diagnosis of toxoplasmosis. Although several methods are available, comparative studies are few, making it difficult to compare the performance of each technique. We compared the sensitivities of two real-time PCR assays through a prospective study on fetuses, neonates, and immunocompromised patients and on the ocular diagnosis of toxoplasmosis. The first system targeted the widely used B1 gene (GenBank accession number AF179871) while the second (RE) targeted a more recently described sequence repeated roughly 200 to 300 times (GenBank accession number AF146527). We demonstrated that molecular diagnosis requires the duplication of PCR assays, especially with the B1 system, as only one PCR was positive in 33.3% of cases. Our study showed that the RE target was more sensitive for all biological samples (amniotic fluid, placenta, aqueous humor, whole blood, and cerebrospinal and bronchoalveolar fluids) and significantly improved the performance of the diagnosis of toxoplasmosis. Taking into consideration all clinical samples, the mean gain in the crossing point value was 4.2 +/- 1.7 cycles and was even more significant for amniotic fluid (5.8 +/- 1.7 cycles).

Towards a nucleic acid-based diagnosis in clinical parasitology and mycology

BACKGROUND

Multiple in-house polymerase chain reaction (PCR) assays for the diagnosis of parasitic and fungal diseases have been reported. Encouraging results have been published to anticipate or improve the diagnosis. However, the absence of standardized methods has led to discrepant results. As a consequence, these tests are not recognized as consensual diagnostic criteria.

METHODS

The major breakthrough for improving the results of these methods is the emergence of real-time technologies. This markedly improves the reliability of the PCR results by dramatically decreasing the risk of false positive results due to PCR products carryover. Moreover, the quantitative results provided by these techniques allow to compare rapidly the efficiency of primers, probes, and DNA extraction. Therefore, one can expect a more consensual method to implement comparisons between laboratories. Automated DNA extraction should also be useful to achieve this goal. Whatever sophisticated technology is used, the meaning of detecting nucleic acids in a given clinical sample still needs to be defined. This requires well-designed studies with clinical consensual criteria and PCR techniques that are as similar as possible.

CONCLUSIONS

The development of real-time technology should improve our knowledge in order to give the clinicians informative clues for decision-making.

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.

Comparison of two widely used PCR primer systems for detection of toxoplasma in amniotic fluid, blood, and tissues

The PCR diagnosis of toxoplasmosis suffers from lack of standardization. Interlaboratory comparative studies of PCR methods have been performed, but intralaboratory comparisons are scarce. Here, we optimized and compared the technical performances of two PCR primer systems widely used for Toxoplasma detection. The differences between the two methods were visible only at low parasite concentrations (< or = 1 Toxoplasma genome per reaction tube). Nevertheless, when clinical samples were tested, both methods significantly differed in their technical sensitivities and specificities. Only one method appeared adequate for samples containing blood or tissue.

Molecular diagnostics in clinical parasitology and mycology: limits of the current polymerase chain reaction (PCR) assays and interest of the real-time PCR assays

Polymerase chain reaction (PCR) represents a major breakthrough for the diagnosis of infectious diseases. However, the absence of standardized kits for commercially unattractive targets, such as most of the parasites and the fungi, has led to the development of numerous in-house PCR assays. The performances reported, both for the sensitivity and the specificity of these assays are very divergent. For instance, for the antenatal diagnosis of toxoplasmosis, the sensitivity is either 97.4%, or 64%. For the diagnosis of toxoplasmosis in HIV-positive patients, the PCR on blood is either of limited value with a sensitivity of 13% or of excellent yield with a sensitivity of 87.5%. Similar results are reported for the diagnosis of invasive aspergillosis in bone-marrow-transplant recipients. The patients and the clinical specimens tested are often different. This can explain some of the discrepancies. However, when performed, the quality controls on identical specimens show different results depending on the laboratories. An analysis of the PCR techniques used shows that the control of false positive results as a result of carry-over and false negative results owing to PCR inhibitors is far from being systematic. These shortcomings of 'classical' PCR should be solved when real-time PCR assays are developed, leading to some standardization. Automated DNA extraction should also be useful to achieve this goal. Comparison between laboratories should then be possible and regular quality controls will be necessary to ensure the reliability of real-time PCR assays.

Toxoplasma gondii: transmission, diagnosis and prevention

Toxoplasmosis, caused by the protozoan parasite Toxoplasma gondii, is one of the most common parasitic infections of man and other warm-blooded animals. It has been found world-wide from Alaska to Australia. Nearly one-third of humanity has been exposed to this parasite. In most adults it does not cause serious illness, but it can cause blindness and mental retardation in congenitally infected children and devastating disease in immunocompromised individuals.