SARS-CoV-2 specific antibody response after an mRNA vaccine as the third dose: homologous versus heterologous boost

Implementacija treće doze vakcine protiv SARS-CoV-2 u preporuke širom sveta otvorila je polje istraživanja heterologog pristupa revakcinaciji, odnosno kombinacije primarne serije vakcine i treće doze različite vakcinalne platforme. Iako je literatura bogata radovima na temu heterologog pristupa, imunogenost i trajanje humoralnog imunskog odgovora nakon kombinacije inaktivisane BBIBPCorV i iRNK vakcine nisu dovoljno istraženi. Stoga, cilj ove studije bio je ispitivanje razlike u imunogenosti i dugotrajnosti humoralnog imunskog odgovora u okviru perioda od šest meseci nakon treće doze kod homologog (tri doze BNT162b2) i heterologog (BBIBP-CorV/BNT162b2) pristupa revakcinaciji tokom Omikron talasa u Srbiji. U studiju je uključen 91 ispitanik, od kojih se 55 odlučilo za homologi a 36 za heterologi pristup. Serumi ispitanika analizirani su u četiri vremenske tačke: šest meseci nakon prve doze, a zatim tri nedelje, tri meseca i šest meseci nakon treće doze. IgG antitela specifična za receptor-vezujući domen “šiljastog” (eng. spike) proteina detektovana su BioMerieux VIDAS SARS-CoV-2 IgG testom. Tri nedelje nakon treće doze, oba pristupa revakcinaciji dovela su do značajnog porasta u koncentraciji antitela (p<0.0001). Štaviše, ispitanici koji su se opredelili za heterologu kombinaciju imali su statistički značajno više koncentracije antitela od homologe grupe, u kontrolnim vremenskim tačkama na tri nedelje i tri meseca nakon treće doze (p=0.025, p=0.0006). Međutim, značajan pad humoralnog imunskog odgovora zapažen je tokom vremena kod oba pristupa. Većina infekcija nakon vakcinacije registrovana je u periodu između tri i šest meseci nakon treće doze (n=22), a ukupna incidencija ovih infekcija za posmatrani period iznosila je 36.36% (20/55) nakon homologog i 16.67% (6/36) nakon heterologog pristupa. Međutim, ispitanici sa potvrđenom infekcijom nakon vakcinacije nisu imali pneumoniju niti su bili hospitalizovani. Iako je heterologi pristup indukovao više koncentracije antitela, naši rezultati ukazuju da su i heterologi i homologi pristup indukovali potentan humoralni imunski odgovor i odgovarajuću zaštitu od hospitalizacije i smrtnog ishoda tokom Omikron talasa. Međutim, opadanje imunskog odgovora opaženo kod oba vakcinalna pristupa u periodu od šest meseci, kao i konstantna opasnost od pojave novih pretećih varijanti, ukazuje na potrebu preispitivanja trenutne vakcinalne strategije.Worldwide implementation of the third dose of vaccine against SARS-CoV-2 opened a new field of research concerning the heterologous boost i.e., the combination of the primary vaccine series and a different vaccinal platform for the third dose. Although literature is replete with studies of heterologous boosts, longevity and immunogenicity of the inactivated BBIBP-CorV and mRNA BNT162b2 combination remains under-explored. Thus, the aim of this study was to evaluate the differences in immunogenicity and longevity of the humoral immune response within six months after the third dose in both homologous (BNT162b2) and heterologous (BBIBP-CorV/BNT162b2) vaccination setting, and to assess the real-life data in the middle of the Omicron surge in Serbia. A total of 91 individuals were included in this study, of which 55 received homologous and 36 heterologous boost. Serum samples were analyzed at four timepoints: six months after the first dose; three weeks, three months, and six months after the third dose. Specific IgG antibodies against the receptor-binding domain of the spike protein were detected using BioMerieux VIDAS SARS-CoV-2 IgG kit. Both groups showed a highly significant increase in antibody concentrations (p<0.0001) three weeks after the boost. Furthermore, comparison per timepoint has shown that recipients of heterologous boost had significantly higher antibody concentrations than homologous group, at three weeks and three months after the boost (p=0.025, p=0.0006). However, a significant decline in antibody response over time was noted for both strategies. The majority of breakthrough infections were registered in the period between three and six months after the boost (n=22).Furthermore, total incidence was estimated at 36.36% (20/55) for homologous group, and 16.67% (6/36) for heterologous group. Most importantly, none of the recipients of the third dose developed pneumonia during the breakthrough infection, and none were hospitalized. In conclusion, although heterologous approach resulted in higher antibody concentrations, our findings imply that both homologous and heterologous boost induce potent humoral immune response and adequate protection against hospitalization and death in the Omicron setting. However, waning immune response registered for both types of boosts within six months and constant threats of new emerging variants, calls for an update of vaccine strategy

Three Outbreaks of COVID-19 in a Single Nursing Home over Two Years of the SARS-CoV-2 Pandemic

Older people in nursing homes (NH) have been hit particularly hard by the COVID-19 pandemic. We conducted a retrospective study of three outbreaks of COVID-19, occurring during the waves of the initial pre-Alpha, Delta and Omicron SARS-CoV-2 variants, in one NH in suburban Belgrade, Serbia. All staff and 95% residents were vaccinated in February 2021, mostly with BBIBP-CorV, and two thirds were boosted with a third dose in August 2021. COVID-19 was diagnosed by positive PCR and/or antigen test. After the first outbreak, 80 affected individuals were tested for SARS-CoV-2 specific antibodies. The first outbreak involved 64/126 (50.8%) residents and 45/64 (70.3%) staff, the second 22/75 (29.3%) residents and 3/40 (7.5%) staff, and the third involved 36/110 (32.7%) residents and 19/56 (33.9%) staff. Clinical presentation ranged from asymptomatic to severe, with severe cases referred to hospital ICUs. Deaths occurred only in residents, and the case fatality rate was 31.2%, 9.1% and 0%, respectively in outbreaks 1, 2 and 3. Specific IgG antibodies were detected in all 35 residents and 44 of the 45 staff, and higher IgG levels were detected in the residents (417.3±273.5) than in the staff (201.9±192.9, p<0.0001) despite a double difference in age (79.0±7.4 vs. 40.1±11.5 years). Outbreaks 2 and 3 involved four and 23 breakthrough infections, respectively. Older individuals mounted a good immunological response to SARS-CoV-2 infection and vaccination, which prevented significant mortality and severe morbidity in the subsequent outbreaks, despite a significant number of breakthrough infections

Prospective Cohort Study of the Kinetics of Specific Antibodies to SARS-CoV-2 Infection and to Four SARS-CoV-2 Vaccines Available in Serbia, and Vaccine Effectiveness: A 3-Month Interim Report

Real-life data on the performance of vaccines against SARS-CoV-2 are still limited. We here present the rates of detection and levels of antibodies specific for the SARS-CoV-2 spike protein RBD (receptor binding domain) elicited by four vaccines available in Serbia, including BNT-162b2 (BioNTech/Pfizer), BBIBP-CorV (Sinopharm), Gam-COVID-Vac (Gamaleya Research Institute) and ChAdOx1-S (AstraZeneca), compared with those after documented COVID-19, at 6 weeks and 3 months post first vaccine dose or post-infection. Six weeks post first vaccine dose, specific IgG antibodies were detected in 100% of individuals fully vaccinated with BNT-162b2 (n = 100) and Gam-COVID-Vac (n = 12) and in 81.7% of BBIBP-CorV recipients (n = 148), while one dose of ChAdOx1-S (n = 24) induced specific antibodies in 75%. Antibody levels elicited by BNT-162b2 were higher, while those elicited by BBIBP-CorV were lower, than after SARS-CoV-2 infection. By 3 months post-vaccination, antibody levels decreased but remained ≥20-fold above the cut-off in BNT-162b2 but not in BBIBP-CorV recipients, when an additional 30% were seronegative. For all vaccines, antibody levels were higher in individuals with past COVID-19 than in naïve individuals. A total of twelve new infections occurred within the first 3 months post-vaccination, eight after the first dose of BNT-162b2 and ChAdOx1-S (one each) and BBIBP-CorV (six), and four after full vaccination with BBIBP-CorV, but none required hospitalization

Postnatal ocular toxoplasmosis in immunocompetent patients

Introduction: Ocular toxoplasmosis is the most common cause of infectious posterior uveitis worldwide. It can be prenatal or postnatal in origin. Despite estimations that postnatal ocular toxoplasmosis is more prevalent, only several cases of proven postnatal ocular toxoplasmosis have been reported in non-epidemic settings. Here, the clinical evolution of ocular toxoplasmosis of conclusively proven postnatal origin in immunocompetent patients is reported.Methodology: Postnatal ocular toxoplasmosis was diagnosed based on clinical diagnosis supported by the longitudinal detection of Toxoplasma gondii-specific IgG, IgM and IgA antibodies in the serum as well as by direct detection of the parasite (bioassay) and/or its DNA (real-time PCR) in aqueous humor.Results: Three cases involved adults in whom ocular toxoplasmosis developed during primary T. gondii infection, as part of the clinical presentation in two and as the sole manifestation in one patient. The fourth patient was a case of inactive ocular toxoplasmosis in a 14-year-old boy, where postnatal infection was confirmed by exclusion of maternal infection. The causative parasite strain was genotyped in only one case and it belonged to genotype II, the dominant type in Europe. One patient acquired the infection in Africa, suggesting an atypical strain.Conclusions: The distinction between prenatal and postnatal ocular toxoplasmosis is only possible in particular clinical situations, and requires extensive laboratory investigation. Genotyping of the parasite strain involved may be important, particularly if atypical strains are suspected, requiring tailored treatment approaches

Three Episodes of COVID-19 in a Nursing Home in Belgrade, Serbia

Background: Over the two years of the COVID-19 pandemic, the elderly in nursing homes (NH) have been hit particularly hard. Methods: We conducted a retrospective study of 3 episodes of COVID-19 in one NH in suburban Belgrade, Serbia, at the time of pre-alpha (Nov 2020), delta (Nov 2021) and omicron (Jan 2022) variants of SARS-CoV-2. All staff and 95% of residents were vaccinated in the early spring of 2021, with BBIBP-CorV, Gam-COVID-Vac and BNT162b2 vaccines. COVID-19 was diagnosed by positive PCR and/or antigen test. Specific IgG antibodies against SARS-CoV-2 S glycoprotein RBD were assessed by ELISA. Results: The 3 episodes involved a total of 188 infections. The first involved 65/126 (51.9%) residents and 44/64 (68.7%) staff, the second 22/75 (29.3%) residents and 3/40 (7.5%) staff, and the third 36/110 (32.7%) residents and 18/56 (32.1%) staff. Clinical presentation ranged from asymptomatic to severe, with severe cases being referred to hospital ICUs. Mortality per episode was 19.8%, 2.7% and 0%, respectively, and involved residents only. After the first episode, all 36 examined residents and 43 of the 44 staff had specific antibodies. Interestingly, higher levels (20.45±13.27) were detected in the residents than in the staff (9.74±9.52) (p<0.001) despite a double difference in age (79.6±7.48 vs. 40.8±11.43) (p<0.001). Episodes 2 and 3 involved 4 (1 resident, 3 staff) and 22 (13 residents, 9 staff) breakthrough infections. Conclusions: Elderly individuals mounted a good immunological response to the vaccines, which prevented significant mortality in the next episodes, despite a significant number of omicron-induced breakthrough infections

Toxoplasma gondii Genotypes Circulating in Serbia—Insight into the Population Structure and Diversity of the Species in Southeastern Europe, a Region of Intercontinental Strain Exchange

In Europe, Toxoplasma gondii lineage II is dominant, and ToxoDB#1 the most frequently occurring genotype. The abundance of lineage III genotypes varies geographically and lineage I are rare, yet present in several regions of the continent. Data on the T. gondii population structure in southeastern Europe (SEE) are scarce, yet necessary to appreciate the diversity of the species in Europe. To help fill this gap, we genotyped 67 strains from nine species of intermediate hosts in Serbia by MnPCR-RFLP, determined the population structure, and identified the genotypes using ToxoDB. A neighbor-joining tree was also constructed from the isolates genotyped on nine loci. While 42% of the total genotype population consisted of ToxoDB#1 and ToxoDB#2, variant genotypes of both lineages comprised 46% of the population in wildlife and 28% in domestic animals and humans. One genotype of Africa 4 lineage was detected in a human sample. Interestingly, the findings include one lineage III variant and one II/III recombinant isolate with intercontinental distribution, which appear to be moderately related to South American genotypes. Based on these findings, SEE is a region of underappreciated T. gondii genetic diversity and possible strain exchange between Europe and Africa

Eksperimentalna terapija malarije – novi vidici

With an estimated 247 million cases annually and 619.000 deaths (in 2021) malaria remains a major disease of the developing world and globally the most important parasitic disease. Because of widespread resistance to available antimalarials including chloroquine (CQ) and its derivatives, new drugs are urgently needed. Here we report on the antimalarial efficacy of new 4-aminoquinoline derivatives, with modifications at the linker and at the quinoline nucleus. In vitro screening was performed by the lactate dehydrogenase assay, based on measurement of the plasmodial lactate dehydrogenase activity in both a CQ-sensitive (3D7) and a CQ-resistant (Dd2) strain of Plasmodium falciparum, with a CQ as a control. In vivo antimalarial activity was investigated in C57BL/6 mice infected with Plasmodium berghei ANKA strain by the modified Thompson test. Compounds were first tested for toxicity. A total of 37 compounds were screened in vitro. Of the 22 that passed the first screening, 18 had IC50 values lower than CQ in the Dd2 strain while only one was efficient in the 3D7 strain. However, even 15 compounds showed in vivo activity, significantly (P<0.05) prolonging survival of treated vs. untreated mice. Among these, seven compounds afforded the survival of 20–100% of treated mice up to Day 31, with or without the detection of parasites in peripheral blood. Most importantly, three of these, including ClAQ1, FClAQ1 and ClAQ8, afforded survival of 100% of animals, the first two at 80 and 160 mg/kg/day and the last only at 160 mg/kg/day.Survival was associated with complete parasite clearance, as shown by both microscopy and qPCR. Of note, continuous monitoring of parasitemia allowed the observation of a potentially important phenomenon, that a number of compounds were able to confer resistance to cerebral malaria and afford a switch to hyperparasitaemia to mice prone to the neurological syndrome. By comparing the antimalarial activity of this group of novel compounds, we found that even minor structural modifications substantially affect activity. The results of this extensive study are important, as they may guide future work involving structural modifications of aminoquinolines, and as a contribution to the knowledge in the field of malarial chemotherapy.Malarija ostaje globalno najznačajnija parazitska infekcija sa procenjenih 247 miliona slučajeva i 619.000 smrtnih slučajeva godišnje (2021.). Zbog široko rasprostranjene rezistencije na dostupne antimalarike, uključujući hlorokvin (CQ) i njegove derivate, hitno su potrebni novi lekovi. U ovom istraživanju ispitana je potencijalna antimalarijska aktivnost 37 novosintetisanih aminohinolina sa hemijskim modifikacijama na aminohinolinskom jezgru i bočnom lancu. In vitro skrining aktivnosti jedinjenja vršen je kolorimetrijskim esejom laktat dehidrogenaze na dva soja Plasmodium falciparum, osetljivim (3D7) i rezistentnim (Dd2) na CQ, uz CQ kao pozitivnu kontrolu. Aktivnost u in vivo sistemu je ispitana na ženkama miševa soja C57Bl/6 inficiranim ANKA sojem Plasmodium berghei primenom modifikovanog Thompson-ovog testa. Ispitivanju aktivnosti jedinjenja prethodila je faza kliničkog praćenja zdravih životinja terapiranih eksperimentalnim jedinjenjima. Od 37 jedinjenja ispitanih u fazi in vitro skrininga, 22 koja su inhibirala ≥50% rast bar jednog od dva soja P. falciparum odabrana su za titraciju do IC50 vrednosti. Prema soju rezistentnom na CQ, 18 jedinjenja se pokazalo aktivnijim od CQ, dok je među njima samo jedno jedinjenje bilo aktivnije i prema osetljivom soju. Čak 15 jedinjenja ispitanih u in vivo sistemu značajno je produžilo život inficiranim životinjama u odnosu na kontrolnu grupu (P < 0.05). Među njima, sedam jedinjenja je omogućilo preživljavanje 20–100% tretiranih miševa do dana 31, sa ili bez nalaza parazita u perifernoj krvi. Posebno treba istaći tri jedinjenja koja su dovela do izlečenja svih tretiranih životinja, ClAQ1 i FClAQ1 (80 i 160 mg/kg/dan) i ClAQ8 (160 mg/kg/dan).Preživljavanje je bilo praćeno i kompletnim klirensom parazita što je dokazano mikroskopskim pregledom razmaza kao i qPCR analizom krvi i tkiva jetre preživelih životinja. Važno je pomenuti da je kontinuirano praćenje parazitemije svih tretiranih miševa omogućilo da se zapazi potencijalno značajan fenomen. Naime, neka jedinjenja su omogućila da miševi postanu otporni na razvoj cerebralne malarije i uzrokovala da miševi skloni razvoju neurološkog sindroma tolerišu preživljavanje sa izuzetno velikim brojem parazita. Poređenjem antimalarijske aktivnosti novosintetisanih aminohinolina uočeno je da i male strukturne promene u velikoj meri menjaju aktivnost. Rezultati ovog opsežnog istraživanja su od značaja za buduća istraživanja strukturne modifikacije aminohinolina i doprinose proširenju znanja u oblasti hemioterapije malarije

Computational image analysis reveals the structural complexity ofToxoplasma gondiitissue cysts

Toxoplasma gondiiis an obligate intracellular parasite infecting up to one third of the human population. The central event in the pathogenesis of toxoplasmosis is the conversion of tachyzoites into encysted bradyzoites. A novel approach to analyze the structure ofin vivo-derived tissue cysts may be the increasingly used computational image analysis. The objective of this study was to quantify the geometrical complexity ofT.gondiicysts by morphological, particle, and fractal analysis, as well as to determine if it is impacted by parasite strain, cyst age, and host type. A total of 31 images ofT.gondiibrain cysts of four type-2 strains (Me49, and local isolates BGD1, BGD14, and BGD26) was analyzed using ImageJ software. The parameters of interest included diameter, circularity, packing density (PD), fractal dimension (FD), and lacunarity. Although cyst diameter varied widely, its negative correlation with PD was observed. Circularity was remarkably close to 1, indicating a perfectly round shape of the cysts. PD and FD did not vary among cysts of different strains, age, and derived from mice of different genetic background. Conversely, lacunarity, which is a measure of heterogeneity, was significantly lower for BGD1 strain vs. all other strains, and higher for Me49 vs. BGD14 and BGD26, but did not differ among Me49 cysts of different age, or those derived from genetically different mice. The results indicate a highly uniform structure and occupancy of the differentT.gondiitissue cysts. This study furthers the use of image analysis in describing the structural complexity ofT.gondiicyst morphology, and presents the first application of fractal analysis for this purpose. The presented results show that use of a freely available software is a cost-effective approach to advance automated image scoring forT.gondiicysts

Structural Characterization of Toxoplasma gondii Brain Cysts in a Model of Reactivated Toxoplasmosis Using Computational Image Analysis

Toxoplasma gondii is an obligate intracellular parasite existing in three infectious life stages—tachyzoites, bradyzoites, and sporozoites. Rupture of tissue cysts and re-conversion of bradyzoites to tachyzoites leads to reactivated toxoplasmosis (RT) in an immunocompromised host. The aim of this study was to apply ImageJ software for analysis of T. gondii brain cysts obtained from a newly established in vivo model of RT. Mice chronically infected with T. gondii (BGD1 and BGD26 strains) were treated with cyclophosphamide and hydrocortisone (experimental group—EG) or left untreated as infection controls (ICs). RT in mice was confirmed by qPCR (PCR+); mice remaining chronically infected were PCR−. A total of 90 images of cysts were analyzed for fractal dimension (FD), lacunarity (L), diameter (D), circularity (C), and packing density (PD). Circularity was significantly higher in PCR+ compared to IC mice (p < 0.05 for BGD1, p < 0.001 for the BGD26 strain). A significant negative correlation between D and PD was observed only in IC for the BGD1 strain (ρ = −0.384, p = 0.048), while fractal parameters were stable. Significantly higher D, C, and PD and lower lacunarity, L, were noticed in the BGD1 compared to the more aggressive BGD26 strain. In conclusion, these results demonstrate the complexity of structural alterations of T. gondii cysts in an immunocompromised host and emphasize the application potential of ImageJ in the experimental models of toxoplasmosis

Transplantation-related risk of Toxoplasma gondii infection: the National Reference Laboratory prospective cohort study results

Toksoplazmoza je česta ali kod pacijenata lečenih transplantacijom uglavnom zanemarena i pogrešno dijagnostikovana oportunistička infekcija koja može ugroziti engraftment ali može i evoluirati u životno ugrožavajuću diseminovanu infekciju. Nakon transplantacije, infekcija parazitom Toxoplasma gondii se može razviti kao reaktivacija hronične infekcije ili može biti preneta graftom. Naša osmogodišnja prospektivna studija bila je usmerena na dijagnostiku i monitoring toksoplazmatske infekcije (TI) kod primalaca matičnih ćelija hematopoeze (haematopoietic stem cell transplant, HSCT) u centru koji primenjuje protokol uzdržavanja od profilakse do engraftmenta, i kod primalaca transplantata srca (heart transplant, HT) koji su na kontinuiranoj profilaksi trimetoprim- sulfametoksazolom (TMP-SMX). Cilj nam je bio utvrđivanje incidence TI u ova dva vrlo različita transplantaciona režima, i to pre nego što evoluira u klinički manifestnu, potencijalno fatalnu bolest (Toxoplasma disease, TD). Pre-transplantacioni serološki i qPCR skrining u post-transplantacionom toku zamenjen je redovnim qPCR monitoringom iz uzoraka periferne krvi (peripheral blood, PB) usmerenim na Toxoplasma 529 bp gen. Kod primalaca HSCT, qPCR je rađen jednom nedeljno dok je kod primalaca HT qPCR rađen jednom mesečno prva dva meseca post-HT i potom jednom godišnje. TI je dijagnostikovana na bazi pozitivnog PCR rezultata iz bar jednog uzorka PB. TI je dijagnostikovana kod 21/104 (20.2%) primalaca HSCT, prevashodno nakon alogene (19/75) i retko nakon autologne HSCT (2/29). Više od 50% slučajeva TI dijagnostikovano je tokom prvog meseca post-HSCT, pre engraftmenta odnosno tokom uzdržavanja od profilakse. Sa druge strane, TI je dijagnostikovana kod 3/37 (8.1%) primalaca HT. Uprkos primeni TMP-SMX, qPCR je postao pozitivan godinu dana posle HT kod dva i dve godine post-HSCT kod trećeg pacijenta. Infekcija je bila preneta graftom kod 2/3 (seronegativni) a reaktivirana kod 1/3 primalaca HT (seropozitivni primalac HT poreklom od seropozitivnog donora). Naši rezultati potvrđuju da je sistemski qPCR monitoring iz uzoraka PB dragocen u dijagnostici TI ne samo kod primalaca HSCT već i kod primalaca solidnih organa, posebno nakon HT. Učestalost qPCR monitoringa se mora adaptirati shodno specifičnostima transplantacionog protokola, pre svega primeni profilakse ali i osnovnoj dijagnozi, na način koji omogućava pravovremenu primenu specifične terapije u svakom slučaju TI.Toxoplasmosis is a common but often neglected and misdiagnosed opportunistic infection in transplant recipients, which can not only compromise the engraftment, but also evolve into life-threatening disseminated infection. Post-transplantation, Toxoplasma gondii infection can develop as a reactivation of chronic infection or could be graft-transmitted. We conducted an eight-year-long prospective study on the diagnosis and monitoring of Toxoplasma infection (TI) in haematopoietic stem cell transplant (HSCT) recipients in a setting that withholds prophylaxis until engraftment, and in heart transplant (HT) recipients on continuous trimethoprim-sulfamethoxazole (TMP-SMX) prophylaxis. The objective was to determine the incidence of TI before it evolves into clinical, potentially fatal Toxoplasma disease (TD), in these two very different transplantation settings. Pre-transplantation serological and qPCR screening was followed by post-transplantation peripheral blood (PB)-based qPCR monitoring targeting the Toxoplasma 529 bp gene. In HSCT recipients, qPCR was performed weekly while in HT recipients, qPCR was performed monthly for two months post-HT and then yearly. TI was diagnosed based on a positive PCR result in at least one PB sample. TI was diagnosed in 21/104 (20.2%) HSCT recipients, predominantly after allogeneic (19/75) and rarely after autologous HSCT (2/29). Over 50% of TI cases were diagnosed during the first month post-HSCT, while awaiting engraftment without prophylaxis. On the other hand, TI was diagnosed in 3/37 (8.1%) HT recipients. Regardless of the TMP-SMX prophylaxis, qPCR became positive one year after HT in two and two years post-HSCT in third patient. Infection was graft-transmitted in 2/3 (seronegative) and reactivated in 1/3 OHT (seropositive recipient of a seropositive donor’s heart transplant). The presented results show that systematic PB-based qPCR monitoring is a valuable resource for the diagnosis of TI not only in HSCT but also in solid organ recipients, especially after HT. Frequency of qPCR monitoring should be adjusted according to the specificity of the transplantation setting, especially in terms of prophylaxis but also an underlying diagnosis, in a manner allowing for prompt introduction of specific treatment in each case of TI