In individuals on effective antiretroviral therapy (ART), integrated HIV proviruses persist within CD4 T cells, forming a viral reservoir that rebounds if treatment is stopped. Identifying and targeting these rare, infected cells is critical for advancing therapies, but methods to study reservoir cells are limited, and their unique properties remain largely unknown. We applied DAb-seq, a high-throughput method that combines single-cell DNA and surface protein sequencing, to profile ~527,000 CD4 T cells from the blood of six individuals on ART. Infected cells were distributed across all CD4 T cell subsets but were enriched in central memory subsets and in a CD4 subset with Th17-like signatures expressing high levels of integrin β7. Attempts to identify surface markers distinguishing infected from uninfected cells revealed epitopes that largely reflected the subsets most enriched for infection. However, while central memory T cells harbored the majority of HIV, proviruses with a greater number of genomic regions were enriched relative to their more defective counterparts in the CD4 Naïve, transitional memory (Ttm), and regulatory (Treg) subsets, suggesting that these subsets differentially maintain more complete proviral genomes. In summary, we developed DAb-seq as an open-source platform to link proviral sequences to cellular phenotypes, revealing heterogeneity in surface protein expression and proviral fate across infected subsets.

Broadly neutralizing antibodies (bNAbs) have been associated with enhancement of HIV-specific T or B cell responses and sustained partial control of HIV replication in some people with HIV (PWH). The mechanisms through which bNAbs may potentiate host immunity in this context are not known. We previously reported the outcomes of a clinical trial in which ten PWH on antiretroviral therapy (ART) received a combination of immunotherapies including two bNAbs administered immediately preceding an analytic treatment interruption (ATI). After bNAb levels waned, seven participants exhibited varying degrees of post-intervention control of HIV linked to a robust expansion of activated CD8+ T cells in response to rebounding virus. To investigate the role of the bNAbs in enhancing endogenous immune responses, we looked for evidence of HIV-specific or broader immune activation during the period after ART was paused and prior to rebound when bNAbs were controlling HIV replication. At a timepoint early post-ART interruption and at least one month before virus emerged in plasma, we detected an increase in levels of plasma inflammatory proteins as well as phenotypic and transcriptional activation of innate and adaptive immune cells. Compared to non-controllers, post-intervention controllers demonstrated unique transcriptional activation patterns as well as differential longitudinal plasma inflammatory protein trends. No enhancement of HIV-specific T cell or antibody responses was observed in this window. This study identifies activated cell types and inflammatory pathways that are recruited early during bNAb-mediated HIV suppression and that may play a role in potentiating long-lasting HIV immune control after bNAb therapy.

As the most abundant human cell and the foundation of transfusion medicine, red blood cells (RBCs) offer a unique readout of systemic health, yet they have never been characterized at population scale. We generated a proteome atlas of 13,091 blood donors with multi-omics longitudinal phenotyping, characterizing the influence of demographics and genetic variation on the reproducibility of RBC proteomes across donations. Elastic-net aging clocks captured biological aging with high accuracy and uncovered genetic regulators of ΔAge at FN1, C4/IKZF1, CRAT, PFAS, TRIM58. Across independent cohorts, ΔAge was accelerated in G6PD deficiency, sickle cell trait/disease, and iron deficiency, reversed by iron repletion, and slowed in high-frequency donors, linking molecular aging to brain iron/myelin and cognitive performance. Molecular aging signatures predicted storage, osmotic, and oxidative hemolysis, hemoglobin increments after transfusion, and long-term donor activity over 12-years. These results establish RBC proteomics as a scalable biomarker of aging, donor healthspan, and transfusion outcomes. Abstract Figure: Highlights:RBC proteome atlas of 13,091 donors reveals demographic and genetic programsGenetically encoded RBC aging clocks identify regulators of molecular ΔageMolecular aging features predict hemolysis and transfusion response across cohortsRBC molecular age forecasts long-term donor activity over a 12-year follow-up.

BACKGROUND:Transfusion-transmitted malaria remains a concern in non-endemic regions due to asymptomatic parasitemia in donors with prior residence in or travel to malaria-endemic areas. Nucleic acid testing (NAT)-based screening has been proposed to mitigate this risk, and supplemental assays are needed to confirm reactive donations. We developed a pan-Plasmodium reverse transcription quantitative PCR (RT-qPCR) assay with species identification capability as a supplemental tool for malaria donor screening. STUDY DESIGN AND METHODS:The assay targets a conserved region of the 18S rRNA shared by all five human-infecting Plasmodium species and is compatible with whole blood lysed using Grifols' parasite transport medium (PTM). Analytical performance was evaluated using in vitro transcripts and infected red blood cells (iRBCs), with the limit of detection (LoD) determined by probit analysis. Specificity was assessed against Babesia microti and 300 non-exposed US donor samples. Clinical sensitivity was evaluated using infected specimens; species identification was performed by sequencing of RT-qPCR amplicons. RESULTS:The assay demonstrated high amplification efficiency (97.2%) and linearity (R2 = 0.99). The 95% LoD was 5.3 iRBCs/mL (95% CI: 3.2-8.6), comparable to the Procleix Plasmodium Assay. Clinical sensitivity was 100% across all five Plasmodium species, and clinical specificity was 100% (95% CI: 99-100%), with no cross-reactivity with Babesia. Amplicon sequencing enabled accurate species-level identification of all sequenced specimens. DISCUSSION:This assay provides a sensitive confirmatory tool for malaria NAT-based donor screening. Its compatibility with PTM lysates and species identification capabilities supports regulatory applications and research into asymptomatic parasitemia in semi-immune donors.

Chronic red blood cell (RBC) transfusion sustains patients with diverse hematologic disorders, but repeated transfusion leads to iron overload and alloimmunization. Reducing transfusion burden requires identifying donor units that circulate more effectively after storage, yet determinants of this variability remain incompletely defined. Here, we integrate forward genetics in mice, multi-omics analyses of over 13,000 human donors, and studies of two families with hereditary ATP11c mutations to reveal a central role for this phospholipid flippase in transfusion efficacy. We show that common ATP11C variants, including the missense SNP V972M, and rare familial loss-of-function alleles impair RBC survival by disrupting membrane lipid remodeling and cytoskeletal stability—a mechanism distinct from oxidative damage pathways. Together, these findings establish ATP11c as a novel determinant of transfusion outcomes across species and genetic contexts, and highlight opportunities for donor stratification and improved storage technologies to advance precision transfusion medicine.

Abstract To understand the impact of blood donor and product characteristics on platelet transfusion outcomes, we linked these variables with recipients of single-unit apheresis-derived platelet products between 1 June 2020 and 31 March 2022. We used multivariable logistic regression to examine associations between donor and product characteristics on posttransfusion platelet counts and 24-hour red blood cell (RBC) transfusion events in 2808 transfusion recipients who received ≥1 platelet transfusions (N = 8207 units). Posttransfusion platelet increments >20 × 109/L and RBC transfusion within 24 hours occurred after 24.9% and 37.7% of platelet transfusion events, respectively. After multivariable adjustment, donor variables, including increasing body mass index (BMI), platelet unit concentration, and elevated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid antibody levels, were associated with increased odds of recipient platelet increments of >20 × 109/L; whereas pathogen reduction, storage in platelet additive solution (PAS), platelet splits, and platelet storage between 5 and 7 days were associated with reduced odds. In parallel, increasing donor BMI and elevated SARS-CoV-2 nucleocapsid antibody levels were associated with lower odds of 24-hour RBC transfusion events. In contrast, pathogen reduction and irradiation were associated with increased odds of RBC transfusion, whereas longer storage, storage in PAS, and platelet unit concentration and splits were not associated with changes in RBC transfusion events. In conclusion, blood donor and product characteristics are predictors of changes in platelet counts and RBC requirements after platelet transfusion. Future studies examining the impact of blood donor and product characteristics on platelet function could be used to optimize platelet transfusion practice.

Introduction This study investigated whether HIV binding antibody (Ab) and p24 antigen (Ag) quantitation could detect humoral immune responses or p24 Ag before or following detectable plasma viral load (VL) rebound during antiretroviral therapy interruption (ATI) and provide insights into post-rebound viral replication. Methods Longitudinal plasma samples collected before and following ATI from 40 participants (485 samples; mean of 12/participant) in the ACTG A5345 study who began antiretroviral therapy during either acute or chronic stages of infection were analyzed using commercial immunoassays to assess HIV Ab and Ag dynamics, including following dissociation of immune complexes for improved Ag detection. Results Neither Ab nor Ag levels increased in plasma before VL rebound. However, 75% of participants exhibited increased Ab reactivity concurrent with or shortly after VL rebound, which declined upon ART reinitiation. Participants who were ART-treated early had lower Ab levels at ATI initiation but demonstrated greater fold increases in Ab during ATI than late-treated participants. Two participants who demonstrated post-treatment control of VL showed gradual Ab increases that paralleled intermittent VL elevations. p24 Ag was only detectable after dissociating immune complexes in samples with VL > 10⁴ RNA copies/mL, correlating strongly with VL levels. Conclusions Although antibody levels did not predict viral rebound, tracking their longitudinal changes provided meaningful information about viral replication patterns and immune reactivation during and after rebound, offering a practical tool for monitoring ATI outcomes.

BACKGROUND:Oropouche virus (OROV) re-emerged in Brazil in 2023, causing over 26 000 confirmed cases through December 2025. A reassortant lineage was linked to neurologic complications and congenital infections due to vertical transmission. Although transfusion transmission has not been reported, asymptomatic viremia in blood donors could represent an unrecognized route of infection. METHODS:We conducted nucleic acid testing (NAT), genomic, and serological surveillance among blood donors in Manaus, Brazil, during the 2023-2024 OROV outbreak. Minipools (MPs) of 18 donations from November 2023 to May 2024 were tested using a validated RT-qPCR assay. A subset of NAT-reactive pools underwent whole genome sequencing and phylogenetic analysis. Serosurveys in November 2023 and June 2024 assessed changes in population immunity. The RNA-detectable window was estimated by integrating NAT yield with seroincidence. RESULTS:Among 661 MPs, representing 11 898 donations, 43 (6.5%) were OROV RNA-reactive, peaking in January 2024. About half contained viral RNA concentrations above the limit of quantification. Donor-derived viral genomes clustered with the reassortant lineage circulating in Brazil. Donor seropositivity increased from 13.0% to 29.7%, corresponding to approximately 390 000 estimated infections in Manaus, substantially higher than reported case numbers. The estimated MP RNA-detectable window was 5.4 days (95% CI: 3.8-7.0). CONCLUSIONS:OROV RNA detection in donor samples, together with high-titer viremia, phylogenetic identity to the outbreak strain, and postoutbreak seroconversion, raises questions about blood safety. Continued donor and recipient surveillance will be vital to determine transfusion-transmission risk and inform transfusion safety policies.

Protein-l-isoaspartate O-methyltransferase (PIMT), encoded by PCMT1, is a repair enzyme that corrects isoaspartyl lesions, preserving protein structure and function. While indispensable for neuronal integrity, its role in red blood cells (RBCs) and transfusion outcomes is incompletely understood. Here, we show that novel erythroid-specific Pcmt1 knockout mice display profound remodeling of one-carbon metabolism, accumulation of repair intermediates, and destabilization of glycolytic and cytoskeletal proteins, yet maintain lower lipid peroxidation and normal post-transfusion recovery. Analysis of 13,091 blood donors from the Recipient Epidemiology and Donor Evaluation Study (REDS)-III Red Blood Cell Omics (RBC Omics) study revealed that common PCMT1 variants associate with hemolysis phenotypes and regulate PIMT protein level, as gleaned by protein quantitative trait loci (pQTL) analyses. The nonsynonymous rs4816 (V120I) allele, enriched in donors of Asian or African ancestry, emerged as a beneficial variant: carriers exhibited lower osmotic hemolysis, altered peptide methylation flux, and higher PIMT protein levels. Recombinant expression confirmed that the I120 variant displays preserved global folding, but greater catalytic activity than the canonical V120 enzyme. Transfusion outcome data showed that PCMT1 genotype influences hemoglobin increments and bilirubin responses in recipients. These findings identify PIMT as a novel determinant of RBC storage biology and establish rs4816 as a protective allele, with broader implications for donor diversity, transfusion efficacy, and proteome maintenance in aging.

Accurate HIV incidence estimates are essential for monitoring epidemic trends and evaluating prevention efforts. The limiting antigen (LAg) avidity enzyme immunoassay is the most widely used method to classify recent versus long-term HIV infections. The External Quality Assurance Oversight Laboratory (EQAPOL), in collaboration with Vitalant Research Institute, conducts a global External Quality Assurance (EQA) program to evaluate laboratory performance using commercial LAg kits. We assessed (i) the stability of calibrators and reagents from Sedia and Maxim kits over their shelf life, and (ii) the longitudinal consistency of EQA panel samples tested across nine proficiency rounds (2018-2023). Mixed-effects models were used to detect trends in optical density (OD) and normalized OD (ODn) values over time. No significant trends in OD or ODn were observed for either kit, and EQA panel samples showed stable reactivity across all rounds. Minor ODn shifts did not affect recency classification. Sedia kits consistently yielded slightly higher ODn values than Maxim kits, consistent with prior reports. These findings confirm the long-term reliability of both LAg assay kits and EQA panel materials, supporting the robustness of EQAPOL's quality assurance framework for accurate global HIV incidence surveillance.IMPORTANCEReliable estimation of HIV incidence depends on accurate classification of recent versus long-term infections, which in turn requires consistent assay performance and robust quality assurance. The External Quality Assurance Oversight Laboratory LAg External Quality Assurance program provides longitudinal monitoring of laboratory proficiency for two widely used commercial assays. By demonstrating the long-term consistency of calibrators, reagents, and quality control panels across multiple production lots and testing rounds, this study confirms the robustness of the global limiting antigen testing framework. These results strengthen confidence in the comparability of HIV incidence data across surveillance networks and geographic regions, supporting evidence-based decision-making for HIV prevention programs.

Abstract Sickle cell trait (SCT), the heterozygous state for the hemoglobin S (HbS) mutation, affects roughly 1 in 13 African American individuals and is common among blood donors recruited for antigen‐matched transfusions in sickle cell disease (SCD). While individuals with SCT are typically asymptomatic, it is unclear whether red blood cells (RBCs) from SCT donors have impaired storage quality and transfusion efficacy. Here, we integrate multi‐omics to characterize RBCs from donors SCT and evaluate their performance post‐transfusion. We first profiled RBCs from 174 HbAS and 248 HbAA volunteers, identifying elevated levels of metabolic markers of the storage lesion in SCT RBCs at baseline. We then interrogated the REDS RBC Omics dataset (>13,000 donors), identifying blood donors carrying the HbS E6V variants. SCT RBCs exhibited accelerated metabolic aging, oxidative stress, and proteostatic activation—phenotypes further exacerbated by storage duration and co‐inheritance of G6PD deficiency. Functional assays confirmed decreased osmotic fragility and increased oxidative hemolysis in SCT RBCs by storage Day 42. Pre‐clinically, stored RBCs from Townes mice carrying one allele of human sickle hemoglobin were characterized by a drop in post‐transfusion recovery compared to mice expressing canonical human hemoglobin. Clinically, analysis of 6828 transfusion events revealed that SCT RBCs were associated with lower hemoglobin increments 24 h post‐transfusion. These findings provide mechanistic and clinical evidence that SCT influences RBC quality and transfusion outcomes. Given the overrepresentation of SCT in donor pools serving patients with SCD, our study supports a more personalized approach to inventory management and transfusion strategies in high‐risk populations.

INTRODUCTION:SARS-CoV-2 infection is associated with hypercoagulability in patients with Coronavirus disease (COVID-19). We used a vein-to-vein database to examine the impact of transfusion of plasma units from blood donors with recent SARS-CoV-2 infection. STUDY DESIGN AND METHODS:We linked donor SARS-CoV-2 serology data with plasma transfusions occurring between 6/1/2020 and 3/31/2022. Using multivariable regression, we examined changes in the international normalized ratio (INR) and subsequent transfusion requirements following plasma transfusion relative to the timing of donor SARS-CoV-2 nucleocapsid antibody (anti-N Ab) positivity. RESULTS:We identified 2350 adults who received 5397 plasma units with donor SARS-CoV-2 serology data as part of 3721 plasma transfusion events. 8.1% (436/5397) of plasma units were from anti-N Ab positive donors, and median time from index seropositivity to donation was 89 days (interquartile range [IQR] 0-210). In recipients of plasma units from recently SARS-CoV-2 infected donors (<120 days), the adjusted odds of a 0.25 per unit lowering of the INR were increased (aOR 1.6 [1.1-2.5]; p = .03) and the odds of additional plasma transfusions within 24 h were decreased (aOR 0.6 [0.4-0.9]; p = .04). CONCLUSION:Recipients of plasma units from blood donors with recent SARS-CoV-2 infection were more likely to have post-transfusion reductions in the INR and less likely to require additional plasma transfusions.

BACKGROUND:The two largest US blood collection organizations led a multiphased, multicenter nationwide SARS-CoV-2 blood donor-based serosurveillance program. The potential impact of delayed sample processing and prolonged refrigerated or frozen storage on anti-SARS-CoV-2 antibody detection was investigated. METHODS:Anti-spike (S) IgG and anti-nucleocapsid (N) total immunoglobulin levels were compared for 20 paired plasma/serum samples tested fresh and frozen after separation from cellular components on Day 5 or after ≤40 days of 4°C storage; 10 paired plasma/serum samples separated on Day 5 and tested immediately or after ≤67 days of 4°C storage; and 85 plasma and 950 serum samples tested fresh on Day 1 and after ≤209 days of -20°C storage post-separation. Proportional Bland-Altman analyses were used to estimate average bias and 95% limits of agreement (LOA). RESULTS:Antibody reactivity was stable over time regardless of serum or plasma processing delays or prolonged refrigerated or frozen storage. Bland-Altman analyses suggest only minor deviations for anti-S antibodies for samples separated within 5 days and tested frozen compared to fresh (bias: 4.23%, 95% LOA: -10.02; 18.47), after ≤40 days of storage at 4°C pre-separation (9.51%, [-73.20; 92.22]) and after ≤67 days at 4°C post-separation (-14.04%, [-28.12; 0.04]). Similar observations were obtained for anti-N antibodies including samples retested after ≤209 days of storage at -20°C (-20.3%, [-81; 40.5]). CONCLUSION:Despite challenges encountered in sample access and processing during a rapidly evolving pandemic, sample processing variability and testing delays minimally impacted serologic results and thus provide evidence for the validity of results in studies requiring variable sample handling conditions.

The proportion of SARS-CoV-2 infections diagnosed by COVID-19 tests, including home antigen tests, is unknown. We detected infections among U.S. blood donors by testing for nucleocapsid antibody (anti-N) seroconversion and administered a questionnaire to determine the proportion of those infections that were associated with a self-reported positive COVID-19 test. Among U.S. blood donors with serologic evidence of SARS-CoV-2 infection who completed a survey, 47.7% reported an associated self-reported positive COVID-19 test. This proportion changed from July-December 2020 (44.9%) to July-December 2022 (54.8%). This study suggests many SARS-CoV-2 infections in adults are not diagnosed with a test.

BACKGROUND:Donor and red blood cell (RBC) component factors may affect patient outcomes after RBC transfusions, but data on the magnitude and consequences of these associations are limited. STUDY DESIGN AND METHODS:In this retrospective cohort study, we analyzed associations between 10 donor and component factors-including donor age, hemoglobin, parity, sex, and component storage time-and changes in 55 clinical laboratory markers measured within 24 h before and after RBC transfusions. Primary analyses used data from the Swedish SCANDAT3-S database, with findings replicated in the U.S. REDS-III database. The primary outcome was the transfusion-related change in pre- and post-transfusion values of the laboratory markers, normalized per RBC unit transfused. RESULTS:After adjusting for the false discovery rate, 33 significant associations were identified, with 20 replicated in the SCANDAT replication sample or the REDS-III cohort after Bonferroni corrections, and 18 remaining after visual assessment. Higher donor hemoglobin concentration consistently led to greater increases in recipient hemoglobin and measures of RBC mass. Extended component storage times were associated with elevated recipient bilirubin and carboxyhemoglobin levels. Differences in recipient hemoglobin response between the SCANDAT3-S and REDS-III cohorts suggest potential variations in transfusion efficacy across populations and practices. DISCUSSION:These findings suggest that considering donor hemoglobin and RBC component storage duration could enhance transfusion efficacy, providing avenues for personalized transfusion strategies to improve patient outcomes.

Caffeine is the most widely consumed psychoactive substance globally, yet its peripheral physiological effects remain incompletely understood. Leveraging comprehensive data from 13,091 blood donors in the REDS RBC-Omics study, we identified caffeine as a significant modulator of red blood cell (RBC) storage quality and transfusion outcomes. Elevated caffeine levels were reproducible across multiple donations from 643 recalled donors, selected based on their extremes in hemolytic propensity. Both in the screening and recalled cohorts, higher caffeine levels were associated with disrupted RBC metabolism, characterized by reduced glycolysis, depletion of adenylate pools or 2,3-bisphosphoglycerate, and increased markers of oxidative stress and osmotic fragility, including kynurenine accumulation. These observations were recapitulated in plasma and RBC of eight volunteers upon consumption of a cup of coffee independently of brewing method (Chemex vs. espresso). Clinically, elevated caffeine levels correlated with increased hemolysis and lower post-transfusion hemoglobin increments, an effect especially pronounced in recipients transfused with RBC from donors carrying common polymorphisms in the ADORA2B gene, a key regulator of RBC metabolism in hypoxia. These human findings were mechanistically validated using a murine model deficient in ADORA2b, which demonstrated impaired glycolytic flux, compromised antioxidant defenses (including caffeine-dependent direct inhibition of recombinantly expressed glucose 6-phosphate dehydrogenase), and decreased transfusion efficacy (lower hemoglobin increments, higher bilirubin after transfusion), effects further exacerbated by caffeine exposure during storage. Our study positions caffeine consumption as a modifiable factor in blood transfusion practice, advocating for precision strategies that integrate genetic and exposome factors, and identifies metabolic interventions to enhance blood quality and clinical outcomes.

Accurate timing estimates of when participants acquire HIV in HIV prevention trials are necessary for determining antibody levels at acquisition. The Antibody-Mediated Prevention (AMP) Studies showed that a passively administered broadly neutralizing antibody can prevent the acquisition of HIV from a neutralization-sensitive virus. We developed a pipeline for estimating the date of detectable HIV acquisition (DDA) in AMP Study participants using diagnostic and viral sequence data. Using a Bayesian strategy that combines three streams of data (REN [rev/vpu/env/Δnef] sequence, GP [gag/Δpol] sequence, and diagnostic) where their 95% credible intervals overlap based on pre-specified criteria and decision rules. We evaluated the performance of our AMP pipeline using PacBio viral sequence data from 41 participants across two prospective acute HIV acquisition cohort studies, FRESH and RV217, with twice-weekly sampling. These cohort studies enrolled young women in South Africa and men and women in Kenya and Thailand, respectively, with a high likelihood of HIV acquisition. In evaluating performance, "true DDA" was the center of bounds between last-negative and first-positive RNA diagnostic tests (median time 4 days, range 2-7 days); bias was the mean difference between estimated and true DDA. Using diagnostic data alone yielded timing estimates with a bias of 2.4 days and root mean square error (RMSE) of 7.9 days. These results were improved using sequence + diagnostic data (bias 1.5 days, RMSE 6.9 days), as well as by restricting sequence-based estimation to samples from ≤5 weeks post-DDA (bias 0.2 days, RMSE 7.8 days).IMPORTANCEIn HIV prevention trials, accurate timing estimates of when individual participants acquire HIV can be used to estimate antibody levels at the time of acquisition, which is useful for projecting antibody levels needed for prevention. The results we report here suggest that if sequence-based estimation of acquisition timing is used in future clinical trials of combination broadly neutralizing antibody (bnAb) regimens or multispecific bnAbs for HIV prevention, a sampling frequency of at least monthly is needed. Moreover, in the samples analyzed here, we observed less bias in sequence-based timing estimation for samples taken <5 weeks post-DDA. This observation is consistent with the timing of immune-driven selective pressures that may negatively impact the power to detect acquisition sieve effects.

BACKGROUND:In our previous study of blood donors in the Argentinian Chaco Province, we documented bimodal distributions of anti-Trypanosoma cruzi antibody (Ab) levels, suggesting potential self-cure in donors with low-reactive samples. This study aimed to correlate "high" and "low" Ab level groups, defined by a mathematical model, with parasitemia and electrocardiogram findings. Ab decline over time was also assessed. METHODOLOGY/ PRINCIPAL FINDINGS:We invited T. cruzi Ab reactive blood donors to enroll in the study from October 2018 to November 2019 with a follow up visit two years later. Blood samples were tested for T cruzi Ab by: Chagatest ELISA Lisado and Chagatest ELISA Recombinante v.4.0 (Wiener Lab, Argentina); VITROS Immunodiagnostic Products Anti-T.cruzi (Chagas) (Ortho-Clinical Diagnostics Inc., UK), and Architect Chagas (Abbott Laboratories, Germany). Target capture polymerase chain reaction (PCR) was performed on lysed whole blood samples from enrollment visits and electrocardiograms on second visits. Four hundred fifty donors were recruited, but 68 were excluded due to negative results on all study Ab assays. Ab level distributions were bimodal and classified as "high" or "low" at a calculated threshold for each of four assays. There were 160 donors with low and 179 with high Ab results on all assays. The remainder 43 were discordant reactive. Ninety-seven percentage of the PCR positive donors were among the concordant high Ab group. During the 2-4 year follow-up interval, relative Ab declines by three assays were significantly greater among those classified as low Ab and with negative PCR results. CONCLUSIONS/ SIGNIFICANCE:Ab reactivity is associated with PCR-detectable parasitemia. Greater Ab declines were detected among donors with low and/or discordant Ab reactivity and negative PCR results, suggesting spontaneous parasite clearance in these donors.

SARS-CoV-2 case surveillance in the United States did not distinguish first infections from reinfections. In a large blood donor cohort, self-reported first infections and reinfections during 2020-2022 mirrored public health case count surveillance, and reinfection incidence peaked in 2022. Blood donor data could aid in SARS-CoV-2 and emerging infectious disease surveillance.