Duration of viral infectiousness and correlation with symptoms and diagnostic testing in non-hospitalized adults during acute SARS-CoV-2 infection: A longitudinal cohort study

BACKGROUND

Guidelines for SARS-CoV-2 have relied on limited data on duration of viral infectiousness and correlation with COVID-19 symptoms and diagnostic testing.

METHODS

We enrolled ambulatory adults with acute SARS-CoV-2 infection and performed serial measurements of COVID-19 symptoms, nasal swab viral RNA, nucleocapsid (N) and spike (S) antigens, and replication-competent SARS-CoV-2 by viral growth in culture. We determined average time from symptom onset to a first negative test result and estimated risk of infectiousness, as defined by positive viral growth in culture.

RESULTS

Among 95 adults, median [interquartile range] time from symptom onset to first negative test result was 9 [5] days, 13 [6] days, 11 [4] days, and >19 days for S antigen, N antigen, culture growth, and viral RNA by RT-PCR, respectively. Beyond two weeks, virus growth and N antigen titers were rarely positive, while viral RNA remained detectable among half (26/51) of participants tested 21-30 days after symptom onset. Between 6-10 days from symptom onset, N antigen was strongly associated with culture positivity (relative risk=7.61, 95% CI: 3.01-19.22), whereas neither viral RNA nor symptoms were associated with culture positivity. During the 14 days following symptom onset, the presence of N antigen remained strongly associated (adjusted relative risk=7.66, 95% CI: 3.96-14.82) with culture positivity, regardless of COVID-19 symptoms.

CONCLUSIONS

Most adults have replication-competent SARS-CoV-2 for 10-14 after symptom onset. N antigen testing is a strong predictor of viral infectiousness and may be a more suitable biomarker, rather than absence of symptoms or viral RNA, to discontinue isolation within two weeks from symptom onset.

Performance of anterior nares and tongue swabs for nucleic acid, Nucleocapsid, and Spike antigen testing for detecting SARS-CoV-2 against nasopharyngeal PCR and viral culture

OBJECTIVES

This study assesses and compares the performance of different swab types and specimen collection sites for SARS-CoV-2 testing, to reference standard real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and viral culture.

METHODS

Symptomatic adults with COVID-19 who visited routine COVID-19 testing sites used spun polyester and FLOQSwabs to self-collect specimens from the anterior nares and tongue. We evaluated the self-collected specimen from anterior nares and tongue swabs for the nucleocapsid (N) or spike (S) antigen of SARS-CoV-2 by RT-PCR and then compared these results with results from RT-PCR and viral cultures from nurse-collected nasopharyngeal swabs.

RESULTS

Diagnostic sensitivity was highest for RT-PCR testing conducted using specimens from the anterior nares collected on FLOQSwabs (84%; 95% CI 68-94%) and spun polyester swabs (82%; 95% CI 66-92%), compared to RT-PCR tests conducted using specimens from nasopharyngeal swabs. Relative to viral culture from nasopharyngeal swabs, diagnostic sensitivities were higher for RT-PCR and antigen testing of anterior nares swabs (91-100%) than that of tongue swabs (18-81%). Antigen testing of anterior nares swabs had higher sensitivities against viral culture (91%) than against nasopharyngeal RT-PCR (38-70%). All investigational tests had high specificity compared with nasopharyngeal RT-PCR. Spun polyester swabs are equally effective as FLOQSwabs for anterior nasal RT-PCR testing.

CONCLUSIONS

We found that anterior nares specimens were more sensitive than tongue swab specimens or antigen testing for detecting SARS-CoV-2 by RT-PCR. Thus, self-collected anterior nares specimens may represent an alternative method for diagnostic SARS-CoV-2 testing in some settings.

Association of fludarabine pharmacokinetic/dynamic biomarkers with donor chimerism in nonmyeloablative HCT recipients

PURPOSE

Fludarabine monophosphate (fludarabine) is an integral component of many reduced-intensity conditioning regimens for hematopoietic cell transplantation (HCT). Fludarabine's metabolite, 9-β-D-arabinofuranosyl-2-fluoroadenine (F-ara-A), undergoes cellular uptake and activation to form the active cytotoxic metabolite fludarabine triphosphate (F-ara-ATP), which inhibits cellular DNA synthesis in CD4(+) and CD8(+) cells. In this study, we evaluated whether fludarabine-based pharmacologic biomarkers were associated with clinical outcomes in HCT recipients.

METHODS

Participants with hematologic diseases were conditioned with fludarabine and low-dose total body irradiation (TBI) followed by allogeneic HCT and post-grafting immunosuppression. After fludarabine administration, we evaluated pharmacological biomarkers for fludarabine-F-ara-A area under the curve (AUC) and the ratio of circulating CD4(+) and CD8(+) cells (CD4(+)/CD8(+) ratio) after fludarabine administration-in 102 patients; F-ara-ATP accumulation rate in enriched CD4(+) and CD8(+) cells was evaluated in 36 and 34 patients, respectively.

RESULTS

Interpatient variability in the pharmacological biomarkers was high, ranging from 3.7-fold (F-ara-A AUC) to 39-fold (F-ara-ATP in CD8(+) cells). Circulating CD8(+) cells were more sensitive to fludarabine administration. A population pharmacokinetic-based sampling schedule successfully allowed for estimation of F-ara-A AUC in this outpatient population. There was a poor correlation between the F-ara-AUC and the F-ara-ATP accumulation rate in CD4(+) (R (2) = 0.01) and CD8(+) cells (R (2) = 0.00). No associations were seen between the four biomarkers and clinical outcomes (day +28 donor T cell chimerism, acute graft-versus-host disease (GVHD), neutrophil nadirs, cytomegalovirus reactivation, chronic GVHD, relapse, non-relapse mortality, or overall mortality).

CONCLUSIONS

Considerable interpatient variability exists in pharmacokinetic and fludarabine-based biomarkers, but these biomarkers are not associated with clinical outcomes in fludarabine/TBI-conditioned patients.

Recipient pretransplant inosine monophosphate dehydrogenase activity in nonmyeloablative hematopoietic cell transplantation

Mycophenolic acid, the active metabolite of mycophenolate mofetil (MMF), inhibits inosine monophosphate dehydrogenase (IMPDH) activity. IMPDH is the rate-limiting enzyme involved in de novo synthesis of guanosine nucleotides and catalyzes the oxidation of inosine 5'-monophosphate to xanthosine 5'-monophosphate (XMP). We developed a highly sensitive liquid chromatography-mass spectrometry method to quantitate XMP concentrations in peripheral blood mononuclear cells (PMNCs) isolated from the recipient pretransplant and used this method to determine IMPDH activity in 86 nonmyeloablative allogeneic hematopoietic cell transplantation (HCT) patients. The incubation procedure and analytical method yielded acceptable within-sample and within-individual variability. Considerable between-individual variability was observed (12.2-fold). Low recipient pretransplant IMPDH activity was associated with increased day +28 donor T cell chimerism, more acute graft-versus-host disease (GVHD), lower neutrophil nadirs, and more cytomegalovirus reactivation but not with chronic GVHD, relapse, nonrelapse mortality, or overall mortality. We conclude that quantitation of the recipient's pretransplant IMPDH activity in PMNC lysate could provide a useful biomarker to evaluate a recipient's sensitivity to MMF. Further trials should be conducted to confirm our findings and to optimize postgrafting immunosuppression in nonmyeloablative HCT recipients.

Pharmacokinetic and pharmacodynamic analysis of inosine monophosphate dehydrogenase activity in hematopoietic cell transplantation recipients treated with mycophenolate mofetil

A novel approach to personalizing postgrafting immunosuppression in hematopoietic cell transplantation (HCT) recipients is evaluating inosine monophosphate dehydrogenase (IMPDH) activity as a drug-specific biomarker of mycophenolic acid (MPA)-induced immunosuppression. This prospective study evaluated total MPA, unbound MPA, and total MPA glucuronide plasma concentrations and IMPDH activity in peripheral blood mononuclear cells (PMNCs) at 5 time points after the morning dose of oral mycophenolate mofetil (MMF) on day +21 in 56 nonmyeloablative HCT recipients. Substantial interpatient variability in pharmacokinetics and pharmacodynamics was observed and accurately characterized by the population pharmacokinetic-dynamic model. IMPDH activity decreased with increasing MPA plasma concentration, with maximum inhibition coinciding with maximum MPA concentration in most patients. The overall relationship between MPA concentration and IMPDH activity was described by a direct inhibitory maximum effect model with an IC50 of 3.23 mg/L total MPA and 57.3 ng/mL unbound MPA. The day +21 IMPDH area under the effect curve (AUEC) was associated with cytomegalovirus reactivation, nonrelapse mortality, and overall mortality. In conclusion, a pharmacokinetic-dynamic model was developed that relates plasma MPA concentrations with PMNC IMPDH activity after an MMF dose in HCT recipients. Future studies should validate this model and confirm that day +21 IMPDH AUEC is a predictive biomarker.

Busulfan in infant to adult hematopoietic cell transplant recipients: a population pharmacokinetic model for initial and Bayesian dose personalization

PURPOSE

Personalizing intravenous busulfan doses to a target plasma concentration at steady state (Css) is an essential component of hematopoietic cell transplantation (HCT). We sought to develop a population pharmacokinetic model to predict i.v. busulfan doses over a wide age spectrum (0.1-66 years) that accounts for differences in age and body size.

EXPERIMENTAL DESIGN

A population pharmacokinetic model based on normal fat mass and maturation based on postmenstrual age was built from 12,380 busulfan concentration time points obtained after i.v. busulfan administration in 1,610 HCT recipients. Subsequently, simulation results of the initial dose necessary to achieve a target Css with this model were compared with pediatric-only models.

RESULTS

A two-compartment model with first-order elimination best fit the data. The population busulfan clearance was 12.4 L/h for an adult male with 62 kg normal fat mass (equivalent to 70 kg total body weight). Busulfan clearance, scaled to body size-specifically normal fat mass, is predicted to be 95% of the adult clearance at 2.5 years postnatal age. With a target Css of 770 ng/mL, a higher proportion of initial doses achieved the therapeutic window with this age- and size--dependent model (72%) compared with dosing recommended by the U.S. Food and Drug Administration (57%) or the European Medicines Agency (70%).

CONCLUSION

This is the first population pharmacokinetic model developed to predict initial i.v. busulfan doses and personalize to a target Css over a wide age spectrum, ranging from infants to adults.

A pilot pharmacologic biomarker study in HLA-haploidentical hematopoietic cell transplant recipients

PURPOSE

Eleven patients diagnosed with various hematologic malignancies receiving an HLA-haploidentical hematopoietic cell transplant (HCT) participated in an ancillary biomarker trial. The goal of the trial was to evaluate potential pharmacologic biomarkers pertinent to the conditioning regimen [fludarabine monophosphate (fludarabine) and cyclophosphamide (CY)] or postgrafting immunosuppression [CY and mycophenolate mofetil (MMF)] in these patients.

METHODS

We characterized the interpatient variability of nine pharmacologic biomarkers. The biomarkers evaluated were relevant to fludarabine (i.e., area under the curve (AUC) of 2-fluoro-ara-A or F-ara-A), CY (i.e., AUCs of CY and four of its metabolites), and MMF (i.e., total mycophenolic acid (MPA) AUC, unbound MPA AUC, and inosine monophosphate dehydrogenase (IMPDH) activity).

RESULTS

Interpatient variability in the pharmacologic biomarkers was high. Among those related to HCT conditioning, the interpatient variability ranged from 1.5-fold (CY AUC) to 4.0-fold (AUC of carboxyethylphosphoramide mustard, a metabolite of CY). Among biomarkers evaluated as part of postgrafting immunosuppression, the interpatient variability ranged from 1.7-fold (CY AUC) to 4.9-fold (IMPDH area under the effect curve). There was a moderate correlation (R (2) = 0.441) of within-patient 4-hydroxycyclophosphamide formation clearance.

CONCLUSIONS

Considerable interpatient variability exists in the pharmacokinetic and drug-specific biomarkers potentially relevant to clinical outcomes in HLA-haploidentical HCT recipients. Pharmacodynamic studies are warranted to optimize the conditioning regimen and postgrafting immunosuppression administered to HLA-haploidentical HCT recipients.

Nonrelapse mortality and mycophenolic acid exposure in nonmyeloablative hematopoietic cell transplantation

We evaluated the pharmacodynamic relationships between mycophenolic acid (MPA), the active metabolite of mycophenolate mofetil (MMF), and outcomes in 308 patients after nonmyeloablative hematopoietic cell transplantation. Patients were conditioned with total body irradiation ± fludarabine, received grafts from HLA-matched related (n = 132) or unrelated (n = 176) donors, and received postgrafting immunosuppression with MMF and a calcineurin inhibitor. Total and unbound MPA pharmacokinetics were determined to day 25; maximum a posteriori Bayesian estimators were used to estimate total MPA concentration at steady state (Css). Rejection occurred in 9 patients, 8 of whom had a total MPA Css less than 3 μg/mL. In patients receiving a related donor graft, MPA Css was not associated with clinical outcomes. In patients receiving an unrelated donor graft, low total MPA Css was associated with increased grades III to IV acute graft-versus-host disease and increased nonrelapse mortality but not with day 28 T cell chimerism, disease relapse, cytomegalovirus reactivation, or overall survival. We conclude that higher initial oral MMF doses and subsequent targeting of total MPA Css to greater than 2.96 μg/mL could lower grades III to IV acute graft-versus-host disease and nonrelapse mortality in patients receiving an unrelated donor graft.

Population pharmacokinetics and dose optimization of mycophenolic acid in HCT recipients receiving oral mycophenolate mofetil

We sought to create a population pharmacokinetic model for total mycophenolic acid (MPA), to study the effects of different covariates on MPA pharmacokinetics, to create a limited sampling schedule (LSS) to characterize MPA exposure (i.e., area under the curve or AUC) with maximum a posteriori Bayesian estimation, and to simulate an optimized dosing scheme for allogeneic hematopoietic cell transplantation (HCT) recipients. Four thousand four hundred ninety-six MPA concentration-time points from 408 HCT recipients were analyzed retrospectively using a nonlinear mixed effects modeling approach. MPA pharmacokinetics was characterized with a two-compartment model with first-order elimination and a time-lagged first-order absorption process. Concomitant cyclosporine and serum albumin were significant covariates. The median MPA clearance (CL) and volume of the central compartment were 24.2 L/hour and 36.4 L, respectively, for a 70 kg patient receiving tacrolimus with a serum albumin of 3.4 g/dL. Dosing simulations indicated that higher oral MMF doses are needed with concomitant cyclosporine, which increases MPA CL by 33.8%. The optimal LSS was immediately before and at 0.25 hours, 1.25 hours, 2 hours, and 4 hours after oral mycophenolate mofetil administration. MPA AUC in an individual HCT recipient can be accurately estimated using a five-sample LSS and maximum a posteriori Bayesian estimation.

Variation in prescribing patterns and therapeutic drug monitoring of intravenous busulfan in pediatric hematopoietic cell transplant recipients

Personalizing intravenous (IV) busulfan doses in children using therapeutic drug monitoring (TDM) is an integral component of hematopoietic cell transplant. The authors sought to characterize initial dosing and TDM of IV busulfan, along with factors associated with busulfan clearance, in 729 children who underwent busulfan TDM from December 2005 to December 2008. The initial IV busulfan dose in children weighing ≤12 kg ranged 4.8-fold, with only 19% prescribed the package insert dose of 1.1 mg/kg. In those children weighing >12 kg, the initial dose ranged 5.4-fold, and 79% were prescribed the package insert dose. The initial busulfan dose achieved the target exposure in only 24.3% of children. A wide range of busulfan exposures were targeted for children with the same disease (eg, 39 target busulfan exposures for the 264 children diagnosed with acute myeloid leukemia). Considerable heterogeneity exists regarding when TDM is conducted and the number of pharmacokinetic samples obtained. Busulfan clearance varied by age and dosing frequency but not by underlying disease. The authors- group is currently evaluating how using population pharmacokinetics to optimize initial busulfan dose and TDM (eg, limited sampling schedule in conjunction with maximum a posteriori Bayesian estimation) may affect clinical outcomes in children.

A limited sampling schedule to estimate mycophenolic Acid area under the concentration-time curve in hematopoietic cell transplantation recipients

Mycophenolate mofetil (MMF) is a key component of postgrafting immunosuppression in hematopoietic cell transplant (HCT) recipients. The plasma area under the curve (AUC) of its active metabolite, mycophenolic acid (MPA), is associated with MMF efficacy and toxicity. This study developed a population pharmacokinetic model of MPA in HCT recipients and created limited sampling schedules (LSSs) to enable individualized pharmacotherapy. A retrospective evaluation of MPA concentration-time data following a 2-hour MMF intravenous (IV) infusion was conducted in 77 HCT recipients. The final model consisted of 1 and 2 compartments for MMF and MPA pharmacokinetics, respectively. The mean estimated values (coefficient of variation, %) for total systemic clearance, distributional clearance, and central and peripheral compartment volumes of MPA were 36.9 L/h (34.5%), 15.3 L/h (80.4%), 11.9 L (71.7%), and 182 L (127%), respectively. No covariates significantly explained variability among individuals. Optimal LSSs were derived using a simulation approach based on the scaled mean squared error. A 5-sample schedule of 2, 2.5, 3, 5, and 6 hours from the start of the infusion precisely estimated MPA AUC(0-12 h) for Q12-hour IV MMF. A comparable schedule (2, 2.5, 3, 4, and 6 hours) similarly estimated MPA AUC(0-8) (h) for Q8-hour dosing.