Redesigning SARS-CoV-2 clinical RT-qPCR assays for wastewater RT-ddPCR

COVID-19 wastewater surveillance has gained widespread acceptance to monitor community infection trends. Wastewater samples primarily differ from clinical samples by having low viral concentrations due to dilution, and high levels of PCR inhibitors. Therefore, wastewater samples should be processed by appropriately designed and optimized molecular workflows to accurately quantify targets. Digital PCR has shown to be more sensitive and resilient to environmental matrix inhibition. However, most SARS-CoV-2 assays have been designed for clinical use on RT-qPCR instruments, then adopted to digital PCR platforms. But it is unknown whether clinical RT-qPCR assays are adequate to use on digital PCR platforms. Here we designed an N and E gene multiplex (ddCoV_N and ddCoV_E) specifically for RT-ddPCR and benchmarked them against the nCoV_N2 and E_Sarbeco assays. ddCoV_N and ddCoV_E have equivalent limits of detections and wastewater sample concentrations to NCoV_N2 and E_Sarbeco but showed improved signal-to-noise ratios that eased interpretation and ability to multiplex. From GISAID downloaded unique sequences analyzed, 2.12% and 0.83% present a mismatch or would not be detected by the used primer/probe combination for the ddCoV_N and ddCoV_E, respectively.

Wastewater SARS-CoV-2 Concentration and Loading Variability from Grab and 24-Hour Composite Samples

The ongoing COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) requires a significant, coordinated public health response. Assessing case density and spread of infection is critical and relies largely on clinical testing data. However, clinical testing suffers from known limitations, including test availability and a bias towards enumerating only symptomatic individuals. Wastewater-based epidemiology (WBE) has gained widespread support as a potential complement to clinical testing for assessing COVID-19 infections at the community scale. The efficacy of WBE hinges on the ability to accurately characterize SARS-CoV-2 RNA concentrations in wastewater. To date, a variety of sampling schemes have been used without consensus around the appropriateness of grab or composite sampling. Here we address a key WBE knowledge gap by examining the variability of SARS-CoV-2 RNA concentrations in wastewater grab samples collected every 2 hours for 72 hours compared with three corresponding 24-hour flow-weighted composite samples collected over the same period. Results show relatively low variability (respective means for N1, N2, N3 assays = 608, 847.9, 768.4 copies 100 mL-1, standard deviations = 501.4, 500.3, 505.8 copies 100 mL-1) for grab sample concentrations, and good agreement between most grab samples and their respective composite (mean deviation from composite = 159 copies 100 mL-1). When SARS-CoV-2 RNA concentrations are used to calculate viral load (RNA concentration * total influent flow the sample day), the discrepancy between grabs (log10 range for all grabs = 11.9) or a grab and its associated 24-hour composite (log10 difference = 11.6) are amplified. A similar effect is seen when estimating carrier prevalence in a catchment population with median estimates based on grabs ranging 63-1885 carriers. Findings suggest that grab samples may be sufficient to characterize SARS-CoV-2 RNA concentrations, but additional calculations using these data may be sensitive to grab sample variability and warrant the use of flow-weighted composite sampling. These data inform future WBE work by helping determine the most appropriate sampling scheme and facilitate sharing of datasets between studies via consistent methodology.

Hypersensitivity Reaction as a Harbinger of Acute Myeloid Leukemia: A Case Report and Review of the Literature

Cutaneous paraneoplastic syndromes comprise a broad spectrum of cutaneous reactions to an underlying malignancy. These dermatoses are not the result of metastatic spread to the skin, but rather a reaction to the presence of malignancy. Cutaneous paraneoplastic syndromes often precede the identification of a malignancy. We describe the case of a 79-year-old man with a six-month history of recalcitrant treatment- resistant dermatitis. A complete blood count test performed at the time of initial presentation was normal. The patient ultimately presented with erythroderma and was diagnosed with acute myeloid leukemia (AML). The evolution of the dermatitis to erythroderma coincided with the clinical presentation of AML, and was therefore considered to be a paraneoplastic syndrome. The patient decided against therapy and died seven weeks after diagnosis. Physicians should consider a cutaneous paraneoplastic syndrome when faced with dynamic recalcitrant dermatoses that are difficult to treat and decide on laboratory testing accordingly. Patients should be evaluated regularly for two to three years after initial diagnosis with a physical exam and review of systems to monitor for signs and symptoms of malignancy.