ABSTRACT
Real-time, reverse transcriptase PCR assays are a pervasive technology used for diagnosis of SARS-CoV-2 infection. These assays produce a cycle threshold value (Ct) corresponding to the first amplification cycle in which reliable amplification is detected. (1)Such Ct values have been used by clinicians and in public health settings to guide treatment, monitor disease progression, assess prognosis, and inform isolation practices. To understanding the risk of reporting out uncalibrated Ct values and potential for instead reporting out calibrated viral load values, we performed a multi-institutional study to benchmark major clinical platforms against a calibrated standard. We found that for any given Ct value, corresponding viral loads varied up to 1000-fold among the different tests. In contrast, when these different assays were calibrated against a common standard and then used to test unknown de-identified specimens at several dilutions, viral load values showed high precision between methods (standard deviation and range of 0.36 and 1.1 log10 genome copies) and high accuracy compared with droplet digital PCR (ddPCR) determinations (difference between mean CDC N2 and Sarbeco E ddPCR determinations and mean determinations by calibrated RT-PCR assays examined in our study of 0.044 log10 genome copies). We, therefore, find strong support for calibration of SARS-CoV-2 RT-PCR tests to allow conversion of cycle thresholds to accurate and precise viral load values that are reproducible across major clinical systems. Implementation of calibrated assays will provide more reliable information for clinical decision making and allow more rigorous interpretation of SARS-CoV-2 laboratory data in clinical and laboratory investigation.
ABSTRACT
BACKGROUNDChildren with SARS-CoV-2 infection typically have mild symptoms that do not require medical attention, leaving a gap in our understanding of the spectrum of illnesses that the virus causes in children. METHODSWe conducted a prospective cohort study of children and adolescents (<21 years of age) with a SARS-CoV-2-infected close contact. We collected nasopharyngeal or nasal swabs at enrollment and tested for SARS-CoV-2 using a real-time PCR assay. RESULTSOf 382 children, 289 (76%) were SARS-CoV-2-infected. SARS-CoV-2-infected children were more likely to be Hispanic (p<0.0001), less likely to have a history of asthma (p=0.009), and more likely to have an infected sibling contact (p=0.0007) than uninfected children. Children ages 6-13 years were frequently asymptomatic (38%) and had respiratory symptoms less often than younger children (30% vs. 49%; p=0.008) or adolescents (30% vs. 59%; p<0.0001). Compared to children ages 6-13 years, adolescents more frequently reported influenza-like (61% vs. 39%; p=0.002), gastrointestinal (26% vs. 9%; p=0.003), and sensory symptoms (43% vs. 9%; p<0.0001), and had more prolonged illnesses [median (IQR) duration: 7 (4, 12) vs. 4 (3, 8) days; p=0.004]. Despite the age-related variability in symptoms, we found no differences in nasopharyngeal viral load by age or between symptomatic and asymptomatic children. CONCLUSIONSHispanic ethnicity and an infected sibling close contact are associated with increased SARS-CoV-2 infection risk among children, while a history of asthma is associated with decreased risk. Age-related differences in the clinical manifestations of SARS-CoV-2 infection must be considered when evaluating children for COVID-19 and in developing screening strategies for schools and childcare settings.