Test, trace, isolate: evidence for declining SARS-CoV-2 PCR sensitivity in a clinical cohort.

Real-time reverse transcription-polymerase chain reaction (RT-PCR) on upper respiratory tract (URT) samples is the primary method to diagnose SARS-CoV-2 infections and guide public health measures, with a supportive role for serology. We reinforce previous findings on limited sensitivity of PCR testing, and solidify this fact by statistically utilizing a firm basis of multiple tests per individual. We integrate stratifications with respect to several patient characteristics such as severity of disease and time since onset of symptoms. Bayesian statistical modelling was used to retrospectively determine the sensitivity of RT-PCR using SARS-CoV-2 serology in 644 COVID-19-suspected patients with varying degrees of disease severity and duration. The sensitivity of RT-PCR ranged between 80% - 95%; increasing with disease severity, it decreased rapidly over time in mild COVID-19 cases. Negative URT RT-PCR results should be interpreted in the context of clinical characteristics, especially with regard to containment of viral transmission based on 'test, trace and isolate'. Keywords: SARS-CoV-2, RT-PCR, serology, sensitivity, public health.

Association between supine cerebral perfusion and symptomatic orthostatic hypotension.

The goal of this study was to investigate whether the supine resting perfusion of brain tissue in symptomatic patients suffering from orthostatic hypotension (OH) is changed compared to control subjects and whether an association exists between the resting perfusion and the severity of OH. Ten symptomatic OH patients and 8 control subjects were included in this study. One patient was retrospectively excluded because he suffered from multiple system atrophy. Systolic and diastolic blood pressure changes were measured during a tilting bed procedure. Cerebral blood flow, cerebral blood volume and mean transit time were determined by bolus-tracking perfusion MRI and correlated with blood pressure changes. Cerebral blood volume was significantly increased in OH patients compared with control subjects for white matter (P = 0.019) and the mean transit time was significantly increased for gray (P = 0.010) and white matter (P = 0.015). The cerebral blood flow of the gray (r = 0.74, P = 0.022) and white matter (r = 0.75, P = 0.020) was significantly, positively correlated with systolic blood pressure changes. The mean transit time in white matter was significantly, negatively correlated with systolic blood pressure changes (r = -0.68, P = 0.045). This study suggests that in symptomatic patients with OH the cerebral perfusion of the brain in the resting, supine position correlates with the severity of OH as measured by postural changes in blood pressure.