Because of the diverse etiologies of community-acquired pneumonia (CAP) and the limitations of current diagnostic modalities, serum procalcitonin levels have been proposed as a novel tool to guide antibiotic therapy. Outcome data from procalcitonin-guided therapy trials have shown similar mortality, but the essential question is whether the sensitivity and specificity of procalcitonin levels enable the practitioner to distinguish bacterial pneumonia, which requires antibiotic therapy, from viral pneumonia, which does not. In this meta-analysis of 12 studies in 2408 patients with CAP that included etiologic diagnoses and sufficient data to enable analysis, the sensitivity and specificity of serum procalcitonin were 0.55 (95% confidence interval [CI], .37–.71; I2 = 95.5%) and 0.76 (95% CI, .62–.86; I2 = 94.1%), respectively. Thus, a procalcitonin level is unlikely to provide reliable evidence either to mandate administration of antibiotics or to enable withholding such treatment in patients with CAP.

Body size and development time are important life history traits because they are often highly correlated with fitness. Although the developmental mechanisms that control growth have been well studied, the mechanisms that control how a species-characteristic body size is achieved remain poorly understood. In insects adult body size is determined by the number of larval molts, the size increment at each molt, and the mechanism that determines during which instar larval growth will stop. Adult insects do not grow, so the size at which a larva stops growing determines adult body size. Here we develop a quantitative understanding of the kinetics of growth throughout larval life of Manduca sexta, under different conditions of nutrition and temperature, and for genetic strains with different adult body sizes. We show that the generally accepted view that the size increment at each molt is constant (Dyar’s Rule) is systematically violated: there is actually a progressive increase in the size increment from instar to instar that is independent of temperature. In addition, the mass-specific growth rate declines throughout the growth phase in a temperature-dependent manner. We show that growth within an instar follows a truncated Gompertz trajectory. The critical weight, which determines when in an instar a molt will occur, and the threshold size, which determines which instar is the last, are different in genetic strains with different adult body sizes. Under nutrient and temperature stress Manduca has a variable number of larval instars and we show that this is due to the fact that more molts at smaller increments are taken before threshold size is reached. We test whether the new insight into the kinetics of growth and size determination are sufficient to explain body size and development time through a mathematical model that incorporates our quantitative findings.

Background Coronavirus disease 2019 (COVID‐19) is associated with high rates of thromboembolic events in hospitalized patients. It remains to be determined if this risk persists following hospital discharge. Methods We conducted a retrospective cohort study of outpatients recently hospitalized for COVID‐19 to determine the incidence of vascular thromboembolic events within 30 days of discharge. We investigated the risk factors associated with these events, including intensive care admission, age, and anticoagulation. Results Among 447 patients hospitalized for COVID‐19, 2.0% experienced a vascular thromboembolic event within 30 days of discharge. No risk factor variable was significantly associated with an increased risk for these events. Conclusions The incidence of vascular thromboembolic events following hospital discharge for COVID‐19 is low. These findings suggest against the routine use of postdischarge thromboprophylaxis in patients with COVID‐19.

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Livedoid vasculopathy (LV) is a rare thrombotic vasculopathy of the dermis characterized by painful, relapsing ulcers over the lower extremities. Diagnosis is challenging due to the overlap in clinical appearance and nomenclature with other skin disorders. Treatment selection is complicated by poor understanding of the pathogenesis of LV and lack of robust clinical trials evaluating therapy efficacy. The terminology and pathophysiology of LV are reviewed here, along with its epidemiology, clinical and histologic features, and treatment options. A diagnostic pathway is suggested to guide providers in evaluating for comorbidities, referring to appropriate specialists, and choosing from the available classes of therapy.

Introduction Hypercoagulability is a hallmark of COVID-19, the disease caused by the severe acute respiratory syndrome coronavirus 2 (Sars-CoV-2).1 While studies have investigated vascular thromboembolic events (VaTE) in critically ill and hospitalized patients with COVID-19, less is known about thrombotic complications in patients with mild symptoms.2 Our current institutional management protocol recommends prophylactic anticoagulation for COVID-19 patients admitted to the hospital but not for outpatients with less severe disease. We evaluated the incidence of VaTE in outpatients diagnosed with COVID-19 at our institution in order to assess the potential need for thromboprophylaxis in outpatient COVID-19 management. Methods We conducted a retrospective analysis of electronic medical record data of outpatients in the University of North Carolina Health System who tested positive for Sars-CoV-2 between March 15 and June 20, 2020. Patients were diagnosed at one of 17 ambulatory respiratory diagnostic centers (n=706), or diagnosed and subsequently discharged from one of 11 emergency departments (n=1967) in the UNC system. Diagnosis was made using reverse transcriptase polymerase chain reaction testing of nasopharyngeal or oropharyngeal swab samples. The study outcome was the diagnosis of a vascular thromboembolic event within 30 days of COVID-19 diagnosis. This included deep vein thrombosis, pulmonary embolism, superficial thrombophlebitis, myocardial infarction, ischemic stroke, and systemic arterial thromboembolism. VaTE was defined based on documentation of an associated ICD-10 code in the patient's electronic medical record within the specified time frame. Outcomes data were reported as incidence rates for the entire study population. Results 2673 outpatients were diagnosed with COVID-19 in the study period. The mean age for this cohort was 37.9 ± 17.3 years and 54% were female. 20 unique individuals (0.7%) experienced a VaTE within 30 days of diagnosis. Of these, 3 (15%) experienced venous thromboembolic events, 16 (80%) experienced arterial events, and 1 patient experienced both. Mean time to VaTE was 12.8 ± 9.3 days. Within 30 days of diagnosis, 188 of these patients (7%) had an emergency department visit or experienced hospital observation or inpatient admission. Conclusions We found that the incidence of VaTE in outpatients with mild COVID-19 is low. Limitations of this study include that patients were not routinely screened for VaTE and may have sought treatment for thrombotic complications outside the hospital system. This may have led to an underestimate of the true incidence; however, the findings are in line with data showing that non-hospitalized COVID-19 patients tend to be younger and have fewer medical comorbidities than hospitalized patients.3 This argues against the routine use of thromboprophylaxis in outpatients with COVID-19. References 1. Hippensteel JA, Burnham EL, Jolley SE. Prevalence of venous thromboembolism in critically ill patients with COVID-19. British Journal of Haematology. 2020; 190(3):e134-e137. 2. Emert R, Shah P, Zampella JG. COVID-19 and hypercoagulability in the outpatient setting. Thrombosis Research. 2020; 192:122-123. 3. Killerby ME, Link-Gelles R, Haight SC, et al. Characteristics associated with hospitalization among patients with COVID-19 - metropolitan Atlanta, Georgia, March-April 2020. Morbidity and Mortality Weekly Report. 2020; 69(25):790-794. Disclosures No relevant conflicts of interest to declare.

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Livedoid vasculopathy (LV) is an ulcerative disorder of the lower extremities characterized by dermal vessel thrombosis with unclear cause. Recent reports of LV-associated upper extremity peripheral neuropathy and epineurial thrombosis suggest a systemic etiology for the condition. We sought to outline the characteristics of peripheral neuropathy in patients with LV. Cases of LV with concurrent peripheral neuropathy and reviewable electrodiagnostic testing reports were identified by electronic medical record database query and examined in detail. Of 53 patients with LV, 33 (62%) had peripheral neuropathy, 11 had reviewable electrodiagnostic reports, and 6 had no clear alternative explanation for neuropathy. Distal symmetric polyneuropathy was the most commonly observed pattern of neuropathy (n ¼ 3) followed by mononeuropathy multiplex (n ¼ 2). Most patients experienced symptoms in both upper and lower extremities (n ¼ 4). Peripheral neuropathy is common in patients with LV. Whether this association is reflective of a systemic, prothrombotic etiology remains to be determined.