Incidence of Vascular Thromboembolic Events in Outpatients with Mild COVID-19
Authors: Eswaran Harish , Jarmul Jamie , Shaheen Amy , Meaux David , Long Tristan , Saccoccio Derek , Moll Stephan 
Published: November 2020

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.