* increased risk of bleeding such as a) significant bleeding in the last 3 months; b) active gastroduodenal ulcer in the last 3 months; c) history of bronchiectasis or pulmonary cavitation; d) need for dual antiplatelet therapy or anticoagulation; e) prior intracranial hemorrhage, f) known severe thrombocytopenia g) active cancer and undergoing treatment * any illness or condition that in the opinion of the investigator would significantly increase the risk of bleeding (example recent trauma, recent surgery, severe uncontrolled hypertension, gastrointestinal cancer, renal failure requiring dialysis, severe liver disease, known bleeding diathesis) * known allergies, hypersensitivity, or intolerance to rivaroxaban or its excipients * positive covid-19 antibody or serology test after 2-week period of acute, symptomatic covid-19 infection * known diagnosis of triple positive (positive for lupus anticoagulant, anticardiolipin, and anti-beta 2-glycoprotein i antibodies) antiphospholipid syndrome

* increased risk of bleeding such as a) significant bleeding in the last 3 months; b) active gastroduodenal ulcer in the last 3 months; c) history of bronchiectasis or pulmonary cavitation; d) need for dual antiplatelet therapy or anticoagulation; e) prior intracranial hemorrhage, f) known severe thrombocytopenia g) active cancer and undergoing treatment * any illness or condition that in the opinion of the investigator would significantly increase the risk of bleeding (example recent trauma, recent surgery, severe uncontrolled hypertension, gastrointestinal cancer, renal failure requiring dialysis, severe liver disease, known bleeding diathesis) * known allergies, hypersensitivity, or intolerance to rivaroxaban or its excipients * positive covid-19 antibody or serology test after 2-week period of acute, symptomatic covid-19 infection * known diagnosis of triple positive (positive for lupus anticoagulant, anticardiolipin, and anti-beta 2-glycoprotein i antibodies) antiphospholipid syndrome

- increased risk of bleeding such as a) significant bleeding in the last 3 months; b) active gastroduodenal ulcer in the last 3 months; c) history of bronchiectasis or pulmonary cavitation; d) need for dual antiplatelet therapy or anticoagulation; e) prior intracranial hemorrhage, f) known severe thrombocytopenia g) active cancer and undergoing treatment - any illness or condition that in the opinion of the investigator would significantly increase the risk of bleeding (example recent trauma, recent surgery, severe uncontrolled hypertension, gastrointestinal cancer, renal failure requiring dialysis, severe liver disease, known bleeding diathesis) - known allergies, hypersensitivity, or intolerance to rivaroxaban or its excipients - positive covid-19 antibody or serology test after 2-week period of acute, symptomatic covid-19 infection - known diagnosis of triple positive (positive for lupus anticoagulant, anticardiolipin, and anti-beta 2-glycoprotein i antibodies) antiphospholipid syndrome

- increased risk of bleeding such as a) significant bleeding in the last 3 months; b) active gastroduodenal ulcer in the last 3 months; c) history of bronchiectasis or pulmonary cavitation; d) need for dual antiplatelet therapy or anticoagulation; e) prior intracranial hemorrhage, f) known severe thrombocytopenia g) active cancer and undergoing treatment - any illness or condition that in the opinion of the investigator would significantly increase the risk of bleeding (example recent trauma, recent surgery, severe uncontrolled hypertension, gastrointestinal cancer, renal failure requiring dialysis, severe liver disease, known bleeding diathesis) - known allergies, hypersensitivity, or intolerance to rivaroxaban or its excipients - positive covid-19 antibody or serology test after 2-week period of acute, symptomatic covid-19 infection - known diagnosis of triple positive (positive for lupus anticoagulant, anticardiolipin, and anti-beta 2-glycoprotein i antibodies) antiphospholipid syndrome