inclusion criteria: inclusion criteria cohort a: * ≥ 18 years old * employee of healthcare organization in south dakota or sanford health employee in any location and with exposure to a person with covid-19 within the last 5 days * occupational exposure as determined by the participant's employee health department (i.e. not wearing the proper personal protective equipment (ppe)) * criteria according to center for disease control (cdc) guidelines * community exposure (within 6 feet for at least 15 minutes) * no current symptoms attributable to covid-19, per hcw report (fever, cough, difficulty breathing, sore throat) * no prior covid-19 positive diagnosis (eligible if previous testing is negative and meets all other inclusion and exclusion) * ability to provide informed consent inclusion criteria - cohort b * ≥ 18 years old * high-risk person who had close contact (i.e. within 6 feet for at least 15 minutes) with a covid-19 positive person within the last 5 days and is a south dakota resident or high-risk person with close household contact of a covid-19 positive sanford employee * high-risk person defined by: * age 18-44 with 2 or more comorbidities listed below * age 45-79 with any comorbid condition listed below * age 80 and above (regardless of comorbid conditions) * co-morbid list * congestive heart failure (chf) * chronic lung disease (includes any of the following: asthma, chronic obstructive pulmonary disease, emphysema) * solid organ transplant or immunosuppression (defined as an outpatient prescription of greater than 10 mg/day of prednisone or equivalent, use of chemotherapy, or use of immunosuppressive agents for solid organ transplant or for an autoimmune disease.) * chronic kidney disease or end stage renal disease * diabetes mellitus * cardiovascular disease/hypertension * smoking/vaping (currently using or history of using in the past 1 year) * obesity (calculated by height and weight per participant report) * hyperlipidemia * no current symptoms attributable to covid-19 * no prior covid-19 positive diagnosis (eligible if previous testing is negative and meets all other inclusion and exclusion) * ability to provide informed consent * confirmed review of concomitant medications (with emphasis on cardiac medications) exclusion criteria cohort a \& b: * known allergy to hydroxychloroquine or quinine * known history of long qt syndrome * known history of arrhythmia or dysrhythmia * known current qtc \>500 ms * known g6pd deficiency * known history of hypoglycemia * pregnant or nursing by patient history * use of any of the following concomitant medications: see appendix d for exclusion medication list * concurrent diagnosis of dermatitis, porphyria, or psoriasis * history of chronic liver disease, including cirrhosis and/or diagnosis of hepatitis (infectious, idiopathic, or immune) * history of chronic kidney disease * pre-existing retinopathy * already taking hydroxychloroquine * any condition or medication in the opinion of the investigator that would prohibit the use of hydroxychloroquine * enrollment in another clinical with investigational drug or device * inability to swallow pills * adults unable to provide informed consent

inclusion criteria: inclusion criteria cohort a: * ≥ 18 years old * employee of healthcare organization in south dakota or sanford health employee in any location and with exposure to a person with covid-19 within the last 5 days * occupational exposure as determined by the participant's employee health department (i.e. not wearing the proper personal protective equipment (ppe)) * criteria according to center for disease control (cdc) guidelines * community exposure (within 6 feet for at least 15 minutes) * no current symptoms attributable to covid-19, per hcw report (fever, cough, difficulty breathing, sore throat) * no prior covid-19 positive diagnosis (eligible if previous testing is negative and meets all other inclusion and exclusion) * ability to provide informed consent inclusion criteria - cohort b * ≥ 18 years old * high-risk person who had close contact (i.e. within 6 feet for at least 15 minutes) with a covid-19 positive person within the last 5 days and is a south dakota resident or high-risk person with close household contact of a covid-19 positive sanford employee * high-risk person defined by: * age 18-44 with 2 or more comorbidities listed below * age 45-79 with any comorbid condition listed below * age 80 and above (regardless of comorbid conditions) * co-morbid list * congestive heart failure (chf) * chronic lung disease (includes any of the following: asthma, chronic obstructive pulmonary disease, emphysema) * solid organ transplant or immunosuppression (defined as an outpatient prescription of greater than 10 mg/day of prednisone or equivalent, use of chemotherapy, or use of immunosuppressive agents for solid organ transplant or for an autoimmune disease.) * chronic kidney disease or end stage renal disease * diabetes mellitus * cardiovascular disease/hypertension * smoking/vaping (currently using or history of using in the past 1 year) * obesity (calculated by height and weight per participant report) * hyperlipidemia * no current symptoms attributable to covid-19 * no prior covid-19 positive diagnosis (eligible if previous testing is negative and meets all other inclusion and exclusion) * ability to provide informed consent * confirmed review of concomitant medications (with emphasis on cardiac medications) exclusion criteria cohort a \& b: * known allergy to hydroxychloroquine or quinine * known history of long qt syndrome * known history of arrhythmia or dysrhythmia * known current qtc \>500 ms * known g6pd deficiency * known history of hypoglycemia * pregnant or nursing by patient history * use of any of the following concomitant medications: see appendix d for exclusion medication list * concurrent diagnosis of dermatitis, porphyria, or psoriasis * history of chronic liver disease, including cirrhosis and/or diagnosis of hepatitis (infectious, idiopathic, or immune) * history of chronic kidney disease * pre-existing retinopathy * already taking hydroxychloroquine * any condition or medication in the opinion of the investigator that would prohibit the use of hydroxychloroquine * enrollment in another clinical with investigational drug or device * inability to swallow pills * adults unable to provide informed consent

inclusion criteria: inclusion criteria cohort a: - ≥ 18 years old - employee of healthcare organization in south dakota or sanford health employee in any location and with exposure to a person with covid-19 within the last 5 days - occupational exposure as determined by the participant's employee health department (i.e. not wearing the proper personal protective equipment (ppe)) - criteria according to center for disease control (cdc) guidelines - community exposure (within 6 feet for at least 15 minutes) - no current symptoms attributable to covid-19, per hcw report (fever, cough, difficulty breathing, sore throat) - no prior covid-19 positive diagnosis (eligible if previous testing is negative and meets all other inclusion and exclusion) - ability to provide informed consent inclusion criteria - cohort b - ≥ 18 years old - high-risk person who had close contact (i.e. within 6 feet for at least 15 minutes) with a covid-19 positive person within the last 5 days and is a south dakota resident or high-risk person with close household contact of a covid-19 positive sanford employee - high-risk person defined by: - age 18-44 with 2 or more comorbidities listed below - age 45-79 with any comorbid condition listed below - age 80 and above (regardless of comorbid conditions) - co-morbid list - congestive heart failure (chf) - chronic lung disease (includes any of the following: asthma, chronic obstructive pulmonary disease, emphysema) - solid organ transplant or immunosuppression (defined as an outpatient prescription of greater than 10 mg/day of prednisone or equivalent, use of chemotherapy, or use of immunosuppressive agents for solid organ transplant or for an autoimmune disease.) - chronic kidney disease or end stage renal disease - diabetes mellitus - cardiovascular disease/hypertension - smoking/vaping (currently using or history of using in the past 1 year) - obesity (calculated by height and weight per participant report) - hyperlipidemia - no current symptoms attributable to covid-19 - no prior covid-19 positive diagnosis (eligible if previous testing is negative and meets all other inclusion and exclusion) - ability to provide informed consent - confirmed review of concomitant medications (with emphasis on cardiac medications) exclusion criteria cohort a & b: - known allergy to hydroxychloroquine or quinine - known history of long qt syndrome - known history of arrhythmia or dysrhythmia - known current qtc >500 ms - known g6pd deficiency - known history of hypoglycemia - pregnant or nursing by patient history - use of any of the following concomitant medications: see appendix d for exclusion medication list - concurrent diagnosis of dermatitis, porphyria, or psoriasis - history of chronic liver disease, including cirrhosis and/or diagnosis of hepatitis (infectious, idiopathic, or immune) - history of chronic kidney disease - pre-existing retinopathy - already taking hydroxychloroquine - any condition or medication in the opinion of the investigator that would prohibit the use of hydroxychloroquine - enrollment in another clinical with investigational drug or device - inability to swallow pills - adults unable to provide informed consent

inclusion criteria: inclusion criteria cohort a: - ≥ 18 years old - employee of healthcare organization in south dakota or sanford health employee in any location and with exposure to a person with covid-19 within the last 5 days - occupational exposure as determined by the participant's employee health department (i.e. not wearing the proper personal protective equipment (ppe)) - criteria according to center for disease control (cdc) guidelines - community exposure (within 6 feet for at least 15 minutes) - no current symptoms attributable to covid-19, per hcw report (fever, cough, difficulty breathing, sore throat) - no prior covid-19 positive diagnosis (eligible if previous testing is negative and meets all other inclusion and exclusion) - ability to provide informed consent inclusion criteria - cohort b - ≥ 18 years old - high-risk person who had close contact (i.e. within 6 feet for at least 15 minutes) with a covid-19 positive person within the last 5 days and is a south dakota resident or high-risk person with close household contact of a covid-19 positive sanford employee - high-risk person defined by: - age 18-44 with 2 or more comorbidities listed below - age 45-79 with any comorbid condition listed below - age 80 and above (regardless of comorbid conditions) - co-morbid list - congestive heart failure (chf) - chronic lung disease (includes any of the following: asthma, chronic obstructive pulmonary disease, emphysema) - solid organ transplant or immunosuppression (defined as an outpatient prescription of greater than 10 mg/day of prednisone or equivalent, use of chemotherapy, or use of immunosuppressive agents for solid organ transplant or for an autoimmune disease.) - chronic kidney disease or end stage renal disease - diabetes mellitus - cardiovascular disease/hypertension - smoking/vaping (currently using or history of using in the past 1 year) - obesity (calculated by height and weight per participant report) - hyperlipidemia - no current symptoms attributable to covid-19 - no prior covid-19 positive diagnosis (eligible if previous testing is negative and meets all other inclusion and exclusion) - ability to provide informed consent - confirmed review of concomitant medications (with emphasis on cardiac medications) exclusion criteria cohort a & b: - known allergy to hydroxychloroquine or quinine - known history of long qt syndrome - known history of arrhythmia or dysrhythmia - known current qtc >500 ms - known g6pd deficiency - known history of hypoglycemia - pregnant or nursing by patient history - use of any of the following concomitant medications: see appendix d for exclusion medication list - concurrent diagnosis of dermatitis, porphyria, or psoriasis - history of chronic liver disease, including cirrhosis and/or diagnosis of hepatitis (infectious, idiopathic, or immune) - history of chronic kidney disease - pre-existing retinopathy - already taking hydroxychloroquine - any condition or medication in the opinion of the investigator that would prohibit the use of hydroxychloroquine - enrollment in another clinical with investigational drug or device - inability to swallow pills - adults unable to provide informed consent