* prior diagnosis of covid-19 infection * participation in another covid-19 prophylaxis trial within 30 days of consent * respiratory illness with new-onset fever (temperature \> 100°f) or ongoing cough or dyspnea within 14 days * known allergy to hcq or chloroquine * congenital prolonged qt syndrome * current or planned use of qt prolonging drugs (e.g. procainamide, disopyramide, mexiletine, flecainide, propafenone, amiodarone, sotalol, cimetidine, dronedarone, dofetilide, levofloxacin, ciprofloxacin, moxifloxacin) and other contraindicated medications * end stage renal disease * pre-existing retinopathy * current or planned use of hydroxychloroquine (study drug) for any indication current or planned use of the following for treatment or prevention of covid-19 infection: * chloroquine * azithromycin * known cirrhosis or severe liver disease * history of severe skin reactions such as steven-johnson syndrome, toxic epidermal necrolysis * history of psoriasis or porphyria * ventricular arrhythmias requiring medical treatment * severe coronary artery disease or heart failure/cardiomyopathy with ongoing symptoms * current or planned use of use of anti-seizure drugs * history of glucose-6-phosphate dehydrogenase deficiency

* prior diagnosis of covid-19 infection * participation in another covid-19 prophylaxis trial within 30 days of consent * respiratory illness with new-onset fever (temperature \> 100°f) or ongoing cough or dyspnea within 14 days * known allergy to hcq or chloroquine * congenital prolonged qt syndrome * current or planned use of qt prolonging drugs (e.g. procainamide, disopyramide, mexiletine, flecainide, propafenone, amiodarone, sotalol, cimetidine, dronedarone, dofetilide, levofloxacin, ciprofloxacin, moxifloxacin) and other contraindicated medications * end stage renal disease * pre-existing retinopathy * current or planned use of hydroxychloroquine (study drug) for any indication current or planned use of the following for treatment or prevention of covid-19 infection: * chloroquine * azithromycin * known cirrhosis or severe liver disease * history of severe skin reactions such as steven-johnson syndrome, toxic epidermal necrolysis * history of psoriasis or porphyria * ventricular arrhythmias requiring medical treatment * severe coronary artery disease or heart failure/cardiomyopathy with ongoing symptoms * current or planned use of use of anti-seizure drugs * history of glucose-6-phosphate dehydrogenase deficiency

- prior diagnosis of covid-19 infection - participation in another covid-19 prophylaxis trial within 30 days of consent - respiratory illness with new-onset fever (temperature > 100°f) or ongoing cough or dyspnea within 14 days - known allergy to hcq or chloroquine - congenital prolonged qt syndrome - current or planned use of qt prolonging drugs (e.g. procainamide, disopyramide, mexiletine, flecainide, propafenone, amiodarone, sotalol, cimetidine, dronedarone, dofetilide, levofloxacin, ciprofloxacin, moxifloxacin) and other contraindicated medications - end stage renal disease - pre-existing retinopathy - current or planned use of hydroxychloroquine (study drug) for any indication current or planned use of the following for treatment or prevention of covid-19 infection: - chloroquine - azithromycin - known cirrhosis or severe liver disease - history of severe skin reactions such as steven-johnson syndrome, toxic epidermal necrolysis - history of psoriasis or porphyria - ventricular arrhythmias requiring medical treatment - severe coronary artery disease or heart failure/cardiomyopathy with ongoing symptoms - current or planned use of use of anti-seizure drugs - history of glucose-6-phosphate dehydrogenase deficiency

- prior diagnosis of covid-19 infection - participation in another covid-19 prophylaxis trial within 30 days of consent - respiratory illness with new-onset fever (temperature > 100°f) or ongoing cough or dyspnea within 14 days - known allergy to hcq or chloroquine - congenital prolonged qt syndrome - current or planned use of qt prolonging drugs (e.g. procainamide, disopyramide, mexiletine, flecainide, propafenone, amiodarone, sotalol, cimetidine, dronedarone, dofetilide, levofloxacin, ciprofloxacin, moxifloxacin) and other contraindicated medications - end stage renal disease - pre-existing retinopathy - current or planned use of hydroxychloroquine (study drug) for any indication current or planned use of the following for treatment or prevention of covid-19 infection: - chloroquine - azithromycin - known cirrhosis or severe liver disease - history of severe skin reactions such as steven-johnson syndrome, toxic epidermal necrolysis - history of psoriasis or porphyria - ventricular arrhythmias requiring medical treatment - severe coronary artery disease or heart failure/cardiomyopathy with ongoing symptoms - current or planned use of use of anti-seizure drugs - history of glucose-6-phosphate dehydrogenase deficiency