inclusion criteria (index cases): - age >=18 years old and - sars-cov-2 positive and - well enough to self-isolate at home (at an address in switzerland) and - at risk of complications from covid-19 i.e. one or more of the following - age >=65 years - hypertension - diabetes - cardiovascular disease (history of infarction or peripheral arteriopathy or cerebrovascular accident or cardiac insufficiency) - chronic respiratory disease - immunosuppression - cancer - obesity (bmi>40) exclusion criteria (index cases): - allergy to hydroxychloroquine/4-aminoquinilones - retinal eye disease - known chronic kidney disease, stage 4 or 5 or receiving dialysis - weight < 40 kg - known porphyria - known psoriasis - known myasthenia gravis - taking drugs with moderate-severe interactions with hcq - taking ≥ 2 qt prolonging drugs - taking 1 qt prolonging drug and a loop diuretic - moderate or severe heart failure - severe or uncontrolled arrhythmia - recent myocardial infarction or stroke (past 6 months) - current pregnancy - current hospitalisation - known hemolytic anaemia inclusion criteria (household contacts): - age >1 year old and - living in same household as index case during self-isolation exclusion criteria (household contacts): - history of laboratory-confirmed sars-cov-2 infection

inclusion criteria (index cases): - age >=18 years old and - sars-cov-2 positive and - well enough to self-isolate at home (at an address in switzerland) and - at risk of complications from covid-19 i.e. one or more of the following - age >=65 years - hypertension - diabetes - cardiovascular disease (history of infarction or peripheral arteriopathy or cerebrovascular accident or cardiac insufficiency) - chronic respiratory disease - immunosuppression - cancer - obesity (bmi>40) exclusion criteria (index cases): - allergy to hydroxychloroquine/4-aminoquinilones - retinal eye disease - known chronic kidney disease, stage 4 or 5 or receiving dialysis - weight < 40 kg - known porphyria - known psoriasis - known myasthenia gravis - taking drugs with moderate-severe interactions with hcq - taking ≥ 2 qt prolonging drugs - taking 1 qt prolonging drug and a loop diuretic - moderate or severe heart failure - severe or uncontrolled arrhythmia - recent myocardial infarction or stroke (past 6 months) - current pregnancy - current hospitalisation - known hemolytic anaemia inclusion criteria (household contacts): - age >1 year old and - living in same household as index case during self-isolation exclusion criteria (household contacts): - history of laboratory-confirmed sars-cov-2 infection