Additional Study Information: If you currently live in the same household as someone who has tested positive for novel coronavirus (COVID-19), you might be eligible to participate in a trial that will test if a medicine used to prevent malaria, hydroxychloroquine, might reduce the risk of your developing COVID-19 symptoms. COVID-19 is a massive threat to public health worldwide. Post-exposure prophylaxis in other words, treating people who have been exposed to an infection in order to reduce the risk that they will develop the disease is a strategy that has been used successfully for seasonal influenza (e.g., Tamiflu) and HIV (e.g., "PEP"). Currently, there is no established post-exposure prophylaxis for persons at high risk of developing COVID-19. Hydroxychloroquine (brand name, Plaquenil), is a medicine that has been found to be effective against the novel coronavirus in recent experiments. Previously, hydroxychloquine has been safely used to prevent malaria and to treat autoimmune diseases. This study will test if a five-day treatment with hydroxychloroquine tablets reduces the risk of developing the symptoms of COVID-19. We will also screen you for certain medical conditions and medications, which could impact your eligibility for the study. If hydroxychloroquine is shown to reduce the risk of developing symptoms of COVID-19 among people at high risk of infection, this could help to reduce the morbidity and mortality of the COVID-19 epidemic. Please contact us for more information.