BackgroundCovid-19 is a triphasic disorder characterized by a viral phase lasting 7-10 days from onset of symptoms. In approximately 20% it is followed by a second stage heralded by elevation of pro- inflammatory markers such as ferritin, IL-6, CRP, LDH and D-dimers. We hypothesized that those with few abnormalities would have a low risk for progression to respiratory insufficiency and hence could be monitored at home without treatment.MethodsInclusion criteria included Covid infection, age >21, Oxygen saturation >90%. To be observed without treatment, patients could have no more than 1 of the following: CRP > 10 mg/dL, high LDH, ferritin > 500 ng/ml, D-dimer > 1 mg/L, IL-6 > 10 pg/ml, absolute lymphocyte count <1,000, Oxygen saturation <94%, or CT chest evidence of pneumonia. Primary endpoint was progression to respiratory failure and secondary endpoints was 28-day survival.ResultsOf 208 entered, 132 were low-risk and hence were monitored without therapy. None progressed to respiratory failure or died.ConclusionsWe have shown that our approach can identify cases who can safely be observed without treatment, thus avoiding expensive, potentially toxic therapies, and circumventing unnecessary, costly hospitalizations. These results support our hypothesis that applying our criteria, 64% of Covid-19 cases can be monitored as outpatients without therapy.What is already known about this subjectCOVID-19 is a triphasic disorder first typified by an infectious or viral phase that lasts from the first onset of symptoms until 7-10 days later. This is followed by a second phase considered as the inflammatory stage, characterized initially by the appearance of lung infiltrates which is followed in some cases by hypoxemia.Approximately 80% of patients never proceed to the second phase but currently there is no reliable and objective method to accurately predict those that are cured spontaneously without any treatment and who could be managed at home.What this study addsWe have developed an approach, based essentially on blood-based inflammatory markers which identifies low-risk cases that do not require therapy and can be managed at home. This method showed an excellent correlation with clinical outcome and has encouraging financial and psychological effects.Of 208 patients, 132, fulfilled criteria for low-risk disease that justified monitoring at home without therapy and none of these developed respiratory failure or any other significant complication.Included in this low-risk group were many cases with comorbidities, with COVID-19 pneumonia, as well as patients older than 65 and with more than two symptoms at presentation. These characteristics would usually portend an unfavourable prognosis, yet all these patients had an excellent outcome.