Two papers (one non-peer reviewed, preprint) have reported that loss of smell (olfactory) and taste are a significant indication of COVID-19 infection.
A peer reviewed paper published in JAMA Otorhinolaryngology - Head and Neck Surgery titled, 'Sudden and Complete Olfactory Loss Function as a Possible Symptom of COVID-19' reports a case study of a patient who had sudden and complete loss of the olfactory function without nasal obstruction as the main symptom and was found positive for COVID-19.
The paper points to a similar report from the French Society of ENT.
Another non-peer reviewed preprint article published in MedRxiv entitled,'Loss of smell and taste in combination with other symptoms is a strong predictor of COVID-19 infection' reports that loss of smell and taste were present in 59% of COVID-19 positive individuals compared to 18% of those negative to the test, and that a combination of loss of smell and taste, fever, persistent cough, fatigue, diarrhoea, abdominal pain and loss of appetite is predictive of COVID-19 positive test.