There is already good evidence from South Korea, China and Italy that significant numbers of patients with proven COVID-19 infection have developed anosmia/hyposmia. In Germany it is reported that more than 2 in 3 confirmed cases have anosmia. In South Korea, where testing has been more widespread, 30% of patients testing positive have had anosmia as their major presenting symptom in otherwise mild cases.
https://www.entuk.org/loss-sense-smell-marker-covid-19-infection Loss of sense of smell (without a blocked nose) is a *strong* indicator of Covid19. Apparently otherwise asymptomatic carriers can lose their sense of smell as their only symptom. Immediately isolate to prevent transmission to friends/family/contacts. Tell others to beware of this symptom. In in a group of people who catch Covid19 one is likely to have the symptom, so it is a very important test to check for community transmission, especially since it seems to happen early and it is so simple and clear to recognise. Note that a common cause of anosmia is a viral infection (flu or cold), but it seems that it is a relatively rare symptom. Baysian, I would assume anyone with sudden loss of smell has Covid19, even if they are otherwise asymptomatic.
HN discussion here: https://news.ycombinator.com/item?id=22648580