Geneva is conducting an 8 week seroprevalance study and the authors released preliminary results from the first three weeks. By the third week of the study (April 20-24), almost 10% of the population tested positive, with the numbers increasing rapidly from week 1 to week 3:
The authors excluded (actually deferred) individuals who had symptoms or were in quarantine or isolation, so their numbers may underestimate the true prevalance. The authors don't estimate an IFR, but a reddit thread has some interesting details, including an IFR estimate of about 0.49% (or slightly higher or lower depending on assumptions used for lag times of antibody test and fatalities).
According to one post, the fatalities in Geneva are heavily concentrated in the over 80 age group, with only 2 fatalities in the under 50 age group:
30-39 years: 2
50-59 years: 6
60-69 years: 11
70-79 years: 46
80+ years: 180
All others are 0
Repeated seroprevalence of anti-SARS-CoV-2 IgG antibodies in a population-based sample from Geneva, Switzerland : COVID19
Will be interesting to watch as there are five more weeks of testing to conduct/analyze in the study.