From a press release in French via Google Translate:
Wednesday April 22, 2020
• First estimate of the prevalence of anti-SARS-CoV-2 IgG antibodies in the Geneva population • First validation of an automated platform for serological tests against the new coronavirus
I’m vague on the methodological details because the original report is in French. I gather they used an existing representative sample of the public, which is a good idea. Here in the U.S. we have many long term tracking projects like The Bell Curve’s National Longitudinal Study of Youth 1979, which is still going after 40 years. We know a huge amount about those people so getting a few thousand of them to volunteer to have blood tests would be more informative than building a new sample from scratch.
The University Hospitals of Geneva (HUG), more particularly the Population Epidemiology Unit of the Primary Care Medicine Service, the Center for Emerging Viral Diseases and the Laboratory Medicine Service, have conducted a study to estimate the prevalence of anti-SARS-CoV-2 IgG antibodies in a representative sample of the Geneva population. The minimum overall seroprevalence of 5.5% suggests that on April 17, 2020, approximately 27,000 people were exposed to SARS-CoV-2 in the canton of Geneva.
The (French-speaking) canton of Geneva officially has had 178 CV deaths. 178/27000 would be an infection fatality rate of 0.7%, although deaths lag infections so it is likely to get higher over time. Prevalence was estimated to be 3.5% on April 6-10, so that might suggest an IFR around 1%.
For whatever reason, deaths have been higher in Romance-speaking parts of Europe (other than Portugal) than in Germanic-speaking places.
Fortunately, though, daily deaths in Switzerland have been more or less declining over the last couple of weeks.
I presume medical care in Geneva is pretty good.
Previously, the HUG conducted a study to validate the performance of a high-throughput serological test platform that measures type G immunoglobulins (IgG) directed against SARS-CoV 2. It is the only facility to broadband (200 tests / hour) available today. The results of the study indicate that this test reliably confirms exposure to SARS-CoV-2 twenty days after the onset of symptoms. The platform is used for the aforementioned population study.
Seroprevalence surveys based on the detection of specific immunoglobulins type G (IgG) are of the utmost importance to know the proportion of the population that has already been exposed to the coronavirus. The presence of these immunoglobulins (antibodies) in the blood confirms that the person has been exposed to the virus. On the other hand, it does not allow the conclusion of total or partial immunity against the latter. Indeed, in the current state of knowledge, we know neither the rate of protection that this immunity confers against a new infection nor its possible duration. For this reason, the test is not yet accessible to the entire population.
In order to assess the seroprevalence of anti-SARS-CoV-2 antibodies in the canton of Geneva, the HUG launched a survey of a representative sample of the population. People who have already participated in the Bus Santé study (annual health survey of the canton’s population) were randomly selected and invited with their families to take a blood test and fill out a questionnaire. The study started on April 6, 2020 and continues until the end of May.
Preliminary results are based on the first 760 participants, i.e. 343 (54% women, 46% men, 87% adults and 13% minors) between April 6 and 10 and 417 participants (53% of women, 47% men, 87% adults and 13% minors) for the week of April 14 to 17, 2020.
These first data show a seroprevalence in the population estimated at 3.5% (possible variability from 1.6% to 5.4%) for the first week and 5.5% (possible variability from 3.3% to 7, 7%) for the second. This sample, as well as the period studied, is too small to deduce with certainty the percentage of weekly increase, but a significant increase was observed between the two weeks.
The overall seroprevalence of 5.5% suggests that nearly 27,000 people were exposed to SARS-CoV-2 in the canton of Geneva. This is a minimum estimate, probably linked to multiple uncertainties, including the time required to develop immunity and the dynamics of the epidemic. It is expected that this seroprevalence in the population will increase in the coming weeks due to the recent increase in the number of cases in the canton.
Here’s the rough draft (in French) of the paper.