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A large Istat survey (64k) of the Italian population finds 2.5% seropositivity rate nationwide. Care homes residents not sampled and overall IFR based on clinically confirmed deaths (35k) comes to 2.3%. A few thoughts 1/n
Test kit characteristics: The survey was done over a two month period with the Abbott N-protein IgG kit. Issues with test kits primed to the NP-protein is discussed here and suggest poor ability to detect previous SARS-COV-2 infection >200 days POS. https://www.medrxiv.org/content/10.1101/2020.07.16.20155663v2.full.pdf 2/n
A sero kit targeting the spike protein esp. the spike trimer assays being more stable and providing much better sensitivity. Several studies have shown very stable (>95%) antibodies in longitudinal studies (>3 mths) when the spike trimer is used https://www.medrxiv.org/content/10.1101/2020.08.01.20166553v1 3/n
However, 41.7% of familial contacts of SARS-COV-2 confirmed cases were seropositive providing lower bounds for test kit sensitivity (~50%). True serop+ve rate is probably around 4-5% nationwide. This implies a crude 1.15-1.5% IFR. 4/n
The crude IFR estimates (not accounting for excess deaths) do not seem improbable given the unique epidemic situation in Italy in Late January to March. @DiseaseEcology gives a good summary of the data 5/n https://twitter.com/DiseaseEcology/status/1290754158438387713
However, as pointed out earlier in the thread and by others, they are several issues with the survey overall. For instance participation rate may be skewing the data substantially https://twitter.com/WesPegden/status/1290757276547125248 6/n
Overall, a more detailed report on the seropositive samples probably broken down by space-time should provide more data for deeper insights but it would be best if the repeat studies employ the use of a more sensitive kit to allow for more precise estimations. 7/n
