UK recently corrected their backlog of infections by adding 16k extra Covid cases over the last 6 months. Citing IT failure as reason. That was a 25% under reporting.
What actually happened?
Testers sent data in CSV files -- ok.
Central data was stored in a database -- ok.
For exporting CSV files into the database they used Excel which limited rows to 64k max. -- That silently chopped off all cases after the first 1400 person in each file -- not ok.
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https://www.bbc.com/news/technology-54423988