COVID-19 Outbreak (Update: More than 2.9M cases and 132,313 deaths in US)

Look at it this way: the UK is testing people with symptoms, mostly hospital admissions at this point. If we take the last five days, around 18% of those have been positive. That really doesn't seem to fit with the notion of 50% of the UK having been exposed to it, does it?

Exactly. The whole thing is total nonsense. The only people being tested in most countries are the very most likely cases, and they're coming in at less than 1 in 5 of those being positive. I do think the numbers are much higher than the cases being reported, but they're nowhere near 50%. Maybe if you drop the a zero off of that number you're getting warmer.