[flaque]

That’s due to bayes theorem. If you test people who aren’t like to have caught the disease, and say the test has 1% chance to misdiagnose, you’ll almost certainly create wild amounts of false positives and spark a wider panic.

[leesec]

I think it's due to being extremely unprepared for the scale of testing required.

[allovernow]

The current test also has an absurdly high false negative rate - one source claims upwards of 50%.

https://www.bbc.com/news/health-51491763

[ithkuil]

"One possible explanation is the tests are accurate and the patients do not have coronavirus at the time of testing"

[allovernow]

Sure if you want to cherry pick explanations. Likelier alternative is this is a new virus and the test needs to be adapted for it. Also we don't know where to swab for it. Another paper came out saying presymptomatic patients have concentrations of virus in their sinuses IIRC.