Let's assume that the labs and their tests are 99% accurate.

The UCI did around 12000 tests last year, and about 380 came back
positive. These are just rough numbers off the top of my head.
It worked out to around 3.8% of all tests came back positive.

So, if you take that 99% accuracy number and apply it,
you end up with roughly 1 out of 3 positives due to bad testing.