That approach makes sense for when you want a low false positive rate, i.e. when the treatment is dangerous or expensive (so you want to avoid it at all costs if it's unnecessary). Here, it's the other way around. Treatment is benign (stay at home unless it becomes an emergency), but a false negative is expensive (you'd infect lots of others). What cheap test do you know that can have a low false negative rate? The only one I know is the one that flags everyone as infected.

How does that help? Which results are you going to treat with low confidence for second pass and why? Positives? Negatives? Both? If both, then what's the point of first pass anyway?