Most individuals who are positive, who have been exposed, show up with their symptoms early, in the first three to five days, post exposure. You can track people in terms of, “My family member was positive. I was exposed.” Their detectable viral load is often 48 hours to 72 hours before symptom onset, so you can kind of map out, from the gross majority of individuals, that they will show up positive by day 10 and they will have detectable virus by day seven. That's where that consolidation comes out and where the CDC guidelines have changed in the sense that you might miss 1% in that tail between 10 to 14 days, but it's very unclear if that's even clinically relevant in most individuals. If you release people by day 10 who are asymptomatic, you probably have caught most of your individuals there. If you want to release them earlier, by day seven most of those people who are symptomatic by day 10 should probably have a detectable PCR or molecular result at that point.
That's where that advice has come from. It's an evolving field. Again, 14 days was the standard from the beginning, but again, knowing the natural history studies of people after exposure, it's much more likely that the gross majority of individuals will be PCR positive by day seven and positive for symptoms by day 10.