Median age of cases dropping

THINK LIKE AN EPIDEMIOLOGIST:

What does it mean that the median age of new cases is dropping in some areas? I see three possible explanations, not all good. A thread on how to distinguish between them. 1/10

(Figure h/t @ScottGottliebMD) pic.twitter.com/Y6m45qoBL6

— Natalie E. Dean, PhD (@nataliexdean) June 23, 2020