You wouldn't known how many cases came from a protest unless you test everyone or a truly representative sample a while after. In any case you wouldn't know unt

You wouldn't known how many cases came from a protest unless you test everyone or a truly representative sample a while after. In any case you wouldn't know until at least two weeks later, and then only with significant effort asking everyone whether they attended a specific protest (assuming they answer truthfully) and/or tracking people.