http://permaculturenews.org/20...

Suggests waiting 24 hours after rain/irrigation to avoid crop contamination.

Hmm - wondering if this problem is less of an issue in small home gardens?

The tests were done in commercial spinach fields, but rain is rain. it does make you wonder.

Maybe this hints at the actual mechanism we should focus on, rather than "rain":

"In total, 1492 samples comprising of water, leaf and fecal matter were collected for the analysis."

I've read people saying they drive past commercial fields with workers taking a dump right in the field.
Any home gardeners who do that should not harvest right after rain!

Or, if the fields were recently manured with raw manure, I would hope they would have mentioned that in the paper! But I think there are federal regs about how long you have to compost before applying manure.

Having mulch under leafy crops always sounded smart to me.