Welcome to the site, probably there is nothing on this as nobody has suffered a problem, I don’t know except that like you I have been growing leaves in surface composted soil and there have been no health problems, quite the opposite with people loving the leaves so much, and I eat loads.
I have a feeling that there is misunderstanding about bacteria in soil, which is stuffed full of them when healthy – as we are too – and your composted hen manure should be full of beneficial microorganisms.