And salad too -- more recalls

Big day for recalls, just before the Fourth of July.  This time it's sprouts, lettuce, and sprouts.  Here are the details:

Banner Mountain Sprouts in California is voluntarily recalling some of its organic products because of possible contamination with salmonella.

Dole Fresh Vegetables is recalling about a thousand bags of bagged greens for possible contamination with Listeria monocytogenes.   The salads were distributed in six U.S. states (Georgia, Kentucky, North Carolina, South Carolina, Tennessee and Virginia).

Leasa Industries Co., Inc., is recalling alfalfa sprouts because of possible contamination with salmonella.  While the recall notice does not quite specifically say so, this recall seems to be limited to Florida.

So that's two salmonellas and a Listeria all in green leafy things.  I know sprouts are grown in conditions ideal for pathogen growth, but how does the Salmonella get in there in the first place?  Salmonella "are microscopic living creatures that pass from the feces of people or animals to other people or other animals," according to the USDA.  So again, my questoin, how does Salmonella get from the feces to the sprouts in the first place?  This simply should not be happening.