Most major U.S. grocery chains do a poor job of alerting shoppers about food recalls, a consumer advocacy group warns.

Each year, federal health officials estimate, roughly one in six people gets sick from what we eat. And from frozen beef tainted with salmonella to E. coli in flour, consumers have gotten sick from products later pulled from store shelves, according to U.S. PIRG. While most of those roughly 48 million Americans quickly recover, 128,000 are hospitalized and about 3,000 die, data from the U.S. Centers for Disease Control and Prevention show.

The U.S. food safety system focuses on getting recalled food off store shelves quickly through a "well-defined process followed by regulatory agencies, manufacturers and retailers," PIRG wrote in its report. But consumers are often unaware of a food recall unless they arrange to receive alerts or they hear about a recall through media coverage.

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Retailers also often don't properly explain why an item has been removed from store shelves, PIRG's Adam Garber said. "They don't say, 'Don't eat your lettuce' — they say 'We're out,' rather than it might have E.coli," he told CBS MoneyWatch. "If they have a sign saying, 'We're out of this right now, but we hope to have it back in stock soon,' it doesn't tell you that something in your home might be dangerous."

4 chains pass test

In its report, PIRG graded grocers on how well they warn customers about potentially contaminated products. Over time, that's included products recalled for myriad reasons, from containing undeclared allergens to pieces of plastic.

In gauging each chain's attempts at notifying the public, PIRG looked at the clarity of store policies and whether customers were notified, either by in-store signage or directly via the phone or email. Just four of 26 retailers drew a passing grade of "C" from the group: Target, Kroger, Smith's Food and Drug and Harris Teeter (the latter two of which are owned by Kroger). The others, including Target competitor Walmart, didn't pass muster, the watchdog found.

Walmart did not return a request for comment.

More than three-quarters, or 84%, of grocery store chains fail to offer any public description of their process for notifying customers about recalls, PIRG found. More than half, or 58%, of the chains surveyed by PIRG reported a program to notify consumers.

None of the chains had any information online about where customers could find recall notices in stores. "Customers shouldn't have to go on a scavenger hunt to find out if food they recently purchased was recalled," PIRG stated.