How safe is your shrimp?

The majority of raw shrimp contains some type of bacteria. (iStock)

Americans love shrimp.

Each of us eats, on average, almost four pounds per year, making shrimp more popular than tuna. Once considered a special-occasion treat, shrimp has become so ubiquitous that we now expect to find it on the menu whether we’re at a pricey restaurant or a fast-food joint.

In fact, Americans eat about three times more shrimp than we did 35 years ago. To satisfy our insatiable appetite, the U.S. has become a massive importer: About 94 percent of our shrimp supply comes from abroad, from countries such as India, Indonesia, and Thailand.

But our love affair with shrimp does have a downside. Most of the shrimp we import is “farmed”—grown in huge industrial tanks or shallow, man-made ponds that can stretch for acres.

"Even though most bacteria on shrimp would be killed during the cooking process, our test results raise real questions about how shrimp is raised, processed, and regulated."

— Urvashi Rangan, Consumer Reports Food Safety and Sustainability Center

In some cases 150 shrimp can occupy a single square meter (roughly the size of a 60-inch flat-screen television) where they’re fed commercial pellets, sometimes containing antibiotics to ward off disease. If ponds aren’t carefully managed, a sludge of fecal matter, chemicals, and excess food can build up and decay. Wastewater can be periodically discharged into nearby waterways.

“Bacteria and algae can begin to grow and disease can set in, prompting farmers to use drugs and other chemicals that can remain on the shrimp and seep into the surrounding environment,” says Urvashi Rangan, Ph.D., executive director of the Consumer Reports Food Safety and Sustainability Center. Those shrimp-farming practices raise a variety of concerns—not just about how safe shrimp are to eat but also about the environmental damage that can be caused by farming them that way.

For shoppers the dilemma starts at the grocery store, where it’s difficult to know what to buy.

Labels and names can be confusing, meaningless, or—worse—deceptive. Sellers may not always tell (or even know) the truth about the origins of the shrimp they offer. And the allure of a label proclaiming that shrimp are “natural” or “wild” can obscure the fact that some expensive varieties aren’t necessarily fresher or more flavorful.

That’s why Consumer Reports decided to take an in-depth look at shrimp from a testing, tasting, and shopping viewpoint. We unearthed some worrisome findings, including bacteria on more than half the raw samples we tested and illegal anti­biotic residues on 11 samples. But there was also good news, in that there are plenty of healthful choices available.

Despite America’s massive intake of shrimp, the Food and Drug Administration tested only 0.7 percent of foreign shrimp shipments last year. To do our own testing, Consumer Reports bought 342 packages of frozen shrimp—284 raw and 58 cooked samples—at large chain supermarkets, big-box stores, and “natural” food stores in 27 cities across the U.S. (We didn’t include fresh, never-frozen shrimp because they account for only a small percentage of the shrimp that consumers buy.)

We tested for bacteria such as salmonella, vibrio, staphylococcus aureus, and E. coli. We also looked for drug residues to see whether antibiotics were used in raising the shrimp. Antibiotics—none of which are approved by the U.S. for shrimp farming and which are illegal in imported shrimp—are problematic because their use can ultimately lead to bacteria becoming antibiotic-resistant, meaning that at some point the antibiotic may no longer work to treat common human ailments.

Our findings provided some cause for concern. In 16 percent of cooked, ready-to-eat shrimp, we found several bacteria, including vibrio and E. coli. Those bacteria can potentially cause illnesses such as food poisoning—which could include diarrhea and dehydration—and, in rare instances, can even prove fatal. In 11 samples of raw imported farmed shrimp, we detected anti­biotics. And in seven raw shrimp samples (six farmed and one wild), we found MRSA—methicillin-resistant staphylococcus aureus, a bacteria that can cause infections that are often difficult to treat.

Overall, 60 percent of our raw shrimp tested positive for bacteria, but it’s important to keep those findings in perspective. By comparison, in 2013, when we tested raw chicken breasts, 97 percent of the samples contained bacteria, says Rangan, who oversaw both the shrimp and chicken studies.

Compared with the chicken samples, far fewer shrimp contained salmonella, which is often responsible for outbreaks of food poisoning.

But of concern, we found vibrio on many shrimp samples. “Vibrio is the most common cause of food poisoning from eating raw oysters,” Rangan says. “And even though most bacteria on shrimp would be killed during the cooking process, our test results raise real questions about how shrimp is raised, processed, and regulated.”

Dirty shrimp: What we found

Consumer Reports tested 284 samples of raw shrimp purchased at stores around the country and tested them for bacterial contamination. The last column shows the percentage of samples that contained at least one of the following bacteria: vibrio, staphylococcus aureus, E. coli, listeria, or salmonella—bacteria that can potentially make you sick. Our experts say more should be done to prevent contamination, but note that cooking should kill the bacteria.

So which farmed shrimp should you buy?

Consumer Reports recommends buying farmed shrimp raised without chemicals, including antibiotics. That can include shrimp farmed in large outdoor ponds that mimic the natural habitat or in tanks that constantly filter and recycle water and waste. One reason farmed shrimp is so popular is that it can be cheaper than wild shrimp, which is caught in the ocean. Our tests suggest that wild shrimp from U.S. waters may be worth the higher price. Of all the shrimp we tested, they were among the least likely to harbor any kind of bacteria or contain chemicals.

Still, when it comes to safety and sustainability, responsibly caught U.S. wild shrimp is our top choice. Consumer Reports recommends buying wild shrimp certified by the Marine Stewardship Council, an organization that ensures shrimpers are fishing responsibly; shrimp from Whole Foods Market; and those listed as “Best Choices” or “Good Alternatives” on Monterey Bay Aquarium’s Seafood Watch Guide, at seafoodwatch.org. Read more about the shrimp labels you can trust.

This article also appeared in the June 2015 issue of Consumer Reports magazine.