Is Shrimp Safe?

Did you know that eating just a single shrimp could potentially exceed the safety limit for banned pesticides and chemicals. Here’s our first story.

Over a decade ago, farmed shrimp overtook wild-caught, such that by 2016, two-thirds of global shrimp production was farmed. The main potential food safety hazards of shrimp farming are infectious disease, chemical contamination, and veterinary drug residues.

In terms of mercury, shrimp is the second leading source, but it’s still far behind tuna. In terms of banned pesticides, flame retardants, and polycyclic aromatic hydrocarbons, there are some significant concerns regarding human health risks associated with shrimp consumption. Safety limits were exceeded for banned pesticides chlordane, DDT, heptachlor, aldrin, Dieldrin, and endosulfan. Now, this was based on worst case scenario values, but on the other hand, based on just eating three and a half grams of shrimp a day, which is like a single shrimp, or one serving of shrimp every two weeks or so. Eating just one shrimp could give you as much as 50 times more DDT than is considered safe. Same with flame retardant chemicals, and same with naphthalene and benzopyrene.

For PFAS forever chemicals, eating the highest levels of the most contaminated shrimp could pose a health risk, which comes out to be about a serving a day. Shrimp can also be a substantial source of carcinogenic heterocyclic amines, which is typically seen in dry-heat cooked chicken, like baked, grilled, fried, or broiled. Levels for shrimp were in the 10 to 50 range, which is what you start to see with chicken grilled at over 400 degrees Fahrenheit (200+ °C). Note that steaming, or presumably boiling or other moist cooking methods, are the safest ways to cook meat.

Another issue with shrimp is foodborne illness––even with precooked ready-to-eat shrimp, which have been found to be an international vehicle of antibiotic-resistant bacteria. As shrimp farming has gotten more intensive, there is an increased occurrence of disease problems as a direct result of the higher stocking densities at shrimp farms, causing stress-initiated disease and rapid transmission of infectious diseases, and along with more disease, comes more use of antibiotics and disinfectant chemicals to keep the animals from dying prematurely.

In India, where most of the shrimp eaten in the United States comes from, 90% of the bacteria tested were resistant to three or more classes of antibiotics. Thus, shrimp could serve as delivery vehicles of antimicrobial resistance to pathogenic bacteria to consumers and from country to country. Thirteen brands of ready-to-eat shrimp from four countries of origin were obtained from local grocery stores in the U.S., and 80% of the bacterial species picked up were antibiotic-resistant. And that included numerous resistant human pathogens, such as E. coli and Salmonella. Foodborn pathogens were found in every single sample tested. And most of those contained multiple pathogens. Ready-to-eat shrimp are sold with instructions to just thaw before serving, which may also result in consumer exposure to antibiotic-resistant bacteria.

Enterococci are used as markers of fecal contamination of food products. At a retail level, about 85% of ground beef and turkey are contaminated with fecal bacteria, and about half of chicken and a third of pork. Sampling more than 700 shrimp at grocery outlets in eight states across the United States, researchers found that approximately two-thirds of the shrimp samples were contaminated with fecal bacteria.

And in terms of antimicrobial resistance in U.S. retail seafood, shrimp had the highest odds of being contaminated. And the risk was about twice as high in farm-raised shrimp compared to wild-caught shrimp. A small percentage were even resistant to a carbapenem antibiotic, which is considered the antibiotic of last resort. In the hospital, we used to call it gorillacillin. It’s also been found in Canadian shrimp, linked to a farming operation in India, our #1 source of shrimp imports. And others traced back to Vietnam and Ecuador, other major shrimp importers into the United States. So, shrimp farms may be a key reservoir of antibiotic-resistant genes, which may pose a significant threat to public health. When we consume shrimp, we may also be consuming those antibiotic resistance genes, which can be passed along to human pathogens in our own body. Resistance genes have been detected in shrimp products destined for human consumption. But what about the antibiotics themselves? Are there residues of antibiotic drugs left in shrimp at a retail level? That’s what I’ll cover, next.

Next, we look at the high level of drug residue in imported shrimp.

About 90% of shrimp consumed in the United States is imported, and because much imported seafood is farm-raised in confined conditions, drugs are used to prevent or treat disease and increase survival rates, and residues of some of these drugs can cause cancer or allergic reactions, or contribute to antibiotic resistance.

Among different kinds of seafood, shrimp have had the highest frequency of veterinary drug violations, primarily for nitrofurans and chloramphenicol. The United States banned chloramphenicol 35 years ago due to a link with a rare and often fatal disease called aplastic anemia. Nitrofurans are also dangerous because of their potential cancer-causing properties. So, their use in animals produced for human consumption is similarly banned in Europe and the United States.

For something as potentially dangerous as chloramphenicol, governments around the world have established zero-tolerance policies, which means that no residues in food are permissible. However, traces of chloramphenicol have been detected in shrimp. Unlike most of the animals we eat, who have multiple organs for drug excretion, shrimp possess only one, which may allow more antibiotics to build up in them. But you don’t know, until you put it to the test.

There have been four studies published on the presence of banned drugs in retail U.S. shrimp. One found that 92% of imported, farm-raised shrimp tested positive for at least one drug that is banned for use in the United States. Another, of just six shrimp from stores in Arizona and California, found drugs in two of them. The third tested dozens purchased in Louisiana from many of our main shrimp importers, and 70% tested positive for the zero-tolerance carcinogenic nitrofurantoin. Of all the countries, Vietnam appeared to be sending us shrimp with the most types of antibiotic residues. The 100% positives in Bangladesh and Ecuador were based on just a single positive sample—one out of one—for both countries. The fourth, however, found no antibiotic residues. Unfortunately, only a small fraction of imports are tested by the U.S. Food and Drug Administration, and therefore the potential for shipments with antibiotic-tainted shrimp to slip through the cracks remains.

And they’re mostly from Asia, which has been identified as posing a very significant risk to the global burden of antibiotic resistance. Stocking densities on shrimp farms are often very high, which concentrates bacteria and raises stress levels in the animals, which increases their susceptibility to infection, leading to outbreaks that kill like a billion shrimp at a time. Shrimp don’t respond to vaccination; so, to combat disease, farmers employ a range of chemicals––the residues of which can end up in the final product we may eat.

Even in more traditional systems, where human and animal waste is dumped into shrimp ponds, the antibiotics that end up in the manure end up just increasing overall antibiotic exposure. Aside from the potential for fostering antibiotic resistance, consuming antibiotic residues can have a direct toxic effect, and the constant traces of antibiotics can also disrupt the human microbiome, as has been demonstrated. The consumption of shrimp containing potentially unsafe levels of antibiotics from aquaculture, shrimp farming, is a global concern due to overuse of antibiotics. There is clearly an urgent need for governments to regulate the use of antibiotics in crustacean production.

In 2001, chloramphenicol was detected in shrimp imported into Europe from Asia, triggering a food scandal, and the regulatory response spilled over to other major seafood-importing countries, including the United States. The U.S. Food and Drug Administration started testing, and every year has rejected shrimp due to the presence of antimicrobial drugs––the most contaminated of all tested seafood products. That shows the system is working, right? Well, only a small amount of imported seafood is actually inspected. How small? For shrimp, about four samples out of every 10 million pounds (4,535 tons) of shrimp are tested. So, assuming there are about 25 shrimp in a pound (0.45 kg), that’s like one sample tested for every 60 million shrimp. Of course, they come in big batches, yet the FDA only tests about 0.1% of the million annual shipments that come in every year. Based on this level of testing, seafood shipments from a foreign processing facility would have a roughly one in a thousand chance of being selected by the FDA for drug residue testing. Is that because positive findings are so rare? No, about every one in every 10 shipments of shrimp turns up contaminated with unsafe drug residues. So, that means like a hundred shipments of the other 999 that weren’t tested may also be contaminated; yet, they can go straight to restaurants or grocery stores.

And we only test for a few drugs. Europe, Japan, and Canada are picking up seven to 10 different drugs, whereas we only look for two. So, we are likely missing the wider range of drugs picked up by other countries.

Why doesn’t the FDA test more? According to FDA officials, they don’t have the resources to test more. Okay, said the GAO (Government Accounting Office), which is the congressional watchdog, how about forcing the countries that are sending the shrimp to test for drugs before they ship them here? Let them pay for it. That’s what Europe does. Well, the FDA decided not to pursue such agreements with other countries to require them to test seafood exported to the United States for unsafe drug residues, as Europe does. Why not?

They didn’t think some of the countries that send us shrimp might be able to, because they lack the laboratory infrastructure and capabilities needed to test for the drugs of concern to the FDA. I’m reminded of an outbreak investigation of salmonella linked to shrimp, where the investigators had to explain to the exporters that they probably shouldn’t be scooping up shrimp off the floor.

But wait, countries exporting to Europe are able to comply; so, what ends up happening is that the United States may still be a market for at least some seafood that did not meet the safety standards of Europe. As a result, shrimp that cannot be shipped to European countries because of concerns about violative drug residues may be shipped to the United States: no problem. It’s like the use of some coloring agents used to disguise shrimp diseases: approved in the United States, but prohibited elsewhere due to concerns around causing ADHD symptoms in children. Countries know they can always send products here, and even if they do use drugs they aren’t supposed to, there’s only a one in a thousand chance we’ll even check.

In our last story, we look at how asymptomatic food sensitivities to foods like shrimp may increase the risk of premature death for those who eat them.

When people were randomized to consume shellfish or the same weight of protein of meat, cheese, and eggs, surprisingly shrimp did not lower their LDL cholesterol––perhaps because shrimp is so high in dietary cholesterol. Shrimp is exceedingly low in saturated fat, like 30 times less than other meat. But it has about twice as much cholesterol, which dietary guidelines recommend we reduce in our diet to as low as possible. If people are given the same amount of cholesterol in the form of shrimp or eggs, they get about the same rise in LDL cholesterol, which alone could increase our lifetime risk of heart disease by about 15%. But there are a lot more people eating two eggs a day than like 11 ounces (310 g) of shrimp a day. And eating wild-caught cold-water prawns, a different species of shrimp, doesn’t appear to budge LDL cholesterol much at all. Unfortunately, about one in three shrimp in the grocery store is mislabeled; so, it may be hard to pick and choose.

There is another way meat may contribute to heart disease risk. In certain areas of the United States and around the world, getting bitten by certain types of ticks can make you allergic to meat. In some parts of the U.S. where the lone star tick is endemic, as many as 20% of people have allergy-type antibodies against meat in their bloodstream. But the prevalence of clinically appreciated allergic symptoms is thought to be at least 10-fold less. So, they’re sensitized to meat, but when they eat it, they don’t exhibit any symptoms. And because of that, they continue to eat meat. But what if that’s causing inflammation inside their bodies, even if they don’t feel it? And most concerningly, what if it’s causing more inflammation in their artery walls? Indeed, there were significantly greater amounts of atherosclerotic plaque in the individuals who had detectable levels of the anti-meat allergy antibodies in their system. So, people who consume mammalian meat appear to have this chronic inflammation in the walls of their coronary arteries that relates to this interaction between this alpha-gal component of meat and their anti-alpha-gal antibodies, if they’ve been bitten by a tick.

Those having a heart attack had about a whopping 13 times higher likelihood to having those antibodies, providing strong supportive evidence for a clinically important effect of alpha-gal sensitization on the development of coronary heart disease, our leading cause of death, and acute myocardial infarction, or heart attack. Okay, but wait a second. If having an asymptomatic food allergy can so inflame our arteries, what about other food allergies?

An allergy to shrimp is actually the most common food allergy in the United States, affecting up to 1 in 50 Americans. But those are the people who experience symptoms. Might a shrimp allergy actually be affecting more? People with symptomatic seafood allergies tend to know they are allergic, and know to just stay away from shrimp. But some people with shrimp allergies react differently. Some have classic allergy symptoms like breaking out in hives, swelling, and difficulty breathing, but others develop symptoms that manifest hours later—gastrointestinal symptoms like nausea, abdominal cramps, diarrhea, and vomiting. So, some shrimp-sensitive patients just have this kind of gastrointestinal upset. But what about people who are sensitized to shrimp, and they don’t even know it because they don’t exhibit any symptoms?

In individuals without symptomatic food allergy, having allergy antibodies in their blood targeting some food was considered clinically irrelevant. But that was before those tick-induced meat sensitization studies came out. So, researchers looked to see if having allergy antibodies against foods was associated with cardiovascular mortality, and, indeed, that’s just what they found. From blood tests, it appears about one in 25 people is allergic to milk, whether they know it or not. And in these two large studies, those who had the milk sensitivity had between two and nearly four times the risk of dying from cardiovascular disease, but the worst appeared to be shrimp. Six percent of Americans, about one in 17, have anti-shrimp antibodies in their blood, whether they know it or not, and those who do are 3.7 times more likely to die of cardiovascular disease––but only if they eat shrimp. Having anti-shrimp antibodies doesn’t matter if you don’t eat shrimp.

What about having a milk, peanut, or egg sensitivity, but not eating those foods? There were too few people not eating those foods to actually calculate it, but enough people don’t eat shrimp that researchers could see that having anti-shrimp antibodies only mattered if you kept eating shrimp. The thought is that chronic oral exposure to foods we have hidden allergy antibodies for can lead to chronic inflammation that can manifest in our arteries. This definitely challenges the current thinking that these kinds of food sensitivities without overt allergy is benign.