Seafood when traveling

Seafood is one of the pleasures of travel, and most of it is safe when it is fresh, cooked all the way through and served hot. The risks sit in two places. Raw or lightly cooked seafood (oysters, sushi, ceviche) can carry bacteria, viruses and parasites that cooking would have killed. And a few poisonings come from toxins that cooking does not touch: red tide in shellfish, ciguatera in reef fish, and scombroid in fish that was not kept cold. For those, what you order and where it came from matter more than how it is cooked.

This guide explains each risk, how to order with less of it, who should be stricter, and the symptoms that need a doctor fast. The everyday rules for food and water are in our guide to avoiding food poisoning when traveling.

Cooked or raw: what cooking fixes and what it doesn’t

Risk	Typical seafood	Killed by cooking?
Vibrio bacteria	Raw or undercooked shellfish, especially oysters	Yes
Norovirus, hepatitis A	Raw or lightly steamed oysters and other shellfish	Yes, if cooked thoroughly, not just steamed open
Anisakis worms	Raw or undercooked fish and squid	Yes (freezing also works)
Shellfish poisoning (red tide)	Mussels, clams, oysters, scallops, also some crabs, shrimp and lobster	No
Ciguatera	Large tropical reef fish	No
Scombroid (histamine)	Tuna, mackerel, mahi-mahi, sardines, anchovies, marlin	No

The CDC is clear on the last three: the toxins are not destroyed by cooking, freezing, canning, salting, smoking or pickling. Fish with ciguatera looks, smells and tastes normal. Fish with scombroid usually does too, but it can taste peppery, sharp or salty.

Is it safe to eat raw oysters abroad?

Raw oysters carry risk anywhere, including at home. Oysters filter seawater to feed, so the Vibrio bacteria that live naturally in coastal waters can build up in them. The CDC says most people with vibriosis get it from raw or undercooked shellfish, especially oysters. Most cases mean diarrhea and vomiting, but Vibrio vulnificus can cause a life-threatening infection: about 1 in 5 people with it die, sometimes within a day or two.

Some myths are worth dropping:

• You cannot spot a bad oyster. A contaminated oyster looks, smells and tastes the same as a safe one (CDC).
• Hot sauce, lemon juice and alcohol do not kill Vibrio. Only cooking does (CDC).
• Winter is not a free pass. Infections peak in warm months, but the CDC reports them year-round.

Oysters can also carry norovirus and hepatitis A, picked up from polluted harvest water or a sick food handler. The CDC says quick steaming does not heat shellfish enough to kill norovirus: shellfish should be cooked thoroughly, not just steamed open. The WHO notes that hepatitis A typically spreads through raw or undercooked seafood, and that raw or undercooked seafood has been implicated in cholera outbreaks.

Where food and water controls may not be adequate, TravelHealthPro, the UK’s travel health service, advises avoiding shellfish altogether, because it can be contaminated with bacteria and viruses as well as toxins. The CDC’s travel advice says the same: ideally, travelers to developing countries should avoid eating shellfish. A hepatitis A vaccine protects against one of these risks; a travel clinic can tell you whether you need it.

Is sushi safe when traveling? Raw fish and ceviche

Raw fish can carry the larvae of Anisakis, a roundworm found in sea fish and squid. The CDC says anisakiasis is most common where raw fish is popular, such as Japan, and has also been reported in the US, Europe and South America. It can cause stomach pain, nausea, vomiting and diarrhea, and some people have an allergic reaction, rarely a severe one (anaphylaxis).

Freezing kills these parasites. The CDC gives the FDA’s options, for example freezing at -20°C or colder for 7 days, or at -35°C until solid and then for 15 hours. But the FDA adds that freezing kills some parasites, not all harmful germs: cooking is the safest choice.

Ceviche, kinilaw and other dishes “cooked” in lime juice or vinegar are still raw. The acid changes how the fish looks, not what it carries. In Thailand, raw fish, crab and prawns go into several traditional dishes: see raw and fermented dishes in Thailand.

If you eat raw fish:

• Choose a restaurant where the fish is kept on ice or in a chilled display.
• Skip it on a hot day at a stall without refrigeration.
• If you belong to a higher-risk group (see below), choose cooked fish, cooked shellfish or vegetable rolls.

Red tide and shellfish poisoning

A red tide is a bloom of algae that produce toxins. Shellfish that filter the water concentrate them. According to the CDC, the toxins can be found in mussels, oysters, clams, scallops, cockles, abalone, whelks and moon snails, and also in some crabs, shrimp and lobster. The name can mislead: TravelHealthPro notes that blooms may be called “red tides” or “brown tides”.

The most serious form, paralytic shellfish poisoning, starts with numbness and tingling of the mouth, face and limbs, usually 30 to 60 minutes after eating. In severe cases it causes paralysis and stops breathing. The CDC Yellow Book says the risk of death depends on access to modern care, including a breathing machine, and can be particularly high in children. Other forms cause vomiting and diarrhea within a few hours, or, more rarely, confusion and memory loss.

What to do:

• Follow local warnings. TravelHealthPro advises paying attention to any posted warning about algal blooms. Don’t eat shellfish you collected yourself from a beach without checking first.
• Don’t count on cooking. A warning means the shellfish are unsafe whether raw, boiled or grilled.
• Ask where the shellfish came from if you are near an area with a warning.

In some countries this is a regular, official topic. In the Philippines, for example, the fisheries bureau publishes shellfish bulletins listing the coastal areas where shellfish are unsafe.

Ciguatera: when reef fish make you sick

Ciguatera comes from toxins made by tiny algae on coral reefs. Small fish eat the algae, bigger fish eat the small fish, and the toxin builds up as it moves up the food chain. The CDC says it is particularly common in the Pacific and Indian Oceans and the Caribbean, and newer risk areas include Madeira and the Canary Islands.

The fish most often involved are large reef predators: barracuda, moray eel, grouper, amberjack and sea bass, and also parrotfish and red snapper. The CDC’s advice to travelers:

• never eat barracuda or moray eel;
• avoid reef fish, particularly those heavier than about 2.3 kg (5 pounds);
• don’t eat the liver, intestines, roe (eggs) or head of reef fish, where the toxin is most concentrated.

Germany’s Federal Institute for Risk Assessment (BfR) is stricter: for travelers, it says the safest way to avoid ciguatera is not to eat sea fish and seafood in risk areas at all, especially fish you caught yourself. If you want no risk, follow that advice.

Symptoms usually start 3 to 6 hours after the meal, sometimes up to 30 hours later: nausea, vomiting, diarrhea and stomach pain, then tingling, tooth pain or a feeling that the teeth are loose, itching, a metallic taste, and a strange reversal of hot and cold (cold water feels burning). Most people recover in a few days, but nerve symptoms can last weeks, and sometimes months or even years. There is no cure, only treatment of the symptoms. After ciguatera, the CDC advises avoiding fish, nuts, alcohol and caffeine for at least 6 months, as they can bring symptoms back.

Because symptoms can start late, they may begin on the flight home. Tell the doctor that you ate reef fish on your trip.

Scombroid: the “allergy” from badly stored fish

Scombroid is one of the most common fish poisonings, and it happens all over the world. When fish such as tuna, mackerel, mahi-mahi, sardines, anchovies, herring, bluefish, amberjack or marlin are not chilled quickly after being caught, bacteria turn a natural substance in the flesh into histamine. The CDC says this happens fastest at 20 to 30°C, which is why fish needs to stay iced from the boat to the kitchen.

It looks like an allergic reaction and starts fast, usually within minutes to an hour: a red, flushed face that looks like sunburn, headache, itching, a racing heart, cramps, diarrhea and blurred vision. The fish may taste peppery, sharp or salty, but often tastes normal. Cooking, smoking or freezing does not help. Antihistamines usually relieve it, and people generally recover within 12 to 48 hours.

Scombroid is easily mistaken for a fish allergy, and the reverse is also true. If you have a known fish or shellfish allergy, or if you have trouble breathing, swelling of the lips or throat, or feel faint, treat it as an allergic emergency: our guide to eating out abroad with a food allergy gives the signs of anaphylaxis, what to do, and how to order safely.

Pufferfish: avoid it entirely

Pufferfish (fugu) contains tetrodotoxin, a poison with no antidote that can paralyze breathing. The CDC advises travelers to avoid it and other potentially toxic fish “even when prepared by trained chefs in licensed restaurants.” TravelHealthPro gives the same advice.

How to choose and order seafood

• Cooked through, served hot. Fish should be opaque and flake easily. Shrimp, scallops, crab and lobster should be firm, pearly and opaque. Mussels, clams and oysters should be open: the FDA says to throw away any that stay closed.
• Kept cold. Fish should be in a fridge or on a thick bed of fresh ice. The FDA says not to leave seafood out for more than 2 hours, or 1 hour above 32°C. Grilled fish from a beach stall is a better bet when you see it come out of an iced box.
• Fresh signs at a market or a display. The FDA lists a mild smell, clear and shiny eyes, firm flesh and red gills for whole fish. Throw away shellfish with cracked shells; live clams, oysters and mussels close when tapped. These signs help with spoilage, but no look or smell test can show red tide toxins, ciguatera or Vibrio.
• Ask what it is. The name of a “catch of the day” can hide a large reef fish. Ask the species and, in reef areas, how big it was.
• Mind the parts. Skip the liver, roe and head of reef fish.
• Watch for warnings. Red tide notices, closed beaches and local advice on which fish not to eat.

If you have an open cut, tattoo or recent piercing, the CDC advises keeping it out of seawater and away from raw seafood and its juices, or covering it with a waterproof dressing: Vibrio can also infect wounds.

Who should be stricter

• Liver disease, diabetes, cancer, HIV, thalassemia, a weak immune system or medicines that suppress immunity: the CDC says these raise the risk of a severe Vibrio infection. Don’t eat raw oysters or other raw shellfish.
• Medicines that reduce stomach acid, or recent stomach surgery: the CDC and TravelHealthPro list these as raising the risk of infection.
• Pregnant travelers, young children and older people: the FDA advises them to avoid raw or undercooked fish and shellfish, including sushi, sashimi, ceviche and raw oysters. Pregnancy also brings advice on smoked fish and high-mercury fish: see our guide to eating abroad while pregnant.
• Children and shellfish poisoning: the CDC Yellow Book notes that deaths from paralytic shellfish poisoning can be particularly high in children.
• Asthma: one kind of shellfish poisoning (neurotoxic) can also be breathed in from sea spray during a bloom, and the CDC says people with asthma may be more affected.

Symptoms after eating seafood: when to get help

The CDC advises seeking medical care immediately if you think you have seafood poisoning while traveling. Get help as an emergency (call the local emergency number) for:

• numbness or tingling of the lips, mouth or face, weakness, trouble swallowing or trouble breathing after eating shellfish or fish;
• swelling of the lips or throat, wheezing, or feeling faint;
• after eating raw shellfish, or after a wound has been in seawater: fever and chills with very low blood pressure, blistering skin, or a wound that turns red, swollen, hot and painful. The CDC says these need care right away.

See a doctor soon for:

• flushing, headache and a racing heart soon after a fish meal (possible scombroid);
• tingling, a reversal of hot and cold, or itching hours after eating reef fish (possible ciguatera), even after you are home;
• stomach pain, vomiting or blood in the stool after raw fish or squid (possible anisakiasis).

For ordinary vomiting and diarrhea, drink plenty of fluids, ideally oral rehydration solution, and follow our guide to food poisoning while traveling, which gives the thresholds for seeing a doctor and how to find one abroad. If you can, tell the doctor what you ate, when, and where it came from.

What to pack

• Oral rehydration salts.
• Antihistamines, after checking with a pharmacist that they suit you: the CDC says they usually relieve scombroid.
• If you have a fish or shellfish allergy: your adrenaline auto-injectors and an allergy card in the local language (see the allergy guide above).
• Travel insurance that covers emergency care and evacuation, especially if you are going to remote islands where paralytic shellfish poisoning or a severe allergy would need a hospital fast.