“Spoiled squid” causes “hemolytic uremic syndrome” just because it was kept in the refrigerator for 5 days?

Real points:

The cause of the poisoning is still under investigation, but it is more likely that the squid was contaminated before being placed in the refrigerator.

Verifier: Yun Wuxin | Doctor of Food Engineering

A few days ago, there was a news report that an 11-year-old boy in Dongguan developed "hemolytic uremic syndrome" because he ate squid that had been "stored in the refrigerator for 5 days." The child's symptoms were very serious. According to the doctor, there was a 50% chance that he would develop chronic renal failure and would need lifelong dialysis.

Such serious consequences make people very worried: Can eating "expired" or "spoiled" squid really cause kidney failure? How did this happen? And how can we avoid it?

1. What kind of disease is hemolytic uremic syndrome?

Hemolytic uremic syndrome is a syndrome caused by microvascular destruction. Its basic characteristics include hemolytic anemia, thrombocytopenia, acute renal failure, etc.

It is currently believed that Shiga toxin is the main cause of most hemolytic uremic syndrome, among which Escherichia coli O157:H7 is the most common cause. In addition, Shigella dysenteriae, Salmonella, etc. may also be related to hemolytic uremic syndrome.

When people eat food containing Shiga toxin, the toxin is absorbed into the blood and destroys red blood cells, causing microvascular bleeding, hematuria, abdominal pain, vomiting, and then kidney disease, and blood vessels of important organs such as the heart and brain are affected. When the kidneys are severely damaged, long-term dialysis is required.

In addition to this main cause, other factors may also cause HUS, such as bone marrow transplantation, chemotherapy for cancer, diseases that affect the immune system (such as lupus or HIV), certain medications for treating heart disease or clotting disorders, pregnancy, etc.

2. Inadequately cooked meat and raw milk may be contaminated by Shiga toxin-producing E. coli, posing a risk of human infection

Shiga toxins are toxins produced by Shigella dysenteriae, a common bacterial disease that is usually spread among people by the fecal-oral route.

In addition, E. coli is a widely existing bacterium in nature, with many species, and most people can live in peace with humans. But some of them can produce toxins that are very similar in structure to Shiga toxins, also known as Shiga toxins. E. coli O157:H7 is the most important E. coli that can produce Shiga toxins. The main hosts of this type of E. coli are cattle, sheep, deer, etc. In addition, other mammals (such as pigs, horses, rabbits, dogs and cats) and birds (such as chickens and turkeys) can also be infected by this bacteria.

E. coli O157:H7 is mainly transmitted to humans through contaminated food, such as undercooked meat and raw milk, fecal contaminated water, minced meat, air-dried sausage, cheese made from raw milk, etc. In addition, it may also be related to fruits and raw vegetables (such as sprouts, spinach, lettuce, etc.), because these fruits and vegetables are presumably contaminated by contact with livestock or wild animal feces during planting and processing. This bacteria has also been detected in natural water bodies, so swimming in swimming pools or natural waters contaminated by feces also poses a risk of infection.

3. It is unlikely that the squid will go bad after being refrigerated for 5 days. It is more likely that it has been contaminated before being refrigerated.

In this case, the news report only mentioned two things that happened to the boy a few hours apart: "eating squid" and "getting sick", as well as the background information that "the squid had been in the refrigerator for 5 days". Based on this information, the parents and doctors believed that "the squid that had been in the refrigerator for 5 days" was the culprit, and this possibility certainly exists.

However, there are not many bacteria that can cause this symptom, usually the type of Escherichia coli that can produce Shiga toxin. Although they can survive at refrigeration temperatures, they generally cannot proliferate. Common bacteria that can proliferate at refrigeration temperatures, such as Listeria, cannot produce Shiga toxin. In other words, if there are bacteria or toxins that cause hemolytic uremic syndrome in those squids, they should have been there before refrigeration, not caused by "being in the refrigerator for 5 days." In other words, the squid may have been contaminated before being put into the refrigerator.

Of course, there is another possibility, that is, the 11-year-old boy's "hemolytic uremic syndrome" is caused by other reasons mentioned above, which can also explain why the boy's sister who also ate a plate of squid was fine. Of course, since the news report did not mention more details, this is just a guess.

4. How to prevent similar food poisoning incidents

Assuming that the food poisoning was caused by the squid being contaminated by bacteria, there is another very important but easily overlooked point in this incident, which is the processing of the squid. According to news reports, the squid was taken out of the refrigerator and simply fried with peppers. The cooking method of "frying" not only has a short heating time but also is prone to uneven heating. Shiga toxin-producing Escherichia coli can be killed when the temperature of all parts of the food reaches above 70°C, and Shiga toxin is not heat-resistant. Therefore, even if the squid is really contaminated by bacteria, it will not cause food poisoning if it is fully cooked.

Therefore, whether it is contamination by Shiga toxin-producing bacteria or spoilage caused by food being left out for too long, the measures to prevent such incidents are the same as those to prevent other foodborne diseases, namely the "Five Keys to Food Safety" recommended by the World Health Organization:

1. Keep food and kitchen utensils clean

2. Keep raw and cooked food separate during food preparation

3. Heat the food thoroughly and cook it thoroughly

4. Store prepared food at a safe temperature (above 60°C or below 4°C)

5. Use safe water and food ingredients

It should be noted that the refrigeration temperature of the refrigerator (0-4°C) can inhibit the growth of most bacteria, but it cannot kill bacteria. Some bacteria can also proliferate at this temperature. Especially for fresh food, it can only be stored in the refrigerator for a certain period of time. Taking fresh seafood as an example, the FDA recommends that it be stored for 1-2 days.

Editor of this article: zoey