One Less Thing to Worry About: Undercooked Pork

We have plenty of things to worry about: the pandemic, global warming, the economy, racial tensions, and much, much more. But here is some good news to ease the worry burden: you can stop worrying about eating undercooked pork. 

Most people agree that undercooked pork is bad, but not everyone can explain why. The “why” is a nasty little parasitic worm called Trichinella that can cause the disease trichinosis, also called trichinellosis and trichiniasis. Dietary laws in Judaism, Islam, and some other religions prohibit eating pork; this was once thought to be based on health considerations, but that hypothesis has fallen out of favor. The anthropologist Marvin Harris thought the religious prohibitions were a response to ecological and economic factors, rather than to health risks. I’m going to discuss the evidence about the risk of undercooked pork. If you follow religious prohibitions and avoid all pork, you might as well stop reading now.

Trichinella’s life cycle

It usually goes like this: A pig or a human eats meat that contains trichinella cysts. That might happen if pigs eat the carcasses of infected rats or are fed with raw meat garbage, or if humans eat infected pork that is undercooked. Digestion in the stomach releases the trichinella larvae from the cysts, and the larvae travel to the small intestine, where they molt four times over a little more than a month to become adult worms, mate, and produce new larvae. The adults are pooped out of the intestinal exit door and die. The larvae pierce through the intestinal mucosa, enter the lymph and the blood stream, and travel throughout the body. When their final destination is most sites in body, they die; but the lucky ones that end up in skeletal muscle are able to encyst and survive. There they wait for the host to die and for its muscles to be eaten by another animal so the cycle can continue. Can you imagine all those worms and larvae and cysts being inside your body? Are you grossed out yet?

Symptoms, diagnosis, and treatment

If you ingest fewer than 70 larvae, you may have no symptoms and might never know you were  infected. If you ingest 70-150 larvae, you may develop gastrointestinal symptoms a couple of days later, with diarrhea and abdominal pain. In a later parenteral phase, you might develop fever, muscle pain, swelling around the eyes, and a high eosinophil count. Trichinosis is diagnosed by blood tests or muscle biopsy, but both may give false negative results early in the course of the disease. And antibodies can persist for years, so a positive blood test may not indicate a current infection. If you are diagnosed with trichinosis, it’s not the end of the world; treatment with the anti-parasitic drug albendazole is effective if taken early in the course of disease. If it’s too late for albendazole to get the job done, there’s no need for panic; even without treatment, the symptoms will usually resolve on their own within a few months.  Complications of heavy infestations can occur, with myocarditis, encephalitis, meningitis, pneumonia, and even death.  But such outcomes are exceedingly rare.

Incidence in the US has declined drastically

In 1980 Congress passed the Federal Swine Health Protection Act which prohibited feeding swine with trichinella-contaminated food. Other measures have helped, such as inspections, animal testing, rodent control, limiting commercial pigs’ contact with wildlife (free range practices increase risk), improved hygiene, and immediate removal of dead pigs from pens. The incidence remains high in many countries, especially in China, where 10,000 cases of trichinosis are reported every year. But in the United States trichinosis has been eliminated, for all practical purposes. Trichinosis is a reportable disease. The CDC tracks cases and publishes the results of its surveillance activities in the Morbidity and Mortality Weekly Report (MMWR). In the period from 2008 to 2012,  a total of 90 cases were reported, for a mean annual incidence of less than one-tenth of one case per million population. Meats other than pork accounted for more than half of the cases, including meat from bears, deer, and even two that were linked to ground beef (Did you know hamburgers can give you worms?).  Several cases were linked to wild boar and home-raised swine. Many other animals are known to harbor trichinella, including horses, walrus, and many other animals whose meat is not sold in US supermarkets.

In 2008 there was an outbreak of trichinosis in northern California caused by consumption of undercooked bear meat. The attack rate was high: of 38 people attending an event where the bear meat was served, 30 became sick. The bear in question had been shot while lying down and had appeared to be sick. There’s a lesson in that for hunters.

So developing trichinosis from eating undercooked pork is not impossible in the US, but the overall risk is an order of magnitude less than one in a million. And the risk is much less if you avoid eating the meat of wild animals, especially bear meat. Note: freezing pork will kill the trichinella organisms, but freezing bear meat won’t.

What degree of risk is reasonable?

A micromort is a unit of risk defined as a one-in-a-million chance of death; a microprobability is a one-in-a-million chance of some event. Most people are willing to accept a one-in-a-million risk. Skiing incurs a risk of 0.7 micromorts per day; running a marathon carries a risk of 7 micromorts per run; hang gliding, 8 micromorts per trip; scuba diving, 5 micromorts per dive; giving birth, 120 micromorts; and travelling increases the risk by one micromort when you travel 1000 miles by jet, 230 miles by car, 10 miles by bicycle, or even 17 miles by walking. 

In comparison, the risk of dying from eating undercooked commercial pork products in the US is far less than one micromort, and the risk of developing trichinosis is well below one microprobability. 

Current cooking guidelines

Recommendations for cooking pork have been revised. Official guidelines no longer require us to cook all pork to 160 degrees. Now they say it is sufficient to cook common cuts of pork to an internal temperature of 145 degrees Fahrenheit followed by a 3-minute rest (the reason for the rest is that the temperature continues to rise for a short time after removal from the heat source). The resulting product will be pinker than most home cooks are used to.  160 degrees is still recommended for all ground meats.

“It’s great news that home cooks can now feel confident to enjoy medium-rare pork, like they do with other meats,” said Guy Fieri, a chef, restaurateur and host of several food-focused television programs. “Pork cooked to this temperature will be juicy and tender. The foodservice industry has been following this pork cooking standard for nearly 10 years.”

The bottom line

There’s a long list of things that I might legitimately worry about (not that worry ever did any good!), but I have taken undercooked pork off my list. I no longer worry if I detect a tinge of pink in my pork chop. Guy Fieri is right: pork does taste better when it is medium-rare. It’s a relief to have one less thing to worry about, and I enjoy my meals more. You can too. Relax! Bon appétit!

This article was originally published as a SkepDoc’s Corner column on the  CSI website

Dr. Hall is a contributing editor to both Skeptic magazine and the Skeptical Inquirer. She is a weekly contributor to the Science-Based Medicine Blog and is one of its editors. She has also contributed to Quackwatch and to a number of other respected journals and publications. She is the author of Women Aren’t Supposed to Fly: The Memoirs of a Female Flight Surgeon and co-author of the textbook, Consumer Health: A Guide to Intelligent Decisions.

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