Why Hasn’t a Vaccine Stopped Salmonella?
By: Sam Westreich
Tags: Medicine, Vaccines, Science, Health, Farming

During college, I spent several weeks binge-watching the show Good Eats, hosted by Alton Brown. The show helped me learn many of the basics of cooking, including valuable lessons like mixing dry ingredients before adding wet ones, the importance of salting food — and being very, very careful with raw chicken.

Raw chicken is often contaminated with a nasty bacterium called Salmonella, whose full name is Salmonella enterica. This bacterium gets many people sick each year — an estimated 1.35 million infections happen in the United States each year, with an estimated 420 deaths per year.

Salmonella’s influence in our kitchens goes beyond raw chicken — it’s also the reason why U.S. eggs need to be refrigerated. In order to minimize the spread of the virus, we wash our eggs in the States, which scrubs off the outer layer and makes them more vulnerable to bacterial growth.

But why do we treat chickens differently in the U.S. than in Europe? Why do U.S. producers need to clean their eggs, while European egg producers don’t?

Let’s find out a bit more about salmonella, chicken sanitation, and why our U.S. eggs need to stay in a fridge.

How Salmonella Makes Us Sick

Most of the time, when we accidentally ingest bacteria, our stomach acid keeps us safe. The powerful acid dissolves the membrane of the bacteria, popping them before they can reach our intestine and cross over into our body.

Salmonella, however, is able to survive the dip in the stomach acid. It makes it to our small intestine, where it produces toxins and crosses the barrier that protects our body from our intestine’s contents. Those toxins lead to an immune response, which can lead to ulcers, diarrhea, and more serious conditions if the bacteria are able to gain a foothold outside the intestine.

Most of us won’t die from a salmonella infection, but it does make us miserable, and symptoms can last for up to a week.

If someone is infected with salmonella, they can take antibiotics. Most treatment, however, is palliative, focusing on the symptoms rather than on eliminating the cause. The main focus is getting fluids into the affected people — and making sure that we don’t contaminate our food with the bacterium in the first place.

So if we often get salmonella from contamination with raw chicken or eggs, what’s different across the ocean, in Europe?

An Egg’s Second Shell

When a chicken lays an egg, it has a thin, extra coating outside the shell for added protection, like putting clear coat on top of a piece of painted wood. That extra coating keeps the egg shielded against bacteria.

In the United States, we are concerned about the egg picking up salmonella from the dirty chickens that lay and interact with it — so all eggs must be washed, scrubbing them clean of bacteria (but also their shielding, meaning that they must then be refrigerated).

In most other countries, this coating is left on the shell. Because of this coating, the egg is more protected against bacteria and can be left out on shelves at supermarkets at room temperature.

Now, based on the above fact, you’d probably assume that the rates of salmonella are much higher in other countries, such as in Europe. After all, if they’re not cleaning the chicken-associated dirt off the shell, shouldn’t all their eggs be contaminated with salmonella?

In fact, salmonella rates are lower in Europe, with only around 108,614 Europeans reporting salmonella cases in 2009!

How are Europeans doing less cleaning, but still doing a better job of avoiding salmonella?

The answer comes down to a boogeyman of some Americans: a vaccine.