Why Salmonella Strikes Ground Meat

08/05/2011 08:26 am ET | Updated Oct 05, 2011

You are likely aware of an outbreak of salmonella, provisionally linked at this point to ground turkey and prompting a massive recall. If so, you have likely also heard -- as if garden variety salmonella weren't bad enough -- that this particular bug is resistant to multiple antibiotics, and thus causes an infection that is very hard to treat. Thus far, the origins of this specific outbreak are uncertain. But the general origins of an antibiotic-resistant salmonella outbreak involving ground meat are not mysterious, nor are the required measures for self-defense. So let's get to it.

Salmonella is an intestinal organism and always on the short list of bugs causing food-borne outbreaks. Unlike some of the other bad actors -- shigella and various strains of E. coli -- salmonella infections, though nasty, are generally self-limited. When they are mild, recovery occurs without antibiotics. When more severe, antibiotics are usually effective. The salmonella species that most often cause food-borne outbreaks are native to various animals, and are thus called "zoonotic" infections, meaning they are passed from animal species to humans.

Why is chopped meat -- in this case, turkey -- a particular problem? Basically, because of surface area. (As an aside, I recall that whenever in doubt about the answer to a question in 7th grade biology, "increases the surface area" was likely to get at least partial credit because it is such an important biological principle. In public health, when in doubt, the best guess tends to be "age and sex.")

Intestinal bacteria that contaminate meat contaminate the portion that is exposed -- namely the surface. In general, when the exposed surface of meat is heated adequately (that temperature varies with the kind of meat, but a ballpark figure is 165˚ F), the bacteria is killed.

There are two problems with chopped meat. First, the inside is the outside and vice versa. Chopping meat massively increases the surface area, allowing the bacteria to invade throughout. And, because meat at the very center of a burger, patty, meatball or meatloaf could well have been on the surface at some point, contaminating bacteria are only reliably killed if the temperature throughout reaches the relevant threshold. Because the entire area of chopped meat is surface area, it should be eaten well-cooked.

The second issue with chopped meat is that it generally comes from multiple animals -- in the case of ground meat prepared at centralized processing facilities, possibly quite a large number. The risks of bacterial contamination rise in this situation, because even one infected animal may contribute germs to meat being sent all over the country. When you eat un-chopped meat, the source is a single animal.

Finally, there is the issue of antibiotic resistance. This is a straight-forward case of survival of the fittest. The more bacteria are exposed to antibiotics, the more vulnerable bugs die leaving only the resistant bugs alive. Those resistant bugs then replicate and pass along their resistance. Very often, the resistance traits come along with some disadvantage, so in the absence of routine antibiotic exposure, the non-resistant bugs can come to predominate again. The propagation of antibiotic-resistant germs in our food supply, and in general, owes much to the routine dosing of feed animals with antibiotics.

Which brings us to self-defense. Worrisome though a salmonella outbreak may be, you can reliably defend yourself and your family.

Cook meat well. Temperature guidelines are readily available. In particular, be sure to heat chopped meat all the way to the center. Other options include avoiding chopped meat, and/or making your own with a small meat grinder. If you grind your own meat, you know the source is a single animal. This does not obviate the need to cook well, but reduces the likelihood of there being any bad bugs around in the first place.

Do not let uncooked meat touch any other food items in your home. This is food safety 101, but had to be said. If germs from meat get onto food that will not be cooked, then cooking the meat is no longer a reliable defense.

The other measures of self-defense depend more on the body politic. The routine use of antibiotics in feed animals should be avoided -- as should the crowding that is often the basis for this practice. If you eat meat, you might limit your intake to animals from farms you know that avoid antibiotics, crowding and any unnatural feeding practices. We would, of course, see a decline in food-borne infections if as a society we simply ate less meat overall -- but that's a topic for another day.

Even good self-defense can occasionally fail, so it's also important to know the symptoms of salmonella infection so you can get prompt medical attention if you need it.

For now, the exact origins of the current outbreak remain a mystery -- but the means of defending yourself and your family from it are not. With a word of thanks to your 7th grade biology teacher, put them to good use.