The largest egg recall in nearly a decade has people understandably spooked. Here's how Salmonella gets into eggs in the first place.

Yesterday, we reported on a Salmonella outbreak that left 22 people sick and led to a recall of over 206 million eggs.

Salmonella is a bacteria and, if a person gets infected, the symptoms include fever, diarrhea, nausea, vomiting, and abdominal pain.

Of the estimated 1.1 million Salmonella infections originating from the United States per year, 1 million are transferred by food, according to the Centers for Disease Control and Prevention. These cases lead to 19,000 hospitalizations and 380 deaths annually.

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Understandably, the news about potentially contaminated eggs causing the largest egg recall since 2010 has people worried, and many are wondering how Salmonella even gets into eggs at their local grocery stores in the first place.

According to the CDC, Salmonella enteritidis–the strain that makes people sick via eggs–can get into eggs two ways. The first is by indirect or environmental contamination, which is when feces in the environment penetrates shell once an egg is out of the hen.

Salmonella can also be in eggs that appear normal via direct transmission, which are born from hens that exhibit no symptoms of illness. The eggs are contaminated internally, meaning Salmonella can get into eggs while they're still in a hen's ovaries. To make the illness even more enigmatic, hens infected with Salmonella can lay completely healthy eggs in addition to those that will cause sickness.

The New York Times noted at the time of the 2010 egg recall that Salmonella enteritidis in chicken eggs first appeared in the 1970s and 80s, although the "why?" and "how?" aren't exactly clear. One theory in the article credits the decreased immunity of chickens to new strains of Salmonella because of limited exposure to related strains.

According to the Centers for Disease Control and Prevention, there are steps to take at various levels of the farm-to-table chain to limit the chances of a Salmonella outbreak: the government can enact policy changes, health care providers can educate about food safety, farmers can implement prevention-focused safety systems, and at the consumer level, everyone should clean all utensils and countertops thoroughly.

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If you're looking for more precautionary measures, always keep your raw foods separate from ready-to-eat foods, don't consume uncooked meats and poultry, and keep your fridge below 40 degrees Fahrenheit.

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