Smaller flocks, more Salmonella

WRITTEN BY: Kerry Evans

I like eggs - scrambled, fried, poached, you name it. What I don’t like is Salmonella. A new study from Pennsylvania State University found that eggs from small flocks are more likely to be contaminated with Salmonella than eggs from large commercial flocks.

Salmonella enteritidis causes egg-associated Salmonellosis. S. enteritidis is a rod-shaped Gram-negative bacterium. Egg-eating humans can become infected with these bacteria in a couple of different ways. First, the outsides of eggs can be contaminated with chicken fecal matter. Salmonella is part of a chicken’s normal gut flora, so it’s easy for eggs to become contaminated. Luckily, strict rules about sanitizing the eggs have eliminated this as a point of infection (for the most part).

On the other hand, a chicken’s ovaries can become infected with Salmonella. When this happens, Salmonella can find its way inside of the eggs (a Trojan horse, if you will). This is why it’s especially important to cook your eggs thoroughly, ensuring that any bacteria are destroyed.

The Penn State researchers wanted to know how the safety of eggs from large flocks compared to eggs from small flocks. Over a period of 6 months, they purchased eggs from 240 farmers’ markets or roadside stands from across 67 counties in Pennsylvania. Then, they sampled the outsides and insides of the eggs for Salmonella.

What they found was surprising - 2% of the eggs tested positive for S. enteritidis. This is a higher incidence of contamination than is seen with large commercial flocks. Of the 5 contaminated eggs, only 1 had S. enteritidis on its outer shell. Bacteria were found inside the other 4 eggs, indicating that these chickens had ovarian infections.

According to study author Subhashinie Kariyawasam, "We were curious about Salmonella contamination of eggs produced by these flocks because the prevalence of this pathogen in smaller flocks was not known. Now we know that the prevalence of Salmonella enteritidis in eggs produced by small flocks is higher than in eggs produced by larger flocks."

What’s the take-home message? Cook your eggs thoroughly - small flocks aren’t subject to federal regulations like the FDA Final Egg rule. “If you buy your eggs from the small producers”, says Kariyawasam, “you need to worry about Salmonella just as if you bought eggs produced by large flocks. And, beyond the consumption of eggs, birds in these flocks can have Salmonella, so people with backyard poultry need to be aware of the dangers with pet birds - there is a risk to allowing birds to come into the house and children playing with the chickens.”