Eggs and salmonella contamination


As the scope of the nationwide salmonella outbreak expanded late last month, farmers market vendors reported rushes on locally produced eggs and people with backyard flocks were sitting smug.

But food safety experts say consumers shouldn’t jump to the conclusion that locally produced eggs are any safer than eggs from large commercial suppliers.

“Salmonella and chickens go together,” says Casey Barton Behravesh, a veterinary epidemiologist with the Centers for Disease Control and Prevention’s division of food-borne, water-borne and environmental disease. “Any chicken, whether it’s from a huge farm or a backyard flock, may have salmonella.”

If anything, eggs from large-scale producers should, theoretically, be safer, says Charles Scanlan, a professor of veterinary medicine specializing in food-borne pathogens at Texas A&M University in College Station. That’s because commercial egg farms are subject to state and federal regulations requiring inspections and regular testing for pathogens, including salmonella.

Commercial farms have another advantage, says Theresia Lavergne, professor of poultry science at the Louisiana State University AgCenter in Baton Rouge. At such farms, she says, chickens are typically kept in cages with slanted bottoms; their eggs roll out of the cages right after they’re laid, leaving little chance for the eggs to come into contact with hen feces.

Rise in outbreaks

But neither regulations nor slanted cages are a guarantee against outbreaks. Chickens infected with salmonella excrete the germ in their feces, which can contaminate egg shells. On rare occasions, the germ infects a hen’s ovaries and can end up inside the eggs she lays.

And just because commercial producers are required to test for and monitor pathogen levels, that doesn’t mean they’ve always done so on a routine basis. (New, tighter federal regulations governing U.S. poultry farms went into effect in July, however.)

What’s more, when pathogens contaminate a flock at a large commercial farm, “the problem becomes a huge, national problem very quickly,” says Michele Jay-Russell, food safety specialist at the Western Institute for Food Safety and Security at UC Davis. (Consider, for example, the half-billion eggs recalled in the recent outbreak.)

Buying local eggs — or a few chickens to keep in the yard — is one way to avoid recalled eggs without much thought. But backyard producers should take precautions to avoid infection with salmonella and also campylobacter, another foodborne pathogen common to chickens, Lavergne says.

Backyard eggs should be collected often, washed in water between 90 and 120 degrees Fahrenheit, dried immediately and stored in the back of the fridge, where they’ll stay coldest, she says. (Washing with very warm water expands the egg’s contents, so any dirt on the shell won’t push its way through the shell’s pores.)

For those buying eggs at farmers markets, Jay-Russell advises against purchasing or collecting eggs with visible feces, feathers or cracks on them.

Backyard rules

There’s little evidence that salmonella levels are any different in commercial birds compared to birds housed at smaller farms or in backyards, Jay-Russell adds. A 1996 study published in the journal Avian Disease found higher levels of a specific type of salmonella in free-range compared to caged birds. But a 2004 study conducted by researchers at the Poultry Microbiological Safety Research Unit at the Richard B. Russell Agricultural Research Center in Athens, Ga., found no difference in salmonella levels in free-range chickens compared to conventionally raised chickens.

Backyard flocks have been implicated in a number of salmonella outbreaks linked to handling chicks, which tend to have higher salmonella levels than adult birds. Since the 1990s, the CDC has documented 28 salmonella outbreaks linked to contact with baby chicks in small flocks, Behravesh says — in the summer of 2009 alone, there were four such outbreaks, a record number for a single season. She suspects the rise in the number of outbreaks is linked to the growing popularity of backyard bird-keeping.

To limit the risk of salmonella infection from backyard flocks, the CDC recommends that children younger than 5 not handle birds without supervision and that families never allow birds in the house (even — and especially — as little chicks); never eat or drink near the birds and their coop; and wash hands thoroughly after any contact with birds, eggs or the coop.

“Having backyard chickens can be a lot of fun and part of a greener, healthier lifestyle,” Behravesh says, “but people need to be aware that any chicken can shed salmonella.”