Barry Estabrook

The results are in.

Earlier this month I speculated that the root cause of the recent food-borne epidemics like the Salmonella outbreak was to be found in the very nature of large-scale, industrialized agriculture: vast cacophonous barracks reeking of fumes from ammonia and housing 50,000 to 125,000 caged hens, debeaked to prevent them from pecking each other to death, then packed into "battery" cages so tightly that they can't turn around or flap their wings.

Why could my 12 hens be constantly exposed to the same unsanitary evils as the 7 million Wright County battery chickens and still lay Salmonella-free eggs?

From an admittedly unscientific point of view, I considered my own backyard hens. As they peck and scratch through their daily routine, they encounter rodents, wild birds, manure, and cats, all cited by the Food and Drug Administration as examples of the filthy conditions under which the Iowa-based Wright County Egg chickens responsible for the outbreak lived. Yet my birds have never sickened anyone.

A reader suggested that I should get my eggs tested. "You might be surprised at the strains of salmonella they contain," he wrote. I accepted the challenge. The lab tests came back last week. No Salmonella.

Which left me relieved, but puzzled. Why could my 12 hens be constantly exposed to the same unsanitary evils as the 7 million Wright County battery chickens and still lay Salmonella-free eggs? Does raising chickens under free-range conditions make them less susceptible to Salmonella?

My reader suggested that perhaps the care I took in handling my eggs—cleaning their shells and cooking them to high enough temperatures to kill Salmonella—was the reason there have been no problems. As much as I'd like to say that's true, I don't necessarily scrub the shells of my eggs, and I'm a confirmed sunny-side-up man; my partner likes hers soft-boiled.

Some background: Salmonella enteritidis, the strain currently sickening Americans, lives in chickens' intestines. Sometimes it migrates to their uteruses. Eggs can become contaminated either on the outside of their shells through contact with feces, or internally before they are laid. (Here's a good description of how the bacteria get in eggs.)

Barry Estabrook

One explanation for why my eggs were Salmonella-free might have been that the odds to begin with were highly in my favor. Even in areas of high contamination, only one egg in 10,000 will become infected because infected hens shed the bacteria intermittently, according to Patrick McDonough, a bacteriologist at Cornell University's veterinary school. McDonough added that my chickens probably arrived at my coop from the hatchery as healthy chicks and had never been exposed to the bacteria.

Another reason might be that raising chickens under a free-range system makes them less susceptible to Salmonella. "I don't think there is any doubt about it that healthy chickens living in decent surroundings are just going to be a lot more resistant to Salmonella," said John L. Ingraham, emeritus professor of microbiology at the University of California-Davis, and author of the book March of the Microbes , recently published by Harvard University Press. "Take any creature, ourselves included, you put them in terrible stressful conditions and they become susceptible to disease."

Ingraham, who happens to maintain 13 laying hens, also suspects that the massive doses of antibiotics fed to confined farm animals could be a factor in the spread of Salmonella. "Antibiotics kill off healthy, normal intestinal flora. That gives Salmonella a good chance to get started there," he said.

Recent studies of hens in France and Great Britain confirm that birds that are allowed to roam are less likely to get Salmonella than those kept in confinement.

Ingraham has no qualms about making traditional Caesar Salad dressing and mayonnaise—both of which involve uncooked eggs—with eggs from his own flock. "I'd be afraid to do that with a supermarket egg," he said.

Me too.