“Salmonella Thrives in Cage Housing”—This headline was featured in World Poultry in 2009. In 2010, an outbreak of salmonella that sickened hundreds of people caused the recall of hundreds of millions of eggs in the United States.

All 15 studies published comparing salmonella contamination in cage and cage-free egg operations since 2005 founder higher rates of salmonella in the cage facilities. The only two studies ever published comparing risk at the consumer level both tied increased salmonella risk to cage egg consumption.

The health risks posed by battery cages are easy to understand; when birds are crammed so tightly together in cages, with thousands and thousands of hens housed in single barns, the transmission bacteria and of diseases such as bird flu happens much more easily than if hens are afforded more room to move.

Hens are typically jammed into cage-filled sheds by the hundreds of thousands, causing environmental degradation—especially manure-related pollution. For this reason, numerous environmental organizations are in favor of the egg industry switching to cage-free systems.

Studies have shown that not confining animals in cages may improve food safety.