An outbreak of an especially strong form of salmonella has sickened hundreds of people in 20 states. But how it happened largely has remained a mystery. Here's what we know about some of the more pressing questions surrounding the outbreak. Have other questions? Email the reporter at firstname.lastname@example.org.
What led to the salmonella outbreak?
It's still unknown. Foster Farms, the company that owns the processing plants linked to the outbreak, hasn't said if it knows. Federal regulators suspect the bacteria spread when whole chickens were cut into parts to be packaged and sold, which is after the point regulators test for salmonella.
Chicken from those plants is still being sold. Why?
It is legal to sell chicken in the United States that has salmonella in it.
Food recalls technically are voluntary, but the U.S. Department of Agriculture has not encouraged Foster Farms to pull chicken from these three California plants out of supermarkets.
"We have to be confident that what we decide to pull out of the market is what we can support in the evidence," said Daniel Engeljohn, assistant administrator with the USDA's Food Safety and Inspection Service.
The company and the government say you should be fine if you properly cook and handle the meat.
So why did so many people get so sick?
The strains of salmonella Heidelberg implicated in the outbreak are especially strong. They are antibiotic-resistant, which means that drugs that normally would be able to kill the bacteria or stop its growth don't work.
Why are these bacteria antibiotic-resistant?
Some livestock are fed antibiotics to make them grow faster and to prevent and treat disease. The bacteria in livestock have responded, leading to an increase in the prevalence of antibiotic-resistant bacteria.
That's bad news for humans who get infected with the bacteria. Antibiotic resistance may contribute to the bacteria's virulence and make it harder to treat infection in humans.
We can see evidence of that toll in the current outbreak; 40 percent of the reported victims have been hospitalized. That is about twice the typical hospitalization rate in a salmonella outbreak.
Why didn't this problem get caught earlier by USDA inspectors?
The food inspection system is designed to flag plants that have especially high amounts of the bacteria in their meat, but testing is infrequent.
The three Foster Farms plants in question had such good records on salmonella that their whole chicken carcasses were tested by federal inspectors about every two years. The results of those tests did not foreshadow any problems. Even subsequent testing after the outbreak started found rates of salmonella on chicken parts in the plants only slightly higher than the typical plant.
While inspectors found some safety violations in the plants, they were not appreciably different from other plants around the country.
"Right now, the evidence we have is that the production process was not out of control," Engeljohn said. "It can be improved, but it was not out of control."
Why didn't the USDA shut down the plants when officials knew about the problems?
On Oct. 7, the agency threatened to shut down the plants by pulling its inspectors but did not actually do so. That's because Foster Farms assured federal inspectors that it was making changes to improve its processes. One change the company has pledged to make is introducing an antimicrobial treatment on chicken parts.
Europe seems to be doing better with salmonella. What are nations there doing that the U.S. isn't?
While the U.S. has made no progress in cutting the incidence of salmonella infections in humans since 1996, the European Union cut its infections by almost half between 2004 and 2009.
Some countries, such as Sweden, have greatly reduced salmonella in chickens sold for food. But they have done so in part by aggressively managing the human pathogen in flocks, killing infected birds by the tens of thousands.
What is the U.S. doing to control salmonella at chicken farms?
In the United States, federal inspectors do not monitor chickens being raised for slaughter for human pathogens such as salmonella Heidelberg. In fact, the USDA's Food Safety and Inspection Service has no jurisdiction over chickens at that stage. It starts looking at the birds when they are brought to the plants to be killed and processed, like the Foster Farms facilities in Central California.
If you eat chicken, how can you protect yourself from salmonella?
To kill the bacteria in raw chicken, it should be cooked to at least 165 degrees, according to Foodsafety.gov.
It sounds counterintuitive, but do not wash your raw chicken. That's a common way that cross-contamination occurs in the home kitchen.
"Anything it touches -- your hands, your sink, your counter -- treat it like it is contaminated and clean it up afterwards," said Jean Weese, professor of poultry science at Auburn University.