Updated

The Agriculture Department says three California poultry processing facilities linked to a salmonella outbreak in raw chicken can stay open.

Foster Farms, which owns the facilities, has made “immediate substantive changes to their slaughter and processing to allow for continued operations,” the department said.

Regulators threatened this week to shut down the plants. Sampling in September showed that raw chicken processed by those facilities included strains of salmonella that were linked to the outbreak that has sickened 278 people in 17 states.

The government said inspectors would monitor the company’s improvements and sample Foster Farms meat for the next three months.

The Centers for Disease Control and Prevention said that the outbreak, which began in March, was continuing and that some illnesses began as recently as two weeks ago. The majority of the illnesses have been in California.

The outbreak has heightened concerns because it has a high rate of hospitalizations. The C.D.C. said 42 percent of victims had been hospitalized, about double the normal rate, and the salmonella strain involved is resistant to many antibiotics, making it more dangerous.

In a statement released Wednesday, the president of Foster Farms, Ron Foster, said the company was cooperating with the investigation and had put new food safety controls in place after it found out about the illnesses.

“Foster Farms is dedicated to resolving any concerns by the U.S.D.A.,” Mr. Foster said.

Salmonella can contaminate meat during slaughter and processing and is especially common in raw chicken. The infections can be avoided by proper handling and cooking of raw poultry.

The pathogen causes diarrhea, abdominal cramps and fever within a few days of eating a contaminated product and can be life-threatening to those with weakened immune systems.