WASHINGTON (AP) -- An outbreak of antibiotic-resistant salmonella linked to a California chicken producer continues to sicken people more than a year after it started.

Despite the illnesses, producer Foster Farms has not initiated a recall, and the government has no apparent plans to shut it down.

The federal Centers for Disease Control says there were 50 new reported illnesses in the last two months, bringing to 574 the total number of cases in the outbreak. Most of the illnesses are in California.

Though centered on the West Coast, the outbreak is widespread — victims came from 27 states and Puerto Rico. There have been no known deaths.

The Agriculture Department says it is closely monitoring Foster Farms facilities and that measured rates of salmonella in the company's products have been going down. The department threatened to shut down Foster Farms' facilities last year but let them stay open after the company said it had made immediate changes to reduce salmonella rates.

Food safety advocates say it is long past time to pressure the company for a recall and to shut down production.

"It's very unclear why USDA isn't taking more action to stop the sale of the product and protect the public," says Caroline Smith DeWaal of the Center for Science in the Public Interest.

Foster Farms said this week that it has put new measures in place, including tighter screening of birds, improved safety on the farms where the birds are raised and better sanitation in its plants. The company suggested that the recent cases may be because salmonella incidence increases in the warmer months.

Dealing with outbreaks is nothing new for Foster Farms. The company was linked to salmonella illnesses in 2004 and then again in 2012, before the current outbreak, which started in 2013.

In a letter from USDA to Foster Farms last October, the department said inspectors had documented "fecal material on carcasses" along with "poor sanitary dressing practices, insanitary food contact surfaces, insanitary nonfood contact surfaces and direct product contamination."

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In January, USDA inspectors briefly closed a Foster Farms plant after finding cockroaches.

Recalls of poultry contaminated with salmonella are tricky because the law allows raw chicken to have a certain amount of salmonella — a rule that consumer advocates have long lobbied to change. Because salmonella is so prevalent in poultry and is killed if consumers cook it properly, the government has not declared it to be an "adulterant," or illegal, in meat, as is E. coli. Outbreaks of salmonella in poultry can take longer to discover and recalls don't happen as quickly.

Because of those rules, USDA would likely have to go through the courts if it decided to force a recall.

In a statement, USDA spokeswoman Catherine Cochran said the outbreak "has persisted for far too long without a solution." She said the agency is continuing to investigate the illnesses, "including the possibility that they may be caused by other sources."

The CDC, however, is focused on Foster Farms. The agency said three-fourths of victims who were able to provide the CDC with brand information said they had consumed chicken produced by Foster Farms before becoming ill. Thirty-seven percent of victims were hospitalized and 13 percent of the victims had developed blood infections, almost three times the normal rate.

The CDC's Ian Williams says they are seeing a slow decline in the number of illnesses. "It suggests to us that they are starting to address the problem," Williams says.

However, Williams says many more people have likely been sickened than are reported — the CDC routinely multiplies reported salmonella cases by 20 to 30, meaning up to 17,000 people could have been infected in the current outbreak.

USDA has not released a comprehensive list of where Foster Farms is sold. Last year, Costco and Kroger-owned stores took Foster Farms products off their shelves. Neither company responded to a request for comment on whether they are selling it again.

Foster Farms also did not respond to a request for comment on retail outlets.

Rick Schiller of San Jose, California, says he became severely ill last September after baking and eating some Foster Farms chicken he had in his freezer. He eventually ended up in the hospital, and says he still has weakness on the right side of his body due to complications from his treatment.

"It should have been recalled a long time ago," Schiller says. "The government is just dropping the ball and people could lose their lives over this."

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