WASHINGTON (AP) -- A type of salmonella found in eggs is turning up more often in chicken meat and needs to be reduced, according to the Agriculture Department.

From 2000 through 2005, there was a fourfold increase in positive test results for salmonella enteritidis on chicken carcasses.

"It still continues to rise, even though the overall incidence of salmonella in general has fallen," said Richard Raymond, the Agriculture Department undersecretary for food safety. "It's one that we still don't have all the scientific evidence we need to know how best to attack it."

Salmonella sickens at least 40,000 people and kills about 600 every year in the United States.

Many different salmonella bacteria make people sick, but salmonella enteritidis is one of the most common. It causes fever, stomach cramps and diarrhea, and in vulnerable people, infection can turn deadly by spreading beyond the intestine to the bloodstream.

It used to be that eggs got contaminated with salmonella on the outside, from contact with fecal bacteria. But in recent years, the salmonella enteritidis strain has been found inside intact, disinfected, grade A eggs. This type of germ contaminates eggs inside a hen's ovaries, before shells are even formed.

Now the germ is turning up in broiler chickens, the kind used for meat, according to research by the Agriculture Department published in the December issue of the Emerging Infectious Diseases journal of the Centers for Disease Control and Prevention.

The research found:

-Positive tests for salmonella enteritidis increased fourfold from 2000 through 2005.

-The proportion of plants with positive tests for salmonella enteritidis increased threefold during that time.

-The number of states with positive tests for salmonella enteritidis rose from 14 to 24.

The research was done before the Agriculture Department started a new program to reduce positive tests for salmonella.

Since then, the incidence of salmonella has fallen from 18 percent in 2005 to 10 percent today, Raymond said.

"Even though that particular bug is going up, the overall incidence of food-borne illness from salmonella is declining, and the amount of salmonella positives have shown a dramatic drop," Raymond said.

Cooking poultry to 165 degrees will kill the salmonella germ. The government also strongly recommends that people use food thermometers and follow basic rules for kitchen safety: wash hands often, keep raw poultry and meat separate from cooked food, and refrigerate or freeze food right away.

However, a recent CDC study on food poisoning from salmonella noted that the risk of illness from salmonella enteritidis increased the less people ate at home.

"This measure may, in fact, be considered to be a proxy for eating a larger number of commercially prepared meals," the CDC found.

That study said that while overall infections from salmonella were lower than in the mid-1990s, infections from salmonella enteritidis were 25 percent higher.

While salmonella is commonly found in poultry, it is found in many other products, from pork and beef to raw fruits and vegetables and dairy products.

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