Washington: An outbreak of salmonella food poisoning has made 388 people sick across 42 states, sending 18 percent of them to the hospital, U.S. health officials said on Wednesday.

The U.S. Centers for Disease Control and Prevention is trying to trace the source of the outbreak, which began in September. The Department of Agriculture, state health officials and the Food and Drug Administration are also involved.

The CDC said poultry, cheese and eggs are the most common source of this particular strain, known as Salmonella typhimurium.

"It is often difficult to identify sources of food-borne outbreaks. People may not remember the foods they recently ate and may not be aware of all of the ingredients in food. That's what makes these types of investigations very difficult," said CDC spokesman David Daigle.

Daigle did not specify how many people were hospitalized, but the percentage he gave puts that figure at about 70.

"Because foods of animal origin may be contaminated with Salmonella, people should not eat raw or undercooked eggs, poultry, or meat. Persons also should not consume raw or unpasteurized milk or other dairy products. Produce should be thoroughly washed," he said.

Only Ohio state health officials have agreed to have their state named as one of those affected, with an estimated 50 cases.

Every year, approximately 40,000 people are reported ill with salmonella in the United States, the CDC says, but it said many more cases are never reported.

There have been several recent high-profile outbreaks of food-borne illness in the United States, including a strain of Salmonella carried by peppers from Mexico and that sickened 1,400 people from April to August of 2007 and an E. coli epidemic in 2006, traced to California spinach, that killed three.

Salmonella-contaminated dry pet food sickened at least 79 people, including many young children, in October and November.

Source : Reuters