ATLANTA, Georgia (CNN) -- The Centers for Disease Control and Prevention is working with public health officials in 42 states to determine the cause of an outbreak of a particular type of salmonella called Typhimurium.
Salmonella bacteria are transmitted to humans by eating contaminated foods.
According to CDC sources, at least 388 people have been infected with this strain since September 3, but most cases occurred between October 1 and December 31, the disease agency said. About 18 percent of cases were hospitalized as a result of their illness, and patients have ranged from two months to 98 years of age.
California is reporting the highest case count with 55, followed by Ohio with 53 cases, Massachusetts with 39, Minnesota with 30 and Michigan with 20.
The other 37 states are each reporting anywhere from one to 19 cases.
The eight states that have not reported any cases connected to the outbreak are Montana, New Mexico, Louisiana, Mississippi, South Carolina, Florida, Alaska and Hawaii.
King Nut peanut butter was identified as the source of an outbreak that may have contributed to one death in Minnesota, state public health officials said Friday in a news release. CNN was unable to reach the company for comment.
CDC has not identified what food or foods might be causing this outbreak.
CDC officials and state public health workers are conducting case control studies, which means they're tracking down people who have been infected as early as September to determine what they may have consumed, to find a common cause. 
Learn more about salmonella »
The Food and Drug Administration and the U.S. Department of Agriculture are in contact with the CDC, but without a determination of the cause of the outbreak, their involvement is limited.
Various strains of salmonella have been linked to previous outbreaks, caused by contaminated eggs, meat, poultry, vegetables, pet food and even peanut butter.
Contaminated tomatoes were blamed for a salmonella Typhimurium outbreak in fall 2006, which sickened at least 183 people in 21 states. Most of the victims had diarrhea and fever for about a week. Nobody died in that outbreak.
Salmonella infections are caused by bacteria and if necessary can be treated with antibiotics, although some strains have become resistant to these drugs, according to the CDC Web site. Most people infected will develop diarrhea, fever and abdominal cramps within a few days of infection, and their illness can last up to a week.
Most recover without any treatment, but some may suffer dehydration and in severe cases require hospitalization.
The youngest and oldest patients and chronically ill people with compromised immune systems are at highest risk for severe complications, according to the National Institutes of Health.
Until a cause of the outbreak is confirmed, the CDC is recommending the following:
Consumers should thoroughly cook meats, poultry and eggs. They should also avoid consuming raw or unpasteurized milk and other dairy products. Produce should be thoroughly washed as well.
Avoid cross-contamination of uncooked meats and produce to prevent spreading any potential salmonella. Frequent washing of hands during food preparation can also help reduce cross-contamination.
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