At least 15 people became ill with Salmonella infections last month after attending the Margarita Mix-Off in Chico, California.  Three of the fifteen were hospitalized due to the severity of their illnesses.

The Margarita Mix-Off was hosted at Manzanita Place in Chico on May 8, with six local restaurants providing food served at the event.  Butte County public health officials have thus far been unable to determine the source of the outbreak despite conducting extensive interviews with people who got sick.

Public health officials reportedly thought the Chico Salmonella outbreak was part of a nationwide Salmonella outbreak that had been detected among people who consumed alfalfa sprouts, but lab tests showed that the Salmonella bacteria isolated from ill Margarita Mix-Off attendees and people who had eaten sprouts had different “genetic fingerprints” and no sprouts were served at the event.

In a statement (pdf) released yesterday by Butte County Public Health, Health Officer Mark Lundberg, M.D., said that the sub-type of Salmonella identified in the Chico outbreak is relatively rare.

Although there does not appear to be any ongoing transmission, Butte County Public Health is conducting an investigation to determine what may have caused the outbreak.

Salmonella is one of the most common enteric (intestinal) infections in the United States. Salmonellosis–the illness caused by the ingestion Salmonella bacteria–is the second most common bacterial foodborne illness after Campylobacter infection. It is estimated that 1.4 million cases of salmonellosis occur each year in the U.S.; 95 percent of those cases are related to foodborne causes.

The acute symptoms of Salmonella gastroenteritis include the sudden onset of nausea, abdominal cramping, and bloody diarrhea with mucous. Fever is almost always a symptom. Vomiting is less common than diarrhea. Headaches, muscle pain, and joint pain are often reported as well. The onset of symptoms usually occurs within 6 to 72 hours after the ingestion of Salmonella bacteria. The infectious dose is small, probably from 15 to 20 cells.

Salmonella bacteria are discovered in stool cultures. Although blood cultures are rarely positive, bacteremia (bacteria in the blood stream) does occur in 5 percent of adults with Salmonella gastroenteritis and can result in spread to the heart (endocarditis), spleen, bone (osteomyelitis), and joints (reactive arthritis).

Generally, blood cultures are not performed and in most cases the blood stream is not infected.  In the stool, the laboratory is challenged to pick out Salmonella from many other similar bacteria that are normally present. In addition, many people submit samples for testing after they have started antibiotics, which may make it even more difficult for a microbiology lab to grow Salmonella. So, the diagnosis of salmonellosis may be problematic and many mild cases are culture-negative.

Salmonella infections usually resolve in five to seven days, and many times require no treatment, unless the affected person becomes severely dehydrated or the infection spreads from the intestines.  Individuals with severe diarrhea may require re-hydration, often with intravenous fluids. Some Salmonella bacteria have become resistant to antibiotics, possibly as a result of the use of antibiotics to promote the growth of feed animals.

Anyone who attended the Margarita Mix-Off on May 8 and experienced diarrheal illness during the week of May 8 through May 15 is asked to call the Butte County Public Health Communicable Disease division at 891-2732 or 891-2863 from 8:00 a.m. to 5:00 p.m. to speak with a Public Health Nurse.