ATLANTA — Hold the salsa—tomato-related Salmonella outbreaks are a growing problem.
A multicounty outbreak of Salmonella enteritidis in the San Francisco Bay area of California in 2005 was traced to overripe tomatoes sold by a single grower. This is the first evidence of S. enteritidis associated with tomatoes in California, Dr. Jean W. Yuan reported at the International Conference on Emerging Infectious Diseases.
The number of Salmonella isolates in California increased significantly—by nearly threefold—in 2005 compared with 2004, noted Dr. Yuan of the Centers for Disease Control and Prevention and the California Department of Health Services. “We noticed a statewide increase in S. enteritidis, and we identified two restaurant clusters with S. enteritidis in geographically distinct locations with no common food handler,” Dr. Yuan said. “We wondered if there was a common source for the statewide increase and the restaurant clusters.”
Overall, 67% of the patients had eaten fresh salsa in restaurants, compared with 23% of controls, based on a case-control study of 79 patients who developed S. enteritidis from July 1 to July 18, 2005. These patients were significantly more likely than controls to have eaten in one of two affected Mexican restaurant chains.
The outbreak was especially noteworthy because it involved phage type 30, “a rare phage type that we had not detected in California residents before,” Dr. Yuan said. “The only previous phage type 30 outbreak had been attributed to raw almonds from California.”
The investigators examined the salsa ingredients and found that tomatoes and cilantro were significantly associated with illness. No common source was identified for cilantro, but a traceback investigation of the suspected tomatoes identified a common tomato grower and packer who supplied tomatoes to the affected restaurants.
“This grower-packer sells tomatoes in cash transactions only, when they are too ripe to sell to regular customers,” Dr. Yuan said. “Many Mexican restaurants prefer the cheaper, riper tomatoes because of the high volume of tomatoes they use on a daily basis.”
“Uncooked tomatoes are an integral and nutritious part of the American diet, and the potential for future outbreaks is a concern,” Dr. Yuan added.