Jun 4, 2004 (CIDRAP) An investigation of Salmonella illness cases associated with raw almonds has identified 29 cases in 12 states and one Canadian province, dating back as far as September 2003, the Centers for Disease Control and Prevention (CDC) reported today.
The cases triggered recalls of raw almonds by Paramount Farms, Lost Hills, Calif., totaling about 13 million pounds by May 21. Most of the almonds probably were eaten months ago, but consumers may still have some of them, since their shelf life is more than a year, the CDC said.
Seven of the patients were hospitalized, but no one died, the CDC states in a supplement to Morbidity and Mortality Weekly Report. A number of cases that occurred earlier in 2003 and involved Salmonella strains matching the outbreak strain are still under investigation.
"The current outbreak continued for months, and possibly for more than 1 year, without being detected," the CDC says. The first clue to the outbreak emerged May 12, when an Oregon state laboratory identified five patients infected with Salmonella enterica serotype Enteritidis organisms that were matched by using two-enzyme pulsed-field gel electrophoresis (PFGE), the article says.
Lengthy interviews with the patients about their eating and shopping in the days before their illness revealed that all had eaten Kirkland Signature raw almonds bought at Costco stores and that they had no other food exposures in common. By examining data from general food-consumption surveys in Oregon, investigators determined that an association between the five cases and the almonds was highly probable.
US and Canadian epidemiologists and health officials were notified of the outbreak, and laboratories were asked to check for reports of Salmonella Enteritidis organisms matching the outbreak strain, the CDC says. By Jun 2, 29 patients with Salmonella Enteritidis infections matching the two PFGE patterns had been found in 12 states and one Canadian province.
"Among 26 patients interviewed, 24 recalled eating raw almonds during the week before illness onset; 20 patients identified brands packaged or supplied by Paramount Farms," the article states. Through store computer records, dates and places of almond purchase were identified in 10 cases.
Investigators have not yet found Salmonella contamination in almonds from Paramount Farms, the CDC reports. Tests of almonds recovered from one patient's home and samples collected at Paramount were negative. However, Salmonella was found in one environmental sample collected at Paramount and in three samples from two almond huller-shellers that supplied Paramount during the outbreak period. PFGE tests of those samples have not yet been completed.
The CDC says it is not clear how almonds become contaminated with Salmonella, and California and federal officials are continuing to investigate. "Typical harvesting, drying, and hulling-shelling practices readily enable cross-contamination," the agency says.
The only previous salmonellosis outbreak associated with tree nuts was discovered in 2001, when raw almonds were linked to Salmonella Enteritidis cases, mostly in Canada, according to the CDC. The almonds were traced to three California orchards that were all contaminated with Salmonella Enteritidis with identical phage and PFGE patterns.
The article notes that California produces about 80% of the world's almonds and almost all almonds sold in the United States. The almonds subject to recall, besides being sold domestically, were exported to France, Italy, Japan, Korea, Malaysia, Mexico, Taiwan, and the United Kingdom.
CDC. Outbreak of Salmonella serotype Enteritidis infections associated with raw almondsUnited States and Canada, 2003-2004. MMWR 2004;53(Dispatch):1-3 [Full text]