AN INTERNATIONAL OUTBREAK OF SALMONELLA INFECTIONS CAUSED BY ALFALFA SPROUTS GROWN FROM CONTAMINATED SEEDS

An outbreak of Salmonella serotype stanley infections occurred in the United States and Finland in 1995. The outbreak was investigated throu gh case-control studies in Arizona, Michigan, and Finland; by isolate subtyping; and by tracing and culturing of the implicated food. Alfalf a sprout consumption was the only exposure associated with S. stanley infections in Arizona (matched odds ratio [MOR] = 11.1; 95% confidence interval [CI], 1.4-513), Michigan (MOR = 5.5; CI, 1.6-23), and Finlan d (MOR undefined; CI, 4.9-infinity). US and Finnish patient isolates w ere a unique outbreak strain distinct from S. stanley isolates not lin ked to the outbreak. Alfalfa sprouts eaten by patients in 6 US states and Finland were traced to seed shipped by a Dutch shipper, Thus, it w as concluded that alfalfa sprouts grown from contaminated seed caused an international outbreak of greater than or equal to 242 S. stanley i nfections in greater than or equal to 17 US states and Finland. This o utbreak illustrates a new mechanism through which contamination of fre sh produce can cause large, widely dispersed outbreaks.