CDC is collaborating with public health officials in many states, the U.S. Department of Agriculture’s Food Safety and Inspection Service (FSIS), and the U.S. Food and Drug Administration (FDA) to investigate a multistate outbreak of Salmonella serotype Montevideo infections. Investigators are using DNA analysis of Salmonella bacteria obtained through diagnostic testing to identify cases of illness that may be part of this outbreak.
As of 9:00 pm EST on January 25, 2010, a total of 189 individuals infected with a matching strain of Salmonella Montevideo have been reported from 40 states since July 1, 2009. The number of ill persons identified in each state with this strain is as follows: AL (2), AZ (5), CA (30), CO (3), CT (4), DE (2), FL (2), GA (3), IA (1), ID (2), IL (11), IN (3), KS (3), LA (1), MA (12), MD (1), ME (1), MI (1), MN (4), MO (1), NC (9), ND (1), NE (1), NH (1), NJ (7), NY (15), OH (9), OK (1), OR (8), PA (3), RI (2), SC (1), SD (3), TN (4), TX (7), UT (7), VA (1), WA (14), WV (1), and WY (2). Because this is a commonly occurring strain, public health investigators may determine that some of the illnesses are not part of this outbreak.
Among the persons with reported dates available, illnesses began between July 4, 2009 and January 7, 2010. Infected individuals range in age from < 1 year old to 88 years old and the median age is 36 years. Fifty-three percent of patients are male. Among the 134 patients with available information, 37 (28%) were hospitalized. No deaths have been reported.
The outbreak can be visually described with a chart showing the number of persons who became ill each day. This chart is called an epidemic curve or epi curve. Illnesses that occurred after January 8, 2010 might not yet be reported due to the time it takes between when a person becomes ill and when the illness is reported. This takes an average of 2 to 3 weeks. Please see the Salmonella Outbreak Investigations: Timeline for Reporting Cases for more details.
Investigation of the Outbreak
A widely distributed contaminated food product might cause illnesses across the United States. The identity of the contaminated product often is not readily apparent. In outbreaks like this one, identification of the contaminated product requires conducting detailed standardized interviews with persons who were ill. It may also require conducting interviews with non-ill members of the public ("controls") to get information about foods recently eaten and other exposures to compare with information from the ill persons. The investigation is often supplemented by laboratory testing of suspected products. In addition, investigators sometimes use purchase information provided by ill persons to trace suspect products back to the point of production. This process is labor-intensive and typically takes weeks. It is not always successful.
During January 16-21, 2010, CDC and public health officials in multiple states conducted an epidemiologic study by comparing foods eaten by 41 ill and 41 well persons. Preliminary analysis of this study has suggested salami as a possible source of illness. Ill persons (58%) were significantly more likely than well persons (16%) to report eating salami. Additionally, 13 ill persons have been identified who purchased the same type of sliced salami variety pack at different grocery store locations before becoming ill. These data suggest this product may be the source of some of these illnesses. This sliced salami variety pack was recently recalled by Daniele International Inc. On January 23, 2010, FSIS issued a notice that Daniele International Inc. is recalling approximately 1,240,000 pounds of ready-to-eat varieties of Italian sausage products (including salame/salami) in commerce and potentially available to customers in retail locations because they may be contaminated with Salmonella. (www.fsis.usda.gov/News_&_Events/Recall_006_2010_Release/index.asp). These products can have an extended shelf life of up to one year. The manufacturer has voluntarily halted production of salami products.
This recall followed isolation of Salmonella in a private laboratory from a retail sample of a salami product produced by Daniele International; this product was different than the sliced salami variety pack purchased at different grocery store locations by the 13 ill persons. FSIS reviewed and affirmed these private laboratory results. The Salmonella strain initially found by the private laboratory was different from the strains causing the outbreak. However, the Washington State Department of Health subsequently tested the bacterial culture provided by the private laboratory (the salami was not provided) and identified two different Salmonella serotypes, the strain found by the private lab and Salmonella Montevideo indistinguishable from the outbreak strain. In addition, the Iowa Department of Public Health and public health officials in Plymouth County, Iowa investigated a patient with Salmonella Montevideo infection indistinguishable from the outbreak strain and discovered an open sliced salami variety pack frozen at the patient’s home. The patient had eaten this product before becoming ill. This sliced salami variety pack was the same as that purchased by 13 other ill persons. Using DNA analysis, the University of Iowa Hygienic Laboratory (Iowa’s public health laboratory) confirmed that the Salmonella isolated from this leftover salami was indistinguishable from the outbreak strain of Salmonella Montevideo.
CDC and its public health partners are continuing the epidemiologic investigation to verify that the outbreak is controlled; to identify the specific products or ingredients that became contaminated and how the contamination occurred; and to identify any other food vehicles that may be involved. It is possible that more than one food product may be causing illnesses. The investigation is ongoing.