Multistate Outbreak of Salmonella Enteritidis Infections Linked to Bean Sprouts (Final Update)

Introduction

CDC collaborated with public health officials in several states and the U.S. Food and Drug Administration (FDA) to investigate a multistate outbreak of Salmonella Enteritidis infections. Results from this investigation indicated that bean sprouts produced by Wonton Foods, Inc. were the likely source of this outbreak.

Public health investigators used the PulseNet system to identify illnesses that were part of this outbreak. PulseNet is the national subtyping network of public health and food regulatory agency laboratories coordinated by CDC. DNA "fingerprinting" is performed on Salmonella bacteria isolated from ill persons using a technique called pulsed-field gel electrophoresis, or PFGE. PulseNet manages a national database of these DNA fingerprints to identify possible outbreaks. Two PFGE patterns were included this investigation. Both PFGE patterns are rarely reported to the PulseNet database. On average, fewer than 10 types of Salmonella bacteria with these PFGE patterns are reported to PulseNet each year. Whole genome sequencing, a highly discriminatory subtyping method, was also performed on 16 of the clinical isolates, and all 16 were determined to be highly related to one another.

A total of 115 persons infected with the outbreak strains were reported from 12 states. The number of ill people identified in each state was as follows: Connecticut (8), Maine (4), Maryland (6), Massachusetts (36), Montana (1), New Hampshire (6), New York (22), Ohio (3), Pennsylvania (18), Rhode Island (7), Vermont (3), and Virginia (1). The one ill person from Montana traveled to the Eastern United States during the period when likely exposure occurred.

Illness onset dates ranged from September 30, 2014, to December 15, 2014. Ill persons ranged in age from younger than 1 year to 83 years, with a median age of 32 years. Sixty-four percent of ill persons were female. Among 75 persons with available information, 19 (25%) were hospitalized, and no deaths were reported.

This outbreak appears to be over. However, sprouts are a known source of foodborne illness. CDC recommends that consumers, restaurants, and other retailers always follow food safety practices to avoid illness from eating sprouts.

Investigation of the Outbreak

In interviews, ill persons answered questions about foods eaten and other exposures during the week before they became ill. Of 85 ill persons for whom information was known, 61 (72%) reported consuming bean sprouts or menu items containing bean sprouts in the week before they became ill. This proportion was significantly higher than results from a survey [PDF – 29 pages] of healthy persons in which 6% reported eating bean sprouts in the week before they were interviewed. Most ill persons reported consuming bean sprouts at Asian-style food service establishments.

In this investigation, state and local officials identified five clusters of illnesses in three states: Massachusetts, Rhode Island, and Vermont. Among the ill persons who were part of these illness clusters, all reported consuming menu items that contained bean sprouts. Investigating clusters of illnesses can provide critical clues about the source of an outbreak. A cluster of illnesses is defined as more than one unrelated ill person (i.e., they do not know or live with each other) who report eating at the same restaurant location, attending a common event, or shopping at the same location of a grocery store before becoming ill. If several unrelated ill persons ate or shopped at the same location of a restaurant or store within several days of each other, it suggests that the contaminated food item was served or sold there. In addition, traceback of suspected food items to identify a common point of contamination may be facilitated by records kept at these locations.

State and local public health officials, along with FDA, performed traceback investigations on the source of bean sprouts for all five illness clusters as well as for several individual ill persons. Traceback from all of the establishments indicated that all received bean sprouts from Wonton Foods, Inc. of Brooklyn, New York. Although some restaurants also received bean sprouts from other suppliers, Wonton Foods, Inc. was the only supplier common to all of the restaurants and was the sole supplier of bean sprouts to at least two of the restaurants.

On November 21, 2014, Wonton Foods, Inc. agreed to destroy any remaining products while they conducted thorough cleaning and sanitization and implemented other Salmonella control measures. On November 24, the firm completed cleaning and sanitization and restarted production of bean sprouts. The firm resumed shipment of bean sprouts on November 29, 2014. Contaminated bean sprouts produced by Wonton Foods, Inc. are likely no longer available for purchase or consumption given the maximum 12-day shelf life of mung bean sprouts.

CDC's National Antimicrobial Resistance Monitoring System (NARMS) laboratory conducted antibiotic resistance testing on Salmonella Enteritidis isolates collected from three ill persons infected with the outbreak strains. All three isolates were susceptible to all antibiotics tested on the NARMS panel.

Final Case Count Update

A total of 115 persons infected with the outbreak strains were reported from 12 states. The number of ill people identified in each state was as follows: Connecticut (8), Maine (4), Maryland (6), Massachusetts (36), Montana (1), New Hampshire (6), New York (22), Ohio (3), Pennsylvania (18), Rhode Island (7), Vermont (3), and Virginia (1). The one ill person from Montana traveled to the Eastern United States during the period when exposure likely occurred. Since the last update on December 16, 2014, four additional cases were reported from Maryland (1), Massachusetts (1), New York (1), and Pennsylvania (1).

Illness onset dates ranged from September 30, 2014, to December 15, 2014. Ill persons ranged in age from younger than 1 year to 83 years, with a median age of 32 years. Sixty-four percent of ill persons were female. Among 75 persons with available information, 19 (25%) were hospitalized, and no deaths were reported.

This outbreak appears to be over. However, sprouts are a known source of foodborne illness. CDC recommends that consumers, restaurants, and other retailers always follow food safety practices to avoid illness from eating sprouts.

Case Count Update

As of December 2, a total of 87 persons infected with the outbreak strains of Salmonella Enteritidis have been reported from 11 states. Since the last update on November 25, 2014, 19 additional ill persons have been reported from Connecticut (3), Massachusetts (4), New York (9), Ohio (2), and Virginia (1).

Illness onset dates range from September 30, 2014 to November 14, 2014. Ill persons range in age from younger than 1 year to 83 years, with a median age of 32 years. Fifty-nine percent of ill persons are female. Among 52 persons with available information, 14 (27%) have been hospitalized, and no deaths have been reported.

Illnesses that occurred after November 12, 2014 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 4 weeks. Please see the Timeline for Reporting Cases of Salmonella Infection for more details.

Investigation Update

On November 21, 2014, Wonton Foods, Inc. agreed to destroy any remaining products while they conducted thorough cleaning and sanitization and implemented other Salmonella control measures. On November 24, the firm completed cleaning and sanitization and restarted production of bean sprouts. The firm resumed shipment on November 29, 2014. Contaminated bean sprouts produced by Wonton Foods, Inc. are likely no longer available for purchase or consumption given the maximum 12-day shelf life of mung bean sprouts.

CDC's National Antimicrobial Resistance Monitoring System (NARMS) laboratory conducted antibiotic resistance testing on Salmonella Enteritidis isolates collected from three ill persons infected with the outbreak strains; all three isolates were susceptible to all antibiotics tested on the NARMS panel.

CDC and state and local public health partners are continuing laboratory surveillance through PulseNet to identify additional ill persons and to interview them about foods they ate before they became ill. This investigation is ongoing, and CDC will update the public when additional information is available.

Case Count Update

As of November 24, a total of 68 persons infected with the outbreak strains of Salmonella Enteritidis have been reported from 10 states. The number of ill people identified in each state is as follows: Connecticut (4), Maine (3), Massachusetts (31), Montana (1), New Hampshire (4), New York (5), Ohio (1), Pennsylvania (10), Rhode Island (6), and Vermont (3). The one ill person from Montana traveled to the Eastern United States during the period when likely exposure occurred.

Illness onset dates range from September 30, 2014 to November 10, 2014. Ill persons range in age from younger than one year to 83 years, with a median age of 31 years. Fifty-six percent of ill persons are female. Among 43 persons with available information, 11 (26%) have been hospitalized, and no deaths have been reported.

This 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 November 4, 2014 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 4 weeks. Please see the Timeline for Reporting Cases of Salmonella Infection for more details.

Investigation Update

CDC's National Antimicrobial Resistance Monitoring System (NARMS) laboratory is currently conducting antibiotic resistance testing on clinical isolates collected from ill persons infected with the outbreak strains of Salmonella Enteritidis. Results of this testing will be reported when they become available. NARMS is a U.S. public health surveillance system that tracks antimicrobial resistance in foodborne and other enteric bacteria found in people, raw meat and poultry, and food-producing animals. NARMS is an interagency partnership among the CDC, the US Food and Drug Administration (FDA), the USDA, and state and local health departments. The NARMS human surveillance program monitors antibiotic resistance in Salmonella, Campylobacter, Shigella, Escherichia coli O157, and Vibrio bacteria isolated from clinical specimens and submitted to NARMS by public health laboratories.

CDC and state and local public health partners are continuing laboratory surveillance through PulseNet to identify additional ill persons and to interview them about foods they ate before they became ill. This ongoing investigation is rapidly evolving, and CDC will update the public when additional information is available.

November 21, 2014

CDC is collaborating with public health officials in several states and the U.S. Food and Drug Administration (FDA) to investigate a multistate outbreak of Salmonella Enteritidis infections. Results from this ongoing investigation indicate that bean sprouts produced by Wonton Foods, Inc. are the likely source of this outbreak.

Public health investigators are using the PulseNet system to identify illnesses that may be part of this outbreak. PulseNet is the national subtyping network of public health and food regulatory agency laboratories coordinated by CDC. DNA "fingerprinting" is performed on Salmonella bacteria isolated from ill persons using a technique called pulsed-field gel electrophoresis, or PFGE. PulseNet manages a national database of these DNA fingerprints to identify possible outbreaks. Two PFGE patterns are included this investigation. Both PFGE patterns are rarely reported to the PulseNet database. On average, less than 10 Salmonella bacteria with these PFGE patterns are reported to PulseNet each year.

As of November 21, 2014, a total of 63 persons infected with the outbreak strains of Salmonella Enteritidis have been reported from 10 states: Connecticut, Maine, Massachusetts, Montana, New Hampshire, New York, Ohio, Pennsylvania, Rhode Island, and Vermont. The one ill person from Montana traveled to the Eastern United States during the period when likely exposure occurred. Illness onset dates range from September 30, 2014 to November 8, 2014. Among 42 persons with available information, 11 (26%) have been hospitalized, and no deaths have been reported.

Investigation of the Outbreak

In interviews, ill persons answered questions about foods eaten and other exposures during the week before they became ill. Of 37 ill persons for whom information is known, 29 (78%) reported consuming bean sprouts or menu items containing bean sprouts in the week before they became ill. This proportion is significantly higher than results from a survey [PDF – 788 KB] of healthy persons in which 6% reported eating bean sprouts in the week before they were interviewed. Most ill persons reported consuming bean sprouts at Asian-style food service establishments.

In this investigation, state and local officials have identified five clusters of illnesses in three states: Massachusetts, Rhode Island, and Vermont. Among the ill persons who are part of these illness clusters, all reported consuming menu items that contained bean sprouts. Investigating clusters of illnesses can provide critical clues about the source of an outbreak. A cluster of illnesses is defined as more than one unrelated ill person (i.e., they do not know or live with each other) who report eating at the same restaurant location, attending a common event, or shopping at the same location of a grocery store before becoming ill. If several unrelated ill persons ate or shopped at the same location of a restaurant or store within several days of each other, it suggests that the contaminated food item was served or sold there. In addition, traceback of suspected food items to identify a common point of contamination may be facilitated by records kept at these locations.

State and local public health officials also performed traceback investigations on the source of bean sprouts for all five illness clusters as well as for several individual ill persons and reported the results of these investigations to FDA and CDC. Traceback from all of the establishments indicated that all received bean sprouts from Wonton Foods, Inc. of Brooklyn, New York. Although some restaurants also received bean sprouts from other suppliers, Wonton Foods, Inc. was the only supplier common to all of the restaurants and was the sole supplier of bean sprouts to at least two of the restaurants. The firm is cooperating with public health and agriculture officials and has reported that their last shipment of bean sprouts was on November 18, 2014. As of November 21, 2014, the firm has verbally agreed to voluntarily stop the production and sale of their bean sprouts while they take steps to prevent Salmonella contamination.

CDC and state and local public health partners are continuing laboratory surveillance through PulseNet to identify additional ill persons and to interview them about foods they ate before they became ill. This ongoing investigation is rapidly evolving, and CDC will update the public when additional information is available.