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December 2, 2010 (FINAL Update)
CDC collaborated with public health officials in multiple states, the U.S. Department of Health and Human Services’ Food and Drug Administration (FDA), and the U.S. Department of Agriculture’s Food Safety and Inspection Service to investigate a nationwide increase of Salmonella Enteritidis (SE) infections with an indistinguishable pulsed-field gel electrophoresis (PFGE) pattern JEGX01.0004. This is the most common PFGE pattern for SE in the PulseNet database. Investigators used DNA analysis of SE bacteria obtained through diagnostic testing to identify cases of illness and restaurant or event clusters (where more than one ill person with the outbreak strain had eaten) that may have been part of this outbreak. Because the SE PFGE pattern commonly occurs in the United States, some of the cases identified may not have been related to this outbreak.
In July 2010, CDC identified a nationwide sustained increase in the number of Salmonella Enteritidis isolates with PFGE pattern JEGX01.0004 uploaded to PulseNet, the national subtyping network made up of state and local public health laboratories and federal food regulatory laboratories that performs molecular surveillance of foodborne infections. An increase in reports beginning in May, peaking in July, and returning to baseline in November, is evident in the epidemic curve, or epi curve. From May 1 to November 30, 2010, a total of 3,578 illnesses were reported. However, some cases from this period may not have been reported yet, and some of these cases may not be related to this outbreak. Based on the previous 5 years of reports to PulseNet, we would expect approximately 1,639 total illnesses to occur during this same period. This means there are approximately 1,939 reported illnesses that are likely to be associated with this outbreak. Because of the large number of expected cases during this period, standard methods of molecular subtyping alone are not sufficient to determine which reported cases might be outbreak-associated.
Human Salmonella Enteritidis infections that occurred after October 28, 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 typically takes two to three weeks for Salmonella, but can take up to six weeks. For more details, please see the Salmonella Outbreak Investigations: Timeline for Reporting Cases.
Epidemiologic investigations conducted by public health officials in 11 states since April identified 29 restaurants or event clusters where more than one ill person with the outbreak strain had eaten. Data from these investigations suggest that shell eggs were a likely source of infections in many of these restaurants or event clusters. Wright County Egg, in Galt, Iowa, was an egg supplier in 15 of these 29 restaurants or event clusters. Traceback investigations were completed for several of these clusters. A formal traceback was conducted by state partners in California, Colorado, and Minnesota, in collaboration with FDA and CDC, to find a common source of shell eggs. Wright County Egg in Iowa was found as the common source of the shell eggs associated with four of the clusters. Through traceback and FDA investigational findings, Hillandale Farms of Iowa, Inc., was identified as another potential source of contaminated shell eggs contributing to this outbreak. FDA has now completed its on-site investigations of both Iowa farms and an evaluation of the investigational data, including review of sampling results and records. FDA’s inspectional observations, in addition to sample results, indicate substantial potential for Salmonella to have persisted in the environment and to have contaminated eggs (see 483 Inspectional Observations on the Egg Recall).
FDA collected nearly 600 samples from Wright County Egg and Hillandale Farms of Iowa during this investigation. Samples underwent subtyping testing. FDA's testing of 11 environmental samples identified Salmonella with PFGE patterns indistinguishable from the outbreak strain. Samples were collected from manure, as well as traffic areas such as walkways, equipment, other surfaces in and around the farm, and from the feed mill at Wright County Egg in Iowa. The feed was provided to pullets (young female chickens or hens) raised at Wright County Egg facilities in Iowa. Pullets were distributed to all premises at Wright County Egg in Iowa and Hillandale Farms in Iowa. A positive sample was also collected from egg water wash in a packing facility at Hillandale Farms of Iowa. These findings indicate that Wright County Egg and Hillandale Farms of Iowa were the likely sources of the contaminated shell eggs. FDA did not find that this feed was distributed to any companies other than Wright County Egg and Hillandale Farms of Iowa.
On August 13, 2010, Wright County Egg of Galt, Iowa, conducted a nationwide voluntary recall of shell eggs. On August 18, 2010, Wright County Egg expanded its recall. On August 20, 2010, Hillandale Farms of Iowa conducted a nationwide voluntary recall of shell eggs. At this point, it is long past the expiration date of any eggs affected by the recall.
While this particular outbreak appears to be over, Salmonella Enteritidis is still an important cause of human illness in the United States. A person infected with Salmonella Enteritidis usually has fever, abdominal cramps, and diarrhea beginning 12 to 72 hours after consuming a contaminated food or beverage. The illness usually lasts 4 to 7 days, and most persons recover without antibiotic treatment. However, the diarrhea can be severe, and hospitalization may be required. The elderly, infants, and those with impaired immune systems may have a more serious illness. In these patients, the infection may spread from the intestines to the blood stream, and then to other body sites and can cause death unless the person is treated promptly with antibiotics. For more information, visit CDC’s Salmonella Enteritidis website.
As an agency within the U.S. Department of Health and Human Services (HHS), CDC leads federal efforts to gather data on foodborne illnesses, investigate foodborne illnesses and outbreaks, and monitor the effectiveness of prevention and control efforts. CDC is not a food safety regulatory agency but works closely with the food safety regulatory agencies, in particular, with HHS’ Food and Drug Administration (FDA) and the Food Safety and Inspection Service within the U.S. Department of Agriculture. CDC also plays a key role in building state and local health department epidemiology, laboratory, and environmental health capacity to support foodborne disease surveillance and outbreak response. Notably, CDC data can be used to help document the effectiveness of regulatory interventions.
NOTICE: The information on this page is no longer being updated and may have changed. The information is accurate only as of the last page update.
Content source: Centers for Disease Control and Prevention
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)
Division of Foodborne, Waterborne,and Environmental Diseases (DFWED)