CDC has several surveillance systems for obtaining information about Salmonella. They serve different purposes and provide information on various features of the organism’s epidemiology, such as number of outbreaks, antimicrobial-resistant infections, and subtypes.

Laboratory-based Enteric Disease Surveillance (LEDS)

Collects laboratory data, such as serotype, on Salmonella

National Salmonella surveillance data are collected through passive surveillance of laboratory-confirmed human Salmonella isolates. Clinical diagnostic laboratories submit Salmonella isolates to state and territorial public health laboratories, where they are confirmed and serotyped according to the Kauffmann-White scheme. Unusual or untypable serotypes are forwarded to the Centers for Disease Control and Prevention’s (CDC) National Salmonella Reference Laboratory at the Enteric Diseases Laboratory Branch (EDLB) for further characterization or confirmation; results are reported back to state and territorial public health laboratories.

State and territorial public health laboratories send reports electronically to CDC through a variety of mechanisms. Initially, all surveillance data were transmitted through the Public Health Laboratory Information System (PHLIS), but other methods of data transmission have been implemented over time; currently data are collected into the Laboratory-based Enteric Disease Surveillance (LEDS) system, which has replaced PHLIS. The Division of Foodborne, Waterborne, and Environmental Diseases (DFWED) in the National Center for Emerging and Zoonotic Infectious Diseases maintains the national Salmonella surveillance data in LEDS. The annual summaries of these data are the only regularly published national source of serotype information for Salmonella.


National Notifiable Diseases Surveillance System (NNDSS)

Tracks notifiable infectious diseases across the US

The National Notifiable Disease Surveillance System, or NNDSS, tracks contagious diseases that laboratory professionals and doctors are required to report to the state or territorial public health agency. These agencies voluntarily submit the information to NNDSS, which CDC oversees. The general system has been in existence since 1878. Notifiable disease surveillance is “passive” (i.e., the investigator at CDC waits for disease reports from those required to report) and is susceptible to underreporting. Foodborne diseases that are reportable include botulism, hemolytic uremic syndrome (HUS), listeriosis (Listeria), salmonellosis (Salmonella), Shiga Toxin-producing Escherichia coli (STEC) infections, and vibriosis (cholera and its relatives).


Foodborne Disease Active Surveillance Network (FoodNet)

Reports trends in foodborne infections and tracks the impact of food safety policies nationally

Foodborne Diseases Active Surveillance Network, referred to as FoodNet, is the principal foodborne disease component of CDC’s Emerging Infections Program. FoodNet is a sentinel surveillance system¹ that collects information from sites in 10 states—covering 15% of the US population, or 46 million Americans—about diseases that are caused by any of seven bacteria and two parasites² commonly transmitted through food. The system has been in operation since 1995. Investigators actively seek out laboratory confirmed cases of illness in an attempt to detect every person in the 10 sites who went to a doctor’s office, had a sample tested, and was diagnosed with one of these infections. With the information on epidemiology, incidence, and trends of foodborne diseases in the US, public health officials can conduct analyses and epidemiological studies.

FoodNet is a collaborative program among CDC, the U.S. Department of Agriculture’s Food Safety and Inspection Service (USDA-FSIS), the Food and Drug Administration (FDA), and state health departments in Connecticut, Georgia, Maryland, Minnesota, New Mexico, Oregon, Tennessee, and selected counties in California, Colorado, and New York.


National Molecular Subtyping Network for Foodborne Disease Surveillance (PulseNet)

Connects cases of illness nationwide to quickly identify outbreaks, including many that would otherwise go undetected

The National Molecular Subtyping Network for Foodborne Disease Surveillance, or PulseNet, connects cases to potential outbreaks, especially across states. PulseNet has revolutionized the detection and investigation of foodborne disease outbreaks, especially those occurring in multiple sites across the country which, before PulseNet, often went undetected or were detected only after they grew very large. Analysis is done through subtyping and categorization of foodborne bacterial pathogens though a standardized process of pulsed-field gel electrophoresis (PFGE)3. PulseNet is a national network of local, state, territorial, agricultural, and federal laboratories—in all 50 states and 82 countries—coordinated by CDC and the Association of Public Health LaboratoriesExternal (APHL) since 1996. PulseNet allows investigators from participating sites to upload PFGE patterns to an electronic database and compare them with patterns of other pathogens isolated from humans, animals, and foods to identify matches and possible linkages between pathogens (e.g., outbreaks).


National Antimicrobial Resistance Monitoring System—enteric bacteria (NARMS)

Tracking trends in resistance

The National Antimicrobial Resistance Monitoring System (NARMS) is a collaboration among state and local health departments, CDC, FDAExternal, and USDAExternal. NARMS monitors antimicrobial resistance in enteric (intestinal) bacteria isolated from humans, retail meats, and food animals.  CDC’s primary role is to track and report antibiotic resistance in enteric bacteria isolated from people who have infections caused by Salmonella, Campylobacter, Escherichia coli O157, Shigella, or Vibrio species other than V. cholerae.


Foodborne Disease Outbreak Surveillance System (FDOSS)

Captures outbreak data on agents, foods, and settings responsible for illness

CDC collects reports of foodborne outbreaks due to enteric bacterial, viral, parasitic, and chemical agents. State, local, and territorial public health agencies report these outbreaks to the Foodborne Disease Outbreak Surveillance System through the National Outbreak Reporting System (NORS). The CDC surveillance team conducts analyses of these data to improve understanding of the human health impact of foodborne outbreaks and the pathogens, foods, settings, and contributing factors (for example, food not kept at the right temperature) involved in these outbreaks. Though this system has existed since 1973, starting in 2009, the system has also included modules for reporting enteric disease outbreaks transmitted through water, person-to-person contact, or direct contact with animals. The data transmission tool that preceded NORS was called the electronic Foodborne Outbreak Reporting System (eFORS) from 1998-2008.

NORS data are published online in NORS Dashboard, an online data tool that provides public access to nearly 20 years of information on foodborne, waterborne, and other enteric (intestinal) disease outbreaks. The interactive maps, graphs, and charts in NORS Dashboard help users learn about outbreaks caused by bacteria, viral, parasitic, and chemical agents. For more information, see NORS Dashboard Q&A.


CDC’s Outbreak Response Team (ORT) works to ensure rapid, coordinated detection and response to multistate foodborne outbreaks of enteric diseases and to promote comprehensive outbreak surveillance and investigation. It also seeks to improve the collaboration and partnership among officials in local, state, and federal agencies who detect and respond to foodborne enteric disease outbreaks.


1Sentinel surveillance involves the collection of case data from only part of the total population (from a sample of providers) to learn something about the larger population, such as trends in disease. (source)

2Campylobacter, Cryptosporidium, Cyclospora, Listeria, Salmonella, Escherichia coli O157 and non-O157, Shigella, Vibrio, and Yersinia

3PFGE is a technique used to distinguish between strains of organisms, such as different types of E. coli and Salmonella. By applying an electric field that constantly changes direction to a gel matrix, large DNA molecules are separated, which allows scientists to see the unique DNA pattern—or “fingerprint”—of the organism and compare it to others.