Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to page options Skip directly to site content

Salmonella, Shiga toxin-producing Escherichia coli, and Listeria (SSL) Metrics

The FoodCORE performance metrics are a list of measurable activities covering diverse aspects of outbreak response. These activities span from outbreak surveillance and detection through investigation, response, control, and prevention measures. Using the metrics, each center provides data about the burden, timeliness, and completeness of foodborne disease activities related to the key areas of activity. A table of FoodCORE cumulative SSL metrics data for Year One (October 2010 to September 2011) is available.

Metrics in bold represent the minimum reporting requirements for FoodCORE Centers

Isolate/Specimen-based Metrics

  1. Measures for Salmonella, STEC (Shiga toxin-producing Escherichia coli), or Listeria (SSL) isolates/isolate-yielding specimens submitted to or recovered at the Public Health Laboratory (PHL).
    1. Total number of SSL isolates and isolate-yielding specimens
    2. Number of SSL primary isolates/isolate-yielding specimens
  2. Measures for STEC clinical specimens or samples received at PHL
    1. Total number of preliminary positive STEC clinical specimens or samples received at PHL (regardless of if isolate-yielding or not).
    2. #(%) isolate yielding STEC specimens or samples
  3. Measure time from SSL isolation /isolate-yielding specimen collection to receipt at PHL
  4. Measure time from receipt of SSL isolate-yielding specimens at PHL to recovery of isolate
  5. Measure % of Salmonella primary isolates with complete serotype information and % of STEC primary isolates with serotype information (n/a for Listeria isolates)
  6. Measure time from SSL isolate receipt (or recovery) at PHL to serotype result
  7. Measure % of SSL primary isolates with PFGE information
  8. Measures for PFGE timeliness
    1. Measure time from SSL isolate receipt (or recovery) at PHL to PFGE upload to PulseNet
    2. Measure time from SSL isolate receipt (or recovery) at PHL to receipt at the PFGE laboratory
 Top of Page

Case-based Metrics

  1. Measure number of laboratory confirmed SSL cases reported to epidemiology staff
  2. Measures for case-based interview statistics
    1. % of SSL cases with attempted interview
    2. Measure time from SSL case report to initial interview attempt
    3. % of SSL cases with complete demographic data
    4. % of SSL cases with exposure history obtained
      1. % of SSL cases with full shotgun or case exposure completed
    5. % of SS cases with serotype information
    6. % of SSL cases with PFGE information
      1. % of SSL cases with PFGE where complete epidemiologic data is collected
    7. Record reason for not interviewing SSL cases (lost to follow-up, refused, time lag too long, other)
 Top of Page

Cluster-based Metrics

  1. Number of SSL clusters
  2. Measures for identified SSL clusters with epidemiologic activity or action
    1. #(%) of SSL clusters with routine interview of cases
    2. #(%) of SSL clusters with supplemental or targeted interviewing of cases
    3. #(%) of SSL clusters where an analytic epidemiologic study was conducted
  3. Measure #(%) of SSL clusters with suspect vehicle/source identified
  4. Measure #(%) of SSL clusters with confirmed vehicle/source identified
  5. Measures for SSL clusters with identified vehicle/source where control measures or public health actions were taken
    1. #(%) of SSL clusters with exclusion of a(an) ill person(s) from high risk setting
    2. #(%) of SSL clusters with remediation or closure of an establishment linked to illness
    3. #(%) of SSL clusters with educational campaigns during outbreaks (beyond individual case education)
    4. #(%) of SSL clusters with media or public messaging (web updates, press release, etc.)
    5. #(%) of SSL clusters with regulatory action (recall, hold, etc.)
  6. Measure #(%) of SSL clusters with link to a common location of exposures (e.g., restaurant, food establishment, nursing home, etc.) where an environmental health assessment was conducted
  7. Measure #(% )of SSL clusters where food or environmental sample collected for testing
  8. Measure #(%) of SSL clusters where environmental health, agriculture, regulatory, or food safety program staff were contacted.
 Top of Page

Outbreak-based Metrics

  1. Measure #(%) of SSL outbreaks where NORS form completed
 Top of Page


All measurements of time are in median days: Measurements will exclude weekend days. For laboratory time measurements, only isolates subtyped at the PHL should be included.

Isolate/Isolate-yielding specimen: This will include all SSL isolates (human, food, environmental, etc.) submitted to PHL and isolates recovered from specimen submitted to PHL. This can be further broken down to report total number of each category of isolates (human, food, environmental, etc.).

Primary isolates/isolate-yielding specimen: To be limited to the first or representative SSL isolate or sample for each case or testing unit for non-human isolates.

Laboratory confirmed SSL cases: Refer to NNDSS laboratory confirmed case definitions for each pathogen (

Complete demographic data: To include State, County, Birth Month, Birth Year, Sex, Race

Exposure history: To include an interview (of any format) that assesses exposures prior to onset of illness, via an open-ended exposure history, or via a list of potential exposures. The key factor to be considered an exposure history is an interview that goes beyond assessment of high-risk settings and prevention education to ascertain food consumption/preference, or other exposure data.

Complete epidemiologic data: To include complete demographic data as well as an exposure history.

SSL cluster: Two or more cases of Salmonella or STEC infection with an indistinguishable PFGE pattern in 60 days, or 120 days for Listeria infections, where the number of cases meets one or more of the following criteria:

  1. The number of PFGE-matched isolates represent an increase over the expected baseline
  2. Demographic or other epidemiologic characteristics among cases with PFGE-matched isolates indicate some deviation from expected values for the region
  3. There is a PFGE-matched non-human isolate that would indicate a potential source of human infections

In the absence of meeting the above criteria in a catchment area, a case-patient should be considered cluster-associated if the above criteria are met when including isolates from other jurisdictions or catchment areas.

In the absence of meeting any of the above criteria, ill persons should be considered cluster-associated if there are demographic or epidemiologic indications of a common source of infection even without laboratory subtyping data to link cases.

Above baseline: A significant deviation (either in the number of isolates or a change in the demographic/temporal characteristics of cases) from expected values based on historical (laboratory) data for a specific SSL serotype or PFGE pattern.

Investigation: Any active epidemiologic follow-up resulting from the identification of a cluster. This could be initiating contact with a case (or the public health authority under whose jurisdiction a case falls) to ascertain direct case-based epidemiologic data, or active review of previously collected case-based data for cases later identified as cluster-associated.

Notification: Report of a case or cluster (depending on the metric) to epidemiology staff, i.e., when epidemiology staff first were made aware of a specific case or an identified cluster. This could be via routine communication such as a laboratory report or accessing a database, or via direct complaints, reports from another health authority (local, other state, federal, etc.), media report, or other means of communication.

Analytic epidemiologic study: A systematic, statistical analysis against a comparison group or within a cohort to test a hypothesis

Vehicle/source Identified:

SUSPECT vehicle/source clusters: Clusters of infection where investigational and/or laboratory data indicate a likely source/vehicle of infection without confirmation: vehicle is a known risk factor, established errors in food preparation, or reported consumption by a high proportion of cluster-associated cases.

CONFIRMED vehicle/source clusters: Clusters of infection where the etiologic agent has either been cultured from the vehicle or the vehicle has been statistically implicated in an analytic study.

Control measure: to include interventions such as exclusion of an ill person(s) from high risk setting, remediation or closure of an establishment linked to illness, educational campaigns during daycare outbreaks, etc. To be considered a control measure, activities should extend beyond the routine educational component of an interview or exposure assessment.

Public health action: to include media, public messaging (web updates, press release, etc.) or regulatory action (recall, hold, etc.). To be considered a public health action, activities should extend beyond the routine investigation activities and reach at-risk individuals beyond identified cases. A public health action should be included in the SSL metrics if the FoodCORE Center was directly involved in the action, or is aware that a public health action was taken during a multijurisdictional investigation. For example, if CDC produces public messaging during a multistate outbreak investigation that a FoodCORE Center is involved in, that investigation would be associated with a public health action for the purposes of the metrics.

 Top of Page