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Technical Information — Measuring the Scope of Clostridium difficile Infection in the United States

Background

The Clostridium difficile infection (CDI) surveillance is a core component of the CDC’s Emerging Infections Program Healthcare-Associated Infections Community Interface (HAIC) activity. The EIP’s C. diff infection surveillance is an active population- and laboratory-based surveillance in selected counties in 10 US states. Trained surveillance epidemiologists in the 10 EIP sites investigate all positive C. difficile toxin assay or molecular assay reports from clinical, reference and commercial laboratories for residents of surveillance catchment areas. Residents who have a positive stool specimen for C. difficile greater than 8 weeks after the last positive specimen and are ≥1 year of age are considered new cases of C. diff infection. For each C. diff infection case identified a case report form with basic demographic, clinical and risk factor information is completed. C. diff infection cases are further classified into three epidemiologic categories: healthcare facility-onset (HCFO), if positive C. difficile stool specimen was collected greater than 3 calendar after hospital admission or in a resident of a long term care facility; community-onset healthcare facility-associated (CO-HCFA), if positive stool specimen was collected in an outpatient setting or within 3 days after hospital admission in a person with documented healthcare exposure (i.e. history of hospitalization or long-term care facility residency in the 12 weeks before stool specimen collection); and community–associated (CA) if positive stool specimen was collected in an outpatient setting or within 3 calendar days in a person with no documented healthcare exposure. For a subset of C. diff infection cases identified, isolates are sent to CDC for molecular characterization.

EIP C. diff infection surveillance also provides an infrastructure for further public health research, including special studies aiming at identifying risk factors for disease, population targets for vaccine, and monitoring effectiveness of prevention strategies. EIP C. diff infection surveillance was launched in 2009 in 7 EIP sites. It currently operates in 10 EIP sites across the United States and has approximately 11.1 million people under surveillance.

EIP C. diff infection data can be used to measure the burden of C. diff infection in the population, to monitor trends in disease overtime, and to characterize C. difficile strains responsible for C. diff infection and changes in the prevalence of these strains overtime.

 

Surveillance Objectives

  • Determine the population-based incidence of community– and healthcare–associated C. diff infection among participating EIP sites.
  • Characterize C. difficile strains that are responsible for C. diff infection in the population under surveillance with a focus on strains from community–associated cases.
  • Describe the epidemiology of community– and healthcare–associated C. diff infection and generate hypotheses for future research activities using EIP C. diff infection surveillance infrastructure.

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Methods

  • Surveillance Population

    The table below illustrates the population under surveillance for each EIP site as of December 2011.

    State Surveillance sites Estimated C. diff infection Surveillance Population
    CA San Francisco County 815,358
    CO Adams, Arapahoe, Denver, Douglas, Jefferson Counties 2,430,207
    CT New Haven County 846,101
    GA Clayton, Cobb, DeKalb, Douglas, Fulton, Gwinnet, Newton, Rockdale Counties 3,893,877
    MD Caroline, Cecil, Dorchester, Frederick, Kent, Somerset, Talbot, Queen Anne’s, Washington, Wicomico Worcester Counties 813,866
    MN Benton, Morrison, Stearns and Todd Counties 245,900
    NM Bernalillo County 642,527
    NY Rochester County 733,703
    OR Klamath County 66,247
    TN Nashville County 635,710
    TOTAL —————— 11,123,496
  • Case Definition

    C. diff infection Incident Case

    A case of C. diff infection is defined as a positive C. difficile toxin assay or a positive C.difficile molecular assay (e.g. PCR) on an incident stool specimen from a resident of the surveillance catchment area who is 1 year of age or older. Cases with a C. difficile positive stool specimen greater than 8 weeks after the last positive specimen are considered a new case with an incident stool specimen. Therefore, for surveillance purposes an individual may be classified and captured as a new incident case if eight consecutive weeks have elapsed since their last test positive for C.difficile.

    Recurrent episodes

    C. diff infection cases with a positive C. difficile stool specimen between 2 to 8 weeks of the last positive specimen are considered recurrent episodes.

    Duplicate episodes

    C. diff infection cases with a positive C. difficile stool specimen less than 2 weeks since the last positive specimen are considered duplicate episodes.

  • Case Ascertainment

    C. diff infection cases are identified using positive C. difficile toxin assay or C. difficile Nucleic Acid Amplification assay from all healthcare facility-based clinical laboratories as well as outpatient diagnostic clinical laboratories serving the population of surveillance catchment areas. Each laboratory serving surveillance catchment populations regularly provides line listings of positive C. difficile test results to the local EIP site. The line listings include the patient name and local laboratory identifier, date of specimen collection, as well as any additional available information (e.g. address, date of birth, age, sex, location of stool collection). Information on additional positive specimens from the same patient is recorded for the purpose of ascertaining and tracking recurrent or duplicate episodes, as well as, new cases (i.e. greater than eight weeks after the last positive C. difficile specimen). Case report forms are not completed on recurrent or duplicate episodes or patients determined to reside outside the catchment area.

  • Laboratory Characterization

    A convenience sample of stool specimens from incident C. diff infection cases with complete clinical and epidemiologic information are sent to reference laboratories for C.difficile isolation. Isolates recovered are then sent to CDC for molecular investigation including pulsed-field gel electrophoresis (PFGE), polymerase chain reaction (PCR), toxinotyping and mutation analysis.

  • Laboratory Audits

    Routine clinical laboratory audits are a fundamental requirement of the EIP C. diff infection surveillance. The purpose of conducting an audit is to assess whether the EIP C. diff infection Surveillance is capturing all cases through active surveillance and ensure that any change in incidence is not a surveillance artifact.

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Special Studies

  • Clostridium difficile Household Study at MN EIP Site

    Objectives:

    1. Evaluate the degree of household contamination with C. difficile including toxigenic strains
    2. Demonstrate comparability or differences in recovery from case and control households
    3. Compare isolates obtained from environment with isolates from humans and pets by molecular typing
    4. Determine the prevalence of and risk factors for C. difficile colonization and infection among household members and pets (cats and dogs) across different subsets of cases of C. diff infection.

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Publications

  1. Impact of North American Pulsed-field Type 1 (NAP1) Clostridium difficile Strain on Disease Severity and Outcome http://shea.confex.com/shea/2011/webprogram/Paper4843.html
  2. Epidemiology of Community-associated Clostridium difficile infection (CA-CDI), Emerging Infections Program, 2009-2011. Abstract presented at the 2012 Anaerobe Meeting, June 29-July 1,San Francisco, CA [PDF - 142 KB]
  3. Annual Reports and Findings
    • Surveillance Reports – none available at this time

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