FAQs: Multidrug-Resistant Organism & Clostridioides difficile Infection (MDRO & CDI)

Numerator Reporting for LabID Events: Definition of CDI Assay

For NHSN reporting purposes, a CDI LabID event is a positive laboratory test result for C. difficile toxin A and/or toxin B OR any detection of toxin-producing C. difficile organisms by culture or other laboratory means on an unformed stool specimen that conforms to the container. Testing methods include, but are not limited to, molecular assays such as PCR and/or toxin assays such as EIA.


If a multi-step testing algorithm is used to test for C. difficile toxins, refer to question #2 below.

The CDI lab result (Antigen Positive, Toxin Negative) does not meet NHSN definition of a CDI-positive laboratory assay since the toxin result is negative.

Numerator Reporting for LabID Events: Testing for CDI

Regardless of the method or sequence of testing, when testing the same unformed stool specimen, the result of the last test performed is used to determine if the CDI Laboratory Assay definition is met and a LabID event is submitted to NHSN.   Examples of different algorithms and interpretations for event reporting are provided in the MDRO protocol:  MDRO protocol [PDF – 2 MB].

Only when the final report has specific test times attached to each of the individual testing methods (for example, antigen/toxin and PCR) can one make a valid determination of which test is performed first and which is performed last. If there are no specific test times/time stamps attached to each individual testing method on the final lab report, consider the tests as performed simultaneously and any positive is eligible for use.

Numerator Reporting for LabID Events: Acceptable specimens for CDI reporting

NHSN doesn’t specify collection methods; Any unformed stool specimen testing positive for C. difficile toxin A and/or toxin B is eligible for use in meeting the definition of CDI laboratory assay. Reporting should be done irrespective of method of collection (for example, stools collected from ostomies), and/or there being a change from the normal consistency or amount of the stool.  These reporting instructions align with the intent of LabID Event Reporting to decrease the burden for gathering information beyond the specimen collection date and admission date and will remove subjectivity and simplify interpretation of the GI-CDI infection criteria.  Specimens labeled something other than ‘stool’ are not eligible for use.

Numerator Reporting for LabID Events: Primary Testing Method for CDI

The response should reflect the testing method used with the majority of specimens tested (the test used in more than 50% of all testing performed).  For example, a facility rotates between three testing methods, with the following proportions: NAAT only in 15% of specimens tested, GDH/EIA toxin in 45%, and GDH/EIA reflexed to NAAT for discrepant results in 40%.  The appropriate response is GDH/EIA given 85% of all testing is by GDH/EIA.  The response to the question is to be completed in the last month of each calendar-year quarter (March, June, September, and December).  If you change test method during the quarter, compare the counts for different testing to identify the appropriate response to the testing question.

Numerator Reporting for LabID Event: Transfer rule

The transfer rule does not apply to LabID Event reporting. LabID Events are attributed to the location of the patient at the time of specimen collection. The location of attribution for LabID Events is based on the inpatient location of the patient at time of specimen collection regardless of time spent or procedures performed in the location. There is 1 special case scenario available for use:  If a specimen collected in an affiliated outpatient clinic is positive for an MDRO or CDI, and the patient it is collected from is admitted to the facility on the SAME calendar date into an inpatient location that is monitoring LabID Events for the identified MDRO or CDI, the positive specimen can be reported as the first specimen for the patient in that admitting inpatient location for the month. If the facility is also monitoring outpatient LabID Events for the same MDRO or CDI in affiliated outpatient clinics (FacWideOUT), then the same specimen for the patient would also be reported a second time for that outpatient location.

Numerator Reporting for LabID Event: Discharged in past 4 weeks

The question is used to define a C. difficile LabID Event as community-onset healthcare facility-associated (CO-HCFA) (community onset event collected from a patient who was discharged from the same facility ≤4 weeks prior to the current date of stool specimen collection). The question refers to prior discharge from the same facility after an inpatient stay and offers meaningful information for appropriate event categorization. Discharge from an outpatient location (also known as an encounter) such as emergency department and 24-hour observation unit are not eligible for use.

Numerator Reporting for LabID Event: Prior evidence of infection

This is a non-editable data field and will auto-fill by the system based whether a MDRO LabID Event was submitted for the same MDRO and same patient in a prior month (not the current month) at this reporting facility. If there is a previous LabID event for this organism type identified by NHSN in a prior month, the system will auto-populate with a “YES.”  Note:  This data field is NOT used in the calculation of SIRs.

Instructions for completion of the LabID Event form can be found on the following site (must copy and paste the link): Instructions for completion of the LabID Event form [PDF – 100 KB].

Numerator Reporting for LabID Event: Admission date for inpatient rehabilitation facilities (IRF)

For NHSN purposes, if the IRF is located inside of the ACH:

  • Movement between the ACH and the IRF location is considered a location transfer and is treated as a single facility continuous stay (one admission and discharge).
  • The facility admission date for a LabID event should reflect the date the patient was physically admitted into either the inpatient location for the acute care hospital or the IRF location, whichever comes first during that patient’s stay.

Numerator Reporting for LabID Event: MRSA bacteremia, all specimen source

No. If monitoring all MRSA specimens, any MRSA isolate from the same patient and location after an initial report of MRSA during a calendar month is considered a duplicate MRSA isolate and should not be entered, except if it is a unique blood source.  If the first MRSA isolate for the month is from a blood source, no other non-blood MRSA isolates are reported for the calendar month for that patient and location.  If there is another positive MRSA blood isolate from same patient and location, there must be a full 14 days with no positive blood MRSA isolates for the patient and location before another MRSA Blood LabID Event is entered into NHSN for the patient.

See Figure 1 in MDRO and CDI Module (Chapter 12) [PDF – 3 MB] for algorithm for ALL SPECIMENS.

NHSN doesn’t encourage assumptions; the lab report must identify the isolate as ‘MRSA’ [or some form of the name] or have a susceptibility pattern which meets the definition to qualify for event reporting. MRSA includes S. aureus cultured from any specimen that tests oxacillin-resistant, cefoxitin-resistant, or methicillin-resistant by standard susceptibility testing methods, or any laboratory finding of MRSA (includes but not limited to PCR or other molecular based detection methods).

Distinguishing healthcare-associated infection (HAI) and LabID events

These are two very different CDI event reporting methods that are each governed by different sets of rules and date timeframes.


CDI LabID Event Reporting is based strictly on the number of hospital days between the specimen collection date and the date the patient is admitted to the facility.  Facility admission date is considered Day 1. There is no consideration for clinical presentation.

  • ≤ 3 days = community-onset (CO)
  • ≤ 3 days but patient had prior discharge from the reporting facility in the previous 4 weeks = community-onset healthcare facility-associated (CO-HCFA)
  • ≥ 4 days = healthcare facility-onset (HO)
  • GI-CDI HAI surveillance is based on specific infection criteria that are met within the HAI timeframe:


Day of admission or the day after = present on admission (POA) Hospital day 3 or greater = HAI

GI-CDI HAI surveillance based on specific infection criteria being met within timeframe

Each method requires a positive test for toxin-producing C. difficile on an unformed stool specimen.

Note:  Although diarrhea is not a specific element for a GI-CDI event, it must be checked when entering the GI-CDI event to validate that testing was performed on the appropriate specimen type.

Denominator Reporting for LabID Events: Outpatient encounter

NHSN defines an encounter as a patient visit to an outpatient location (ED, 24-hour observation) and is independent of admission to the inpatient facility.  Each encounter must be included in the total encounter count regardless of admission to the facility. Instructions for completion of denominator data for Infection Surveillance and/or LabID Events is found at (must copy and paste the link): http://www.cdc.gov/nhsn/forms/instr/57_127.pdf

Denominator Reporting for LabID Event: Facility count

Total Facility Patient Days/Admissions include all inpatient locations in the facility including units with separate CCNs such as inpatient rehabilitation facility (IRF) and inpatient psychiatric facility (IPF) locations.

Line 2 records the total facility counts minus counts from CMS-certified inpatient rehabilitation units (IRFs) and inpatient psychiatric units (IPFs) with a unique CCN. This is not a count of patients with an MDRO.

Line 3 records the total facility counts minus counts from CMS-certified inpatient rehabilitation units (IRFs) and inpatient psychiatric units (IPFs) with a unique CCN, and minus counts from all baby locations.  This is not a count of patients with CDI.


NOTE: Patient Days/Admissions on Line 2 and Line 3 of the FacWideIN form refer to the total number of patients housed in eligible inpatient locations (FACWIDEIN) in your facility, regardless of the patient’s MDRO or C. difficile infection status.

Step-by-step instructions for completing this information can be found in the Instructions for Completion of MDRO and CDI Prevention Process and Outcome Measures Monthly Monitoring form (CDC 57.127) [PDF – 61 KB].

Denominator Reporting for LabID Event: Report No Events

The ‘Report No Events’ box on the facility-wide inpatient (FacWideIN) form should be checked if there were no LabID events reported in any inpatient location, not including units with separate CCNs. If applicable, the ‘Report No Events’ box must be checked separately for each individual location, that is for, FacWideIN, emergency departments, 24-hour observation units, units with separate CCNs (such as an IRF), and other locations the facility has provided summary data.  For example, all LabID events for the month occur in the ED; you should check the ‘Report No Events’ box on the FacWideIN summary to indicate no inpatient events were submitted for the month.  Review events for each reporting month to determine in which location a LabID event was reported. Check the ‘Report No Events’ box as needed on the appropriate summary forms to complete reporting requirements.

For more information about resolving Alerts, refer to our Alert Guide: Alert Guide [PDF – 1 MB].

Categorizations: History of CDI

The First positive C. difficile specimen for the patient and the location is reported as a LabID event.  Once submitted, NHSN automatically applies a location level assignment of “CO” or “HO” based on the date of event.  An event occurring on HD 5 is categorized as a healthcare facility-onset (HO) CDI for the admitting facility [HO = specimen collection date was ≥ 4 days after inpatient admission to the facility]. The categorization is irrespective of testing performed prior to admission to a facility or patient history. LabID Event reporting and categorizations are based on a single reporting facility and for FacWideIN include inpatient, emergency department, and 24-hour observation locations in the reporting facility. The challenges of decreased specificity as it relates to true infection verses colonization is balanced by the intent of the categorizations used for LabID Events Reporting, which are:

  • Enabling the use of laboratory testing data without clinical evaluation of the patient.
  • Allowing for more effective standardization of reporting across all facilities.
  • Minimizing the burden data collection by the facilities and IPs .
  • Providing less subjectivity and being well-suited for public reporting.

Categorizations: Categories of the cdiAssay variable (Recurrent, incident, and blank)

These categorizations are based on the length of time between C. Difficile LabID Events for the same patient while in the same facility.  Specifically:

  • Incident CDI Assay: A CDI LabID Event from a specimen obtained >56 days after the most recent CDI LabID Event (or with no previous CDI LabID Event documented) for that patient.
  • Recurrent CDI Assay: A CDI LabID Event from a specimen obtained >14 days and ≤ 56 days after the most recent CDI LabID Event for that patient.
  • Recurrent CDI Assay: If CDI Assay appears missing, or blank, on the CDI Line List, this means that the specimen was obtained 14 days after the previous CDI LabID Event for this patient.

Locations: Swing beds & observation patients

All patients cared for / housed in an eligible inpatient unit should be included in counts (numerator and denominator) for FacWideIN LabID Event reporting, including patients designated as “swing bed” and “observation” status.

Analysis: SIR

  • MRSA Bacteremia: Events categorized as healthcare facility-onset (HO), non-duplicate and ‘Unique’ isolates from blood specimens are included in the numerator of the SIR.
  • difficile: Only HO incident events are included in the numerator of the SIR. Users can run a line list to determine which events are counted in the SIRs.

Data from IRFs and IPFs with separate CCNs are excluded from acute care hospitals’ FacWideIN LabID event SIRs.


The complete list of algorithms used to determine which events are counted in the SIR (for all facility types) can be found here: Troubleshooting the MRSA Bacteremia and CDI LabID Event SIR [PDF – 300 KB].

Analysis: Line listing, indicator variable

The MRSA bacteremia and CDI LabID Event Line Lists contain indicator variables that identify which events are counted in the SIR. The indicator variables for acute care hospitals are listed below [Facility wide incidence SIR= Facility wide Inpatient (FacWideIN) SIR:

  • Facility-wide incidence (SIR) for MRSA bacteremia: FWMRSA_bldIncCount
  • Facility-wide incidence (SIR) for difficile: FWCDIF_facIncHOCount

Variable will display as 1 or 0 for each event:

  • 1: event is counted in the SIR
  • 0: event is NOT counted in the SIR

NOTE: separate indicator variables are available for CMS-certified IRF units. Refer to the Troubleshooting Guide: Troubleshooting Guide [PDF – 300 KB].

Analysis: Line listing, categorizations of MRSA bacteremia LabID Events

To show risk at the location/unit level where the patient has been housed, all location/unit level LabID events reported into the NHSN application will appear on the line list.  However, the categorizations assigned (HO vs. CO) on the line list are based only on the patient’s facility admission date and specimen collection date.

This means that although the first reported LabID Event is categorized as CO if the specimen is collected fewer than four days after inpatient admission, a subsequent LabID Event submitted to NHSN for the same patient, but a different location will be categorized as HO if the specimen is collected on Day 4 or later after inpatient admission to the facility. Each LabID event is viewed independently of other events at this level.

Note: For FacWideIN reporting, however, duplicate LabID Events will be removed during analysis. Your SIR report will provide a more accurate description of your FacWideIN numbers.

CMS Inpatient Quality Reporting (IQR) Program for Acute Care Hospitals (ACH): CMS reporting requirements & data submitted

CMS guidance documents and reporting requirements can be found on the NHSN home page under “CMS Requirements” (must copy and paste the link):  CMS guidance documents and reporting requirements [PDF – 245 KB].

FacWideIN standardized infection ratios (SIRs) are sent to CMS for those hospitals participating in the Hospital Inpatient Quality Reporting program.  The numerator of the SIR is a count of the following events:

  • Healthcare facility-onset (HO) MRSA bacteremia LabID Events (Unique blood events)
  • HO CDI LabID Events (incident cases).

Additional data such as community-onset events and monthly denominators are incorporated into the SIR calculations that are submitted to CMS. To ensure complete reporting of MRSA and CDI, refer to this document: How to Set Up Facility-Wide Inpatient MRSA Bacteremia and C. difficile LabID Event Reporting [PDF – 300 KB].

NOTE: Duplicate LabID Events reported at the location level are excluded from SIR calculations. For more information about the algorithms used to determine which events are counted in the SIR, refer to our LabID Troubleshooting Guide: LabID Troubleshooting Guide [PDF – 250 KB].