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

Numerator Reporting for LabID Events: Definition of CDI Assay

Q1: When reporting CDI LabID, what lab result should be reported as an event?

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, *No Toxin detected) 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

Q2: Our facility uses a multi-step process to test for C. difficile toxins, should we report an event if the screening test is positive and the confirmatory test is negative or the opposite (screening test is negative and confirmatory test is positive)?

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 pdf icon[PDF – 2 MB].


Numerator Reporting for LabID Events: Acceptable specimens for CDI reporting

Q3: Are specimens collected from colostomy bags considered acceptable for C. difficile LabID event 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

Q4: Our facility uses a combination of test methods for C. difficile LabID event reporting, how should we answer the question: For this quarter, what is the primary testing method for C. difficile used most often by your facility’s laboratory or the outside laboratory where your facility’s testing is performed?

The response should reflect the testing method used with the majority of specimens tested.  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.  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 the testing 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

Q5: How does the transfer rule apply to the patient at the time of discharge for FacWideIN?

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

Q6: Why is the question, “Has the patient been discharged from your facility in the last 4 weeks?” required for answer?

The question is used to define a LabID Event as community-onset healthcare facility-associated (CO-HCFA) (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 an emergency department and 24-hour observation unit are not eligible for use.


Numerator Reporting for LabID Event: Prior evidence of infection

Q7: Why will the system not let me answer “Yes” to the question “Documented evidence of previous infection or colonization with this specific organism type from a previously reported LabID Event in any prior month?”

This is a non-editable data field and will auto-fill by the system based on 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 entered into 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 (57.128) pdf icon[PDF – 100 KB].


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

Q8: What admission and discharge date should be entered when the patient is admitted into an IRF that is located inside of an acute care hospital (ACH)?

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

Q9: When following All Specimen sources for MRSA LabID Event reporting, if a MRSA blood isolate is entered as the first specimen of the month, can a second MRSA non-blood specimen (for example, urine) be entered that month for the same patient and same location?

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 icon[PDF – 3 MB] for algorithm for ALL SPECIMENS.

Based on the lab standard our facility follows, sensitivity testing is not required for the same organism if tested within previous 72 hours. Are we required to report a repeat MRSA bacteremia if a result in that timeframe comes back “refer to previous susceptibility.”  Do we assume the specimen is MRSA if we do not have sensitivity on that specific isolate?

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

Q10. How does determining a HAI GI-CDI case differ from a CDI LabID event?

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 event to validate that testing was performed on the appropriate specimen type.


Denominator Reporting for LabID Events: Outpatient encounter

Q11: Define 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: MDRO and CDI Monthly Denominator Form (CDC 57.127) pdf icon[PDF – 150 KB].


Denominator Reporting for LabID Event: Facility count

Q12. What is the difference between Total Facility Counts (admissions and patient days) reported on Line 1 and the counts (patient days and admissions) on Line 2 and Line 3?

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 icon[PDF – 61 KB].


Denominator Reporting for LabID Event: Report No Events

Q13. Why do I get an Alert to check the ‘Report No Events’ box on the FacWideIN summary form when I know my facility reported at least one LabID event for this month and location?

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 for each individual location, that is for, FacWideIN, emergency departments, 24-hour observation units, units with separate CCNs, and other locations the facility has provided summary data. Review the events for that month to determine in which location the LabID event was reported, and check the ‘Report No Events’ box as needed on the appropriate summary forms.

For example, if a single LabID event reported for a month was from the emergency department (ED), then the ‘Report No Events’ box on the FacWideIN summary form should be checked for that month.

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


Categorizations: History of CDI

Q14: If a patient with a history of CDI is admitted without symptoms, but on Hospital Day 5 has diarrhea and test positive for C. difficile – should a CDI LabID Event be reported? How is the event categorized?

The First positive C. difficile specimen for the patient and the location is reported as a LabID event. NHSN will categorize it as a healthcare facility-onset (HO) CDI for the admitting facility if the 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. 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)

Q15: Please define recurrent and incident C. difficile.

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.
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

Q16: Should patients in a swing bed and/or observation status be included in FacWideIN inpatient reporting?

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

Q17: Which MRSA and C. difficile LabID Events are included in the standardized infection ratio (SIR) for my acute care hospital?

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.
C. 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 icon[PDF – 300 KB].


Analysis: Line listing, indicator variable

Q18: How do I know which MRSA bacteremia and CDI LabID Events are counted in the SIR when looking at the line listing?

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 C. 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 pdf icon[PDF – 300 KB].


Analysis: Line listing, categorizations of MRSA bacteremia LabID Events

Q19: If the first MRSA bacteremia LabID event appears on the line listing as a community-onset (CO) event, why does a second MRSA bacteremia LabID Event collected within 14 days from a different inpatient location in the facility get categorized as healthcare-facility onset (HO)?

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 entered into 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

Q20: Where are CMS reporting requirements found and what facility data are being submitted to CMS for FacWideIN MRSA bacteremia and C. difficile LabID Events?

CMS guidance documents and reporting requirements pdf icon[PDF – 245 KB] can be found on the NHSN home page under “CMS Requirements”.

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 icon[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 pdf icon[PDF – 250 KB].