Reporting MDRO and C. difficile LabID Events to NHSN: Common Questions

CDC's National Healthcare Safety Network (NHSN) is the most widely used system in the country for tracking healthcare-associated infections. Facilities report multidrug-resistant organisms (MDROs) and Clostridioides difficile infection (CDI) to it as LabID events — events identified from laboratory results alone. These answers to common questions come from NHSN's FAQ; the full rules are in the MDRO/CDI protocol.

Which lab results count as a CDI LabID event

What counts. A CDI LabID event is either:

• a positive test for C. difficile toxin A and/or toxin B, or
• any detection of toxin-producing C. difficile by culture or other lab method,

on an unformed stool specimen that takes the shape of its container. Methods include, among others, molecular assays such as PCR and toxin assays such as EIA.

Antigen results don't count, positive or negative. Only toxin results can define a CDI LabID event.

Multi-step testing. When several tests are run on the same unformed stool specimen, the result of the last test performed decides whether the event is reported — whatever the method or order. You can only tell which test came last if the final lab report gives a time for each test. Without separate time stamps, treat the tests as simultaneous: any positive toxin result can be used. The MDRO protocol includes examples of algorithms and how to read them.

Collection method doesn't matter. Any unformed stool positive for toxin A and/or B qualifies, including stool from an ostomy, and whether or not the stool's usual consistency or amount has changed. This keeps LabID reporting simple — no need to gather information beyond the collection and admission dates — and removes subjectivity. A specimen labeled as anything other than "stool" is not eligible.

The standard testing method (quarterly question)

Each quarter the facility reports the testing method its lab (or its outside lab) uses most often for C. difficile. Answer with the method used routinely, in the last month of each quarter (March, June, September and December). If the method changed during the quarter, choose the one used for most of the quarter.

Where an event is attributed

• The transfer rule does not apply to LabID events. An event belongs to the patient's inpatient location when the specimen was collected, regardless of how long they were there or what was done there.
• One special case: if a specimen collected in an affiliated outpatient clinic is positive, and the patient is admitted the same calendar day to an inpatient location that is monitoring that MDRO or CDI, the specimen may be reported as that patient's first specimen of the month in the admitting location. (Emergency departments and 24-hour observation units, which count in facility-wide inpatient reporting, are not "affiliated outpatient clinics.") If the facility is also monitoring outpatient LabID events in its clinics (FacWideOUT), the same specimen is reported a second time for the outpatient location.

Questions on the event form

"Discharged from your facility in the last 4 weeks?" This answer is needed to classify a C. difficile event as community-onset healthcare facility-associated (CO-HCFA): a community-onset event in a patient discharged from the same facility no more than 4 weeks before the stool was collected. It refers only to discharge after an inpatient stay; outpatient encounters (ED, 24-hour observation) don't count.

"Documented evidence of previous infection or colonization…?" This field can't be edited. The system fills in "Yes" automatically if a LabID event for the same MDRO and same patient was submitted at the facility in a prior month (not the current one). It isn't used in calculating SIRs.

Inpatient rehabilitation inside a hospital. If an inpatient rehabilitation facility (IRF) is located inside an acute care hospital, moving between them is a location transfer within one continuous stay (one admission, one discharge). The admission date is when the patient was first physically admitted to either location, whichever came first.

Repeat MRSA bacteremia without new susceptibility results. NHSN doesn't encourage assumptions. To be reported, the lab report must name the isolate as MRSA (in some form) or give a susceptibility pattern that meets the definition — even if the lab's own standard skips repeat testing within 72 hours and says "refer to previous susceptibility." MRSA means S. aureus from any specimen that tests oxacillin-, cefoxitin- or methicillin-resistant by standard methods, or any lab finding of MRSA, including PCR and other molecular methods.

LabID events vs. HAI GI-CDI cases

These are two separate reporting methods with different rules and timeframes. Both require a positive test for toxin-producing C. difficile on an unformed stool specimen.

How GI-CDI HAI surveillance applies its timeframe. Image from CDC's page.

Diarrhea isn't a specific criterion for a GI-CDI event, but it must be checked when entering one, to confirm the test was done on the right specimen type.

Denominators

Encounters. An encounter is a patient visit to an outpatient location (ED, 24-hour observation), counted separately from any inpatient admission. Every encounter goes into the total, whether or not the patient was admitted.

Facility counts on the FacWideIN form:

Lines 2 and 3 cover all patients in eligible inpatient locations, whatever their MDRO or C. difficile status.

The "Report No Events" alert. Check "Report No Events" on the facility-wide inpatient form when no LabID events were reported in any inpatient location (excluding separate-CCN units). The box must be checked separately for each kind of location with summary data — FacWideIN, emergency departments, 24-hour observation units, separate-CCN units such as an IRF, and so on. So if all of a month's events were in the ED, check "Report No Events" on the FacWideIN summary to show no inpatient events were submitted. NHSN's Alert Guide explains how to resolve alerts.

Categorising events

Onset. NHSN assigns community onset (CO) or healthcare facility onset (HO) from two dates only — facility admission and specimen collection. Specimens from outpatient locations, and inpatient specimens on hospital days 1–3, are CO; inpatient specimens on day 4 or later are HO. So a patient with a history of CDI, admitted without symptoms, who develops diarrhoea and tests positive on hospital day 5 is reported as a LabID event and categorised HO, whatever the earlier history or testing. The approach trades some specificity (infection versus colonisation) for laboratory-only reporting, standard reporting across facilities, less work for infection preventionists, and objective data suited to public reporting.

Each event stands alone at the location level. A second MRSA bacteremia event from a different inpatient location within 14 days can be HO even though the first was CO; duplicate LabID events are removed when FacWideIN data are analysed.

Incident or recurrent CDI — by time since the patient's last CDI LabID event in the same facility:

Swing-bed and observation patients housed in an eligible inpatient unit are counted, numerator and denominator, in FacWideIN reporting.

What counts in the SIR

• MRSA bacteremia: healthcare facility-onset, non-duplicate, unique blood isolates.
• C. difficile: healthcare facility-onset incident events only.
• Data from IRFs and IPFs with their own CCNs are excluded from an acute care hospital's FacWideIN SIRs.
• On the line lists, indicator variables show whether each event counts (1) or not (0): FWMRSA_bldIncCount for MRSA bacteremia and FWCDIF_facIncHOCount for C. difficile; CMS-certified IRF units have their own. NHSN's LabID troubleshooting guide sets out the full algorithms.

CMS reporting. For hospitals in CMS's Hospital Inpatient Quality Reporting program, NHSN sends FacWideIN SIRs to CMS; their numerators count HO MRSA bacteremia (unique blood) events and HO incident CDI events, with community-onset events and monthly denominators used in the calculation. CMS's requirements are linked from the NHSN home page.

Sources

Based on "FAQs: Multidrug-Resistant Organism & Clostridioides difficile Infection (MDRO & CDI)," National Healthcare Safety Network, Centers for Disease Control and Prevention; a work of the United States government in the public domain. Questions 14 to 20 — categorisations, the SIR and CMS reporting — were missing from the imported page and are taken from the page as published.