NHSN Bloodstream Infection FAQs: CLABSI, Secondary BSI and Central Line Rules

About these answers

These are CDC National Healthcare Safety Network (NHSN) answers to frequent questions about bloodstream infection (BSI) surveillance: laboratory-confirmed bloodstream infections (LCBI) and central line–associated bloodstream infections (CLABSI). The full rules are in the NHSN BSI protocol (Chapter 4), Chapter 2, Identifying HAIs, and Chapter 17's site-specific definitions.

Primary or secondary?

When is a BSI secondary? Only after the patient fully meets an NHSN site-specific infection definition — Chapter 17, or the PNEU, UTI or SSI protocols — and then only in two scenarios (Appendix B, the Secondary BSI Guide):

1. the blood and the site-specific specimen share at least one matching organism, and the blood was collected within the site's secondary BSI attribution period (SBAP); or
2. the blood specimen is itself an element of the site-specific criterion, collected within its infection window period (IWP).

A BSI can also be secondary to a ventilator-associated event (VAE) under the VAE protocol. If none of this applies, report a primary LCBI — and a CLABSI if an eligible central line was in place on the date of event or the day before. Table B-1 lists which definitions need a matching organism and which use blood as an element.

Ventilated adults under VAE surveillance: a BSI can't be secondary to a VAC or IVAC. It can be secondary to PVAP if the blood organism matches a respiratory specimen used to meet PVAP and the blood was drawn within the 14-day VAE period. Otherwise, check the other site definitions; failing those, it may be a primary BSI/CLABSI.

Pneumonia: a BSI can't be secondary to PNU1. But if a blood culture falls outside PNU1's window, or doesn't match the organism used for PNU2 or PNU3, check whether PNU2 can be met again within the PNEU repeat infection timeframe (RIT). Re-meeting PNEU within the RIT needs only one definitive imaging test in the new window showing the prior findings persist.

An example of a pneumonia event's timeframes. CDC.

GI and intra-abdominal infection on pathology (GIT 1b, IAB 2b): the blood organism must be an MBI organism, the histopathology and blood must fall in the IWP, and the organisms must match — for example, Candida budding hyphae in an intestinal ulcer and Candida albicans in blood two days later.

Non-matching organisms: an organism that doesn't match can ride along in the SBAP only if it's in the same blood specimen as a matching one and is eligible for that site's criteria. E. coli urine with E. coli plus Enterococcus faecalis in blood: both captured. A later blood culture with E. faecalis alone: not secondary. Candida with E. coli: Candida isn't eligible for urinary criteria, so it isn't captured.

Mucosal barrier injury (MBI-LCBI)

• MBI-LCBI or secondary? MBI-LCBI captures BSIs thought to come from a weakened immune system and gut changes. When GI symptoms are present, use clinical judgment and the record: if there's an infectious process in the gut and a Chapter 17 GI criterion is met, the BSI may be secondary.
• In national data? Since the 2015 re-baseline, MBI-LCBIs are not in CLABSI metrics or files shared with CMS, but facilities under CLABSI surveillance must still report them.
• MBI RIT exception: an MBI-LCBI stays MBI-LCBI if a non-MBI positive culture is collected during its RIT and can be deemed secondary to a site-specific infection.

Timing rules

• Repeat infection timeframe: a 14-day period, starting on a primary BSI's date of event, during which no new BSI is reported; new organisms are added to the first event. A CLABSI on hospital day 12 means the next possible new BSI is day 26. Only primary BSIs create a BSI RIT; a secondary BSI doesn't, so later positives may need their own investigation.
• Device status is fixed: if the first BSI (day 4) had no central line and a line placed on day 5 is followed by a positive culture on day 8, the event does not become a CLABSI — device association, date of event and location never change within a RIT.
• Commensal date of event: two matching common-commensal cultures count as one element. If symptoms come first within the IWP, the date of event is the first symptom's date; otherwise it follows the first blood specimen.

Blood cultures

• Draw site doesn't matter: a positive central-line culture meets CLABSI criteria even if a simultaneous venipuncture culture is negative.
• "Separate occasions": for common commensals (LCBI 2 or 3), at least two blood draws on the same or consecutive calendar days.
• Matching commensals: Staphylococcus capitis and S. auricularis are both coagulase-negative staphylococci but, named to species, don't match. Reported only as "coagulase-negative Staphylococcus," they would.
• Catheter tips aren't used: tip cultures are contaminated more often than blood cultures, and not all labs can quantify them. (They belong to the clinical definition of catheter-related BSI; see the 2011 Guidelines for the Prevention of Intravascular Catheter-Related Infections.)
• Non-culture tests (NCT) can meet LCBI-1 — unless blood was cultured within 2 days before or 1 day after, in which case the culture decides. They can't meet LCBI-2 or LCBI-3, which need matching cultured organisms plus signs and symptoms.
• Vital signs (hypotension, apnea, bradycardia): NHSN sets no values; use your facility's own parameters.

Which lines count

• Counting days: all central lines — permanent, temporary, implanted ports, umbilical — are treated alike. Lines present on admission count as central line days from the day of admission, even if not accessed. A patient admitted January 1st whose line is first accessed on the 4th, with a BSI on the 6th, contributes 6 line days.
• Eligibility for CLABSI: a line must first be accessed — placed, or used for infusion, blood draws or hemodynamic monitoring — in an inpatient location and be in place more than 2 consecutive calendar days; it becomes eligible on line day 3 after access. A port already infusing when the patient arrives counts from arrival; one not accessed until later counts from that access. A line never accessed is never eligible, but still counts in the denominator.
• Removal and reinsertion: any part of a calendar day with a line counts; a full day without one restarts the count.
• Two lines at once: no need to pick one; just record whether an eligible line was present. Count one line day per patient per day; in oncology units with a temporary and a permanent line, report the temporary one.
• Not central lines: midline catheters (unless the tip actually lies in a great vessel and the line is used as a central line), intra-aortic balloon pumps (not used for infusion or monitoring, and not ventricular assist devices), and femoral arterial lines (the femoral artery isn't a great vessel).

Where to attribute

• Dialysis: a CLABSI in an inpatient dialyzed by dialysis staff, in the room or the dialysis unit, belongs to the inpatient location where the patient is housed — even if unit nurses never touch the dialysis catheter. Facilities answer for care by contracted staff too.
• Locations for CMS reporting: see the operational guidance for acute care hospitals; CMS is the final authority.
• Case help: the NHSN Helpdesk can help decide primary versus secondary if sent the case details, starting with the admission date.

Exclusions

These must still be reported, but don't count as central line–associated or toward the CLABSI SIR:

• extracorporeal life support, such as ECMO;
• epidermolysis bullosa;
• Munchausen syndrome by proxy;
• pus at another vascular access site with a matching organism — mark "pus at the vascular access site" and "Central line" as Yes (the device list includes arterial catheters outside the pulmonary artery, aorta or umbilical artery, arteriovenous fistulae and grafts, atrial catheters, HERO dialysis catheters, IABPs, non-accessed central lines, peripheral IVs, and midlines that don't meet the central line definition);
• patient self-injection: observed or suspected injection by the patient into their own line during the IWP (not by staff, family or visitors). These remain LCBIs and create a RIT; answer Yes to both "central line" and "self-injection";
• total artificial heart;
• ventricular assist device.

Sources

Based on "FAQs: Bloodstream Infection (BSI) Events," National Healthcare Safety Network, Centers for Disease Control and Prevention; a work of the United States government in the public domain. See also the VAE FAQs.