Hospital-onset bacteremia (HOB) counts a blood culture that grows a bacterial or fungal organism on or after the fourth day of an inpatient stay, wherever the infection started. Central line-associated bloodstream infection (CLABSI) counts only bloodstream infections that meet NHSN criteria for a central line source. HOB isn't part of any CMS payment program yet. CDC's National Healthcare Safety Network (NHSN) released its first HOB surveillance protocol in 2026, though, and the Society for Healthcare Epidemiology of America (SHEA) has asked CMS to add HOB to the Hospital-Acquired Condition (HAC) Reduction Program.
What changes for most hospitals is how much gets counted. Published studies find about four HOB events for every CLABSI, and most of them come from sources no current CMS infection measure tracks.
What is hospital-onset bacteremia?
Under the 2026 NHSN Bacteremia and Fungemia Surveillance Module protocol, an HOB event is a bacterial or fungal organism identified from a blood culture collected on the fourth calendar day of an inpatient stay or later. Day 1 is the date the patient physically arrives on an inpatient unit, not the date of ED arrival or the admission order.
Several exclusions keep the count from becoming every positive culture collected after day 3:
Organisms on NHSN's bacterial skin commensal list, such as Staphylococcus epidermidis, are excluded.
A culture is excluded if any organism in it matches one already identified earlier in the same stay, whether in the ED, in observation, or on inpatient days 1 through 3.
Each hospital stay can have only one HOB event. Positive cultures in the next 14 days are added to that event, and positive cultures after that window are not counted.
Nobody attributes a device or reviews the chart. NHSN applies the logic itself to EHR data the hospital sends electronically, and the module won't accept manual entry.
Is HOB replacing CLABSI?
No, not as of October 2026. CLABSI is still one of five NHSN measures in the CMS HAC Reduction Program, along with CAUTI, colon and abdominal hysterectomy SSI, MRSA bacteremia, and C. difficile infection. CMS left the program unchanged in its FY 2027 inpatient final rule, issued July 31, 2026.
What SHEA has actually recommended is an addition. In its comments on the FY 2026 inpatient rule, SHEA asked CMS to bring HOB and hospital-onset antibiotic-treated C. difficile infection (HT-CDI) into the HAC Reduction Program as new NHSN measures. Researchers have modeled what would happen if HOB replaced the current measures, but no CMS proposal has gone there.
The overlap is also smaller than most people assume. HOB excludes skin commensals, so a CLABSI caused by coagulase-negative staphylococci may never show up as an HOB event. In a 41-hospital study by Yu and colleagues, 30% of NHSN-reported CLABSIs grew only commensal organisms that fell outside the study's HOB definition.
How much bigger is HOB than CLABSI?
Across the U.S. studies published so far, the ratio comes out at roughly four HOB events for every CLABSI, and most of the extra events are not already captured by another current CMS infection measure.
41 hospitals, 2015–2019. Yu and colleagues found 1,574 patients with HOB that was not a CLABSI, compared with 403 patients with an NHSN-reported CLABSI, about four to one (Infection Control & Hospital Epidemiology, 2023).
One large academic medical center, 2022–2024. Among 427 patients with HOB at UC Irvine, 24% met NHSN CLABSI criteria, 5% met SSI criteria, and fewer than 1% met CAUTI criteria, leaving roughly 70% of HOB patients outside all three definitions (Gohil et al., IDWeek 2025 abstract).
A 500-bed safety-net hospital, 2022–2023. At Denver Health, 55% of infections were identified only by HOB, 21% by both HOB and a CMS-reportable measure, and 25% only by a CMS measure (Young et al., IDWeek 2025 abstract).
The Denver result may be the one to drive your planning. HOB reaches further than the current measure set without containing it. CAUTIs and SSIs that never seed the bloodstream drop out, while bacteremias from abdominal, respiratory, urinary, and peripheral line sources show up for the first time.
These aren't low-stakes infections, and many can likely be prevented. In the Yu study's matched analysis, non-CLABSI HOB was associated with 13.8 more hospital days and $35,310 more per admission than controls, not far behind CLABSI at 16.8 days and $49,400. A 13-hospital review led by Leekha and colleagues rated 36% of non-commensal HOB events potentially preventable, and about 40% of those preventable events would have been missed by existing HAI surveillance. We look at what else sits behind numbers like these in The True Cost of an Infection.
Where does HOB stand right now?
As of October 2026, HOB has a published protocol and a working NHSN module, but access is limited to pilot sites and no CMS payment depends on it.
Timeline:
Early 2023 - The HOB measure passes National Quality Forum Patient Safety Committee review (Yu et al.)
June 2025 - SHEA recommends that CMS add HOB and HT-CDI to the HAC Reduction Program
January 2026 - NHSN releases version 1 of the Bacteremia and Fungemia Surveillance Module protocol, labeled provisional
March 2026 - NHSN annual training describes the module as a pilot release to selected NHSNCoLab sites
July 31, 2026 - CMS issues the FY 2027 inpatient final rule with no changes to the HAC Reduction Program
A few details of how the module works will shape your preparation:
Reporting is electronic only. Hospitals send EHR data in the HL7 FHIR R4 standard, and NHSN determines events centrally. The module does not accept manual entry or CDA files.
The measure is a risk-adjusted standardized infection ratio (SIR). NHSN's measure page describes an annual HOB SIR. Module reports also show crude risk per 100 eligible stays and incidence density per 10,000 eligible patient days.
Eligibility is wide on paper. The protocol lists all NHSN-enrolled inpatient facilities as eligible, including critical access, children's, long-term acute care, and inpatient rehabilitation hospitals. NHSN's module page still describes access as limited to select hospitals.
CDC also plans to add an adult blood culture contamination rate in a future version of the module. Skin commensal contamination doesn't create HOB events now, but it will be measured on its own.
CMS's next chance to propose HOB is the FY 2028 inpatient proposed rule, usually released in April. We'll update this post when it comes out.
How should a facility prepare for HOB?
Sooner or later, someone on your quality committee will see an HOB rate next to last year's CLABSI rate and ask why bloodstream infections quadrupled. They didn't. The measure got wider, and that conversation will go much better if you prepare in advance and communicate your own baseline before the first NHSN report shows up.
Build a baseline from your microbiology data. Pull 12 to 24 months of positive blood cultures and run the protocol logic against them: inpatient day 4 or later, skin commensals removed, cultures matching an earlier organism in the same stay removed, one event per stay with a 14-day window. Count days from when the patient physically reached the inpatient unit. Use ADT timestamps rather than the admission order, because this is where homegrown baselines drift, especially in hospitals with long ED boarding times. Then set your HOB count beside your CLABSI count for the same months. If more than one person applies the logic, check that they agree before trusting the result; we test our own infection preventionists on that kind of agreement every year.
Review a sample of events for source. HOB doesn't assign a source, but prevention will still needs one to determine the best approach for intervention. In the Yu study, 32% of patients with non-CLABSI HOB had the same organism in another culture, usually urine or a respiratory specimen. If your sample looks like that, the work reaches past central line bundles to urinary catheters and non-catheter UTIs, ventilated and non-ventilated pneumonia, abdominal sources, and peripheral IVs. The National Quality Forum's Hospital-Onset Bacteremia and Fungemia Playbook includes a root cause framework you can adapt.
Talk to IT now. The module only takes electronic FHIR submissions, so HOB accuracy rides on mappings most infection preventionists never see: lab tests to LOINC, organisms and specimens to SNOMED, medications to RxNorm, and locations to NHSN location codes. One mis-mapped unit or a wrong admission timestamp can move an event between community onset and hospital onset.
Look at blood culture ordering. HOB counts what gets cultured, and NHSN tracks hospital-onset test intensity next to the measure. Over-culturing will turn up more events. Under-culturing will hide real infections. A culture contaminated with S. epidermidis won't count, but one contaminated with S. aureus will, so collection technique needs to be a part of the plan too. It's the same diagnostic stewardship reasoning behind C. difficile testing stewardship, applied to a different test.
Getting help with an HOB baseline
IP&MA's Surveillance Support team works with hospitals on NHSN surveillance accuracy, the problem behind The Hidden Costs of Surveillance Variability. For HOB, we can build a protocol-matched baseline from your lab and ADT data, review a sample of events for likely source, and show where prevention work will move the number. Schedule a discovery call to see what your data looks like under HOB.