Most Spine Surgery Infections Come From Patients’ Own Skin

86% of surgical site infections after instrumented spine surgery matched bacteria the patient already carried, a University of Washington team found. The work tracked 14 infections among 204 people whose operations placed hardware in the spine.

Those infections still get filed as healthcare-associated events. The usual preventive shot is still cefazolin, a drug that failed against most of the isolates in the study.

Fourteen Spine Infections, Mapped Strain by Strain

The paper appeared on April 10, 2024, in Science Translational Medicine (Vol. 16, Issue 742). Lead author Dr. Dustin Long, an anesthesiologist and critical-care physician at Harborview Medical Center, and colleagues used instrumented spine surgery as a model of a clean, class I skin incision.

They sampled skin, nose, and rectum before the first cut, then compared those communities with bacteria grown later from infected wounds. The method was genomic matching of preoperative strains with the bugs recovered after surgery, not a guess based on species names.

Surgical site infection developed in 14 of 204 enrolled patients, or 6.8% in this series. That is higher than the rough figure of about 1 in 30 operations that Long cited from Agency for Healthcare Research and Quality material, and the gap fits a cohort built on hardware cases rather than all clean surgery.

THE HARBORVIEW SPINE COHORT

Among a superset of 1,610 patients, the team found no common-source outbreak and no sign that one person’s pathogen had hopped to another. A companion commentary in the same issue said the results question how much further gains will come from tighter sterility and broader antibiotic coverage.

Hospital Scorecards Still Count These as Acquired

Long told UW Medicine that infection now plays an oversized role in surgical outcomes and is heavily weighted in quality measures used for public reporting and insurance reimbursement. The federal machinery still talks about these events as hospital-acquired conditions even when the strain was on the skin before admission.

Medicare’s Hospital-Acquired Condition Reduction Program does not score spine surgery infection. It scores surgical site infection after colon surgery and abdominal hysterectomy, then folds those ratios into a composite with other harm measures. Hospitals in the worst-performing quartile take a 1 percent Medicare payment cut on fee-for-service discharges for the year, a flat penalty rather than a sliding scale.

HOW FEDERAL INFECTION SCORES WORK

• The penalty: A Total HAC Score above the 75th percentile triggers a 1 percent cut on overall Medicare fee-for-service payments.
• The SSI slice: The program’s surgical site infection measures are colon surgery and abdominal hysterectomy, not spine.
• Colon surgery in 2024: CDC’s 2024 national HAI progress report showed a 4% decrease in colon surgery SSIs versus 2023.
• Hysterectomy in 2024: Abdominal hysterectomy SSIs rose 8% over the same span.

The American College of Surgeons National Surgical Quality Improvement Program still treats surgical site infection, including superficial, deep, and organ-space events, as one of eight outcome areas when it names meritorious hospitals. Leapfrog’s hospital survey pulls SSI after colon surgery through the CDC’s National Healthcare Safety Network. None of those scoreboards ask whether the strain was sitting on the patient at home.

Surgical site infections account for 20% to 31% of hospital-acquired infections in a 2024 analysis in The Joint Commission Journal on Quality and Patient Safety. That paper put extra medical costs at $20,000 or more for the stay and put annual U.S. spending on these infections between $3.3 and $10 billion. The dollars are real. The label “hospital-acquired” is doing work the Harborview genomes do not support for this operation.

Cefazolin and the Standard Preventive Shot

American Society of Health-System Pharmacists therapeutic guidelines recommend cefazolin for spinal procedures with and without instrumentation, with a strength-of-evidence grade of A. The same tables hold clindamycin or vancomycin for patients with a beta-lactam allergy. Second- and third-generation cephalosporins, the guidelines say, offer no major advantage.

That is a population protocol. It assumes the typical wound threat is a staph species that cefazolin can reach. In the Harborview series, 59% of surgical site infection isolates were already resistant to the preventive antibiotic given in the room, and that resistance lined up with resistance genes in the patient’s preoperative bacterial mix (p=0.0002).

THE STANDARD PREVENTIVE SHOT

• First-line drug: Cefazolin for spine operations with and without hardware.
• Adult dose: 2 grams, or 3 grams if the patient weighs more than 120 kilograms.
• Timing: Start within 60 minutes before incision, with redosing on long cases.
• Allergy path: Clindamycin or vancomycin when a beta-lactam cannot be used.
• After closure: Extra doses are not recommended as a routine way to cut infection risk.

A 2026 analysis of elective spine procedures still treated cefazolin as first-line and compared it with vancomycin. The live argument in that literature is which standard drug to open, not whether to pick a drug from the bacteria a named patient already carries.

The Bacteria on the Back Follow a Map

The team could place bugs on the body before anyone draped the field. Staphylococci ran denser on the neck and upper back, the same neighborhood as nasal colonizers. Bacteria such as E. coli showed up more often on the lower back, in line with gut and stool flora.

Dr. John Lynch, medical director of Harborview’s Infection Prevention and Control Program and a coauthor, said the group had never had a map like this of how skin bacteria play a role in a surgical site infection. Infection after surgery on a given stretch of spine tracked the bugs that already lived on that stretch of skin.

That pattern is hard to blame on a dirty lamp or a shared instrument. A hospital strain hopping from bed to bed would not sort itself so neatly into neck flora versus lumbar flora. The genomes did not show that hop. The map did show why a single intravenous drug, chosen for the average staph, can miss a gut organism waiting on the lower back.

What a Pre-Surgery Swab Would Change

A swab of skin, nose, and stool before incision would show which bacteria a patient already carries and which drugs those strains can shrug off, so the preventive antibiotic could be chosen for that person instead of defaulting to cefazolin. That is the prevention model the authors want, and it is not how spine rooms are run.

Dr. Stephen Salipante, a clinical pathologist, director of UW Medicine’s Microbial Interactions & Microbiome Center sequencing services, and a senior author, said the work extends personalized medicine to a patient’s own bacterial community. Lynch put it in practical terms: act at the individual level based on specific bacteria or the level of the spine being opened.

If you look at where we currently focus our efforts and a lot of the guidelines and commercial products that are out there, it’s very focused on the sterility of the hospital environment. It’s certainly not patient-centered or individualized in any meaningful way.

Dr. Dustin Long, anesthesiologist and critical-care physician, Harborview Medical Center, to UW Medicine

Long also said the field still lacks basic science, for many operations, on where the infections come from, how they enter the wound, and how they get around the usual stops. He compared a 1-in-30 failure rate with a production line in which one unit in 30 blew up with no explanation. Avoiding infection 97% of the time, he said, can sound acceptable until that one patient is yours.

Screening every spine patient, sequencing what grows, and stocking a wider preventive shelf would cost time and money the paper does not price. It would also mean treating the person on the table as the main reservoir, which is a different job from wiping the room again.

The Authors Do Not Let Hospitals Off

Long said the authorship team wrote into the paper that it does not see the results as not an out for hospitals. The findings, he said, should push teams to protect patients from themselves when they enter the vulnerable state of surgery.

That line matters because the public fight over surgical site infection has been a fight about the building. Report cards, reimbursement cuts, and commercial sterility products all point at the operating room. The Harborview genomes point at the skin the patient walked in with, and at a preventive drug that already could not cover most of the isolates that later caused trouble.

The study is one operation, in one system, with 14 infections. It does not rewrite colon surgery or trauma care. It does show, with strain-level matches, that a clean spine case can fail because of bacteria that never needed a hospital to exist. Two years of later spine literature still opened with cefazolin versus vancomycin. The swab that would have named the right drug for those 14 patients is not part of that comparison.

Frequently Asked Questions

What Is a Surgical Site Infection?

CDC surveillance treats a surgical site infection as an infection related to an operation that occurs at or near the incision within 30 days, or within 90 days if prosthetic material was implanted. Events are grouped by depth as superficial incisional, deep incisional, or organ-space, and the clock starts on the procedure date rather than on the calendar day of hospital admission.

Why Do Spine Teams Still Give Cefazolin?

ASHP therapeutic guidelines grade cefazolin as the recommended agent for spinal procedures with and without hardware (evidence A) because it covers common skin staphylococci and some gram-negative rods and reaches useful levels in tissue and disc. The same guidelines say second- and third-generation cephalosporins offer no major advantage and should not be used as a broader default.

How Does Medicare Penalize Hospital-Acquired Infections?

The Hospital-Acquired Condition Reduction Program builds a Total HAC Score from six measures: the CMS PSI 90 patient-safety composite plus NHSN ratios for CLABSI, CAUTI, colon and abdominal hysterectomy surgical site infection, MRSA bacteremia, and C. difficile. Every hospital in the worst quartile receives the same 1 percent reduction on all Medicare fee-for-service discharges for the payment year, not a fine limited to the infected cases.

Did Bacteria Spread From Patient to Patient in the Study?

Genomic analysis found no between-patient pathogen transfer and no common-source infection among 1,610 people. NHSN still attributes a qualifying wound infection to the operation for 30 or 90 days after the incision, so an endogenous strain can meet the reporting definition of a healthcare-associated surgical site infection even when it was on the patient before admission.

Do These Findings Apply to Other Types of Surgery?

The authors used instrumented spine surgery because it is a clean incision with little cross-contamination from bowel or trauma, and because it is done across ages and in similar numbers of men and women. The 86% match sits close to older genetic estimates that looked only at Staphylococcus aureus; the paper does not claim a census of abdominal, dirty, or emergency cases.

Disclaimer: This article is news reporting and analysis of published research and public quality-measure rules. It is informational only and is not medical advice, a treatment plan, or a recommendation to change antibiotics, delay surgery, or refuse a procedure. Readers who are preparing for an operation, managing a wound, or deciding about preventive antibiotics should consult a licensed surgeon, infectious-disease physician, or other qualified clinician who knows their history. Figures, protocols, and payment rules reflect the papers and agency documents cited here and may change as new trials, guidelines, or Medicare program years take effect.