The NHSN SSI FAQ is a set of official guidance documents published by the Centers for Disease Control and Prevention (CDC) that explains how hospitals should identify, report, and monitor surgical site infections (SSIs) through the National Healthcare Safety Network (NHSN). It provides consistent definitions, coding rules, and data submission procedures to ensure accurate tracking of SSIs across U.S. healthcare facilities.
NHSN SSI surveillance relies on standardized case definitions developed by the CDC's Healthcare-Associated Infections (HAI) Prevention Program. These definitions distinguish between superficial, deep incisional, and organ/space SSIs based on timing, signs, symptoms, and diagnostic testing. The FAQ addresses common ambiguities in applying these definitions, such as whether a wound culture positive for coagulase-negative staphylococcus counts as an SSI or how to handle infections that develop after discharge.
Hospitals use NHSN SSI data to assess surgical outcomes, compare performance across units, and implement targeted prevention strategies. The system supports public reporting, accreditation requirements, and federal quality improvement initiatives like the Hospital-Acquired Condition Reduction Program (HACRP). Without the NHSN SSI FAQ, inconsistent application of criteria could distort national infection rates and undermine patient safety efforts.
NHSN SSI surveillance begins with the collection of patient data during surgery and postoperative follow-up. The system tracks all surgical procedures performed in a facility and monitors patients for signs of infection within a defined window-typically 30 days for most procedures, or up to 1 year for implants.
For each procedure, staff enter details including the type of surgery (e.g., colon resection, hip replacement), the surgical site, and the patient's demographic and clinical data. After surgery, clinicians document any postoperative signs of infection-fever, pain, redness, drainage, or laboratory results indicating infection. If these signs appear within the surveillance period, the case is reviewed against the SSI case definition.
If a case meets the criteria, it is coded as an SSI and reported to NHSN. The system automatically flags potential inconsistencies, such as an infection occurring too early to be classified as a surgical site infection. The FAQ provides detailed examples of these edge cases, such as when a patient develops pneumonia after abdominal surgery-this is not an SSI unless there is direct evidence of wound involvement.
SSIs are categorized into three types based on anatomical location and timing. The NHSN SSI FAQ specifies the exact thresholds for each category, which are critical for accurate reporting.
| Type | Onset Window | Clinical Criteria | Diagnostic Evidence |
|---|---|---|---|
| Superficial Incisional | Within 30 days | Pus, erythema, or tenderness at the incision site | Positive wound culture or imaging showing fluid collection |
| Deep Incisional | Within 30 days | Drainage from deep incision or abscess involving fascia/muscle | Imaging shows deep abscess or surgical drainage required |
| Organ/Space | Within 30 days (or 1 year for implants) | Signs of infection in organs or spaces not closed at surgery | Positive culture from fluid aspirated from the surgical site |
For example, a patient undergoing a laparotomy for appendicitis develops fever and abdominal pain on post-op day 5. A CT scan reveals a fluid collection near the incision site, and a drain yields purulent fluid with gram-positive cocci. This meets the criteria for a deep incisional SSI and must be reported in NHSN.
A common mistake is counting all postoperative fevers as SSIs. The FAQ clarifies that fever alone-without localizing signs or microbiological confirmation-is insufficient. A patient with a temperature of 38.5°C on day 4 after a cholecystectomy who has no wound changes or lab abnormalities does not meet SSI criteria.
One widespread error is assuming that any positive culture from a surgical site constitutes an SSI. The NHSN SSI FAQ explicitly states that contamination must be ruled out. A swab taken from a clean wound during routine dressing change may grow coagulase-negative staphylococci, but this is typically considered colonization, not infection.
Another frequent confusion arises with infections that develop after hospital discharge. The FAQ confirms that infections diagnosed within 30 days of discharge are still reportable if they meet the case definition. For instance, a patient discharged after a total knee arthroplasty returns on day 28 with redness and swelling around the incision. An MRI shows a fluid collection, and blood cultures are positive. This qualifies as an organ/space SSI and must be reported.
There is also a misconception that all SSIs require antibiotic treatment. The FAQ notes that treatment is not part of the definition. A patient may have a confirmed SSI but receive no antibiotics due to allergy or contraindication. The case is still reportable if the clinical and diagnostic criteria are met.
In 2021, a large teaching hospital in New York City used the NHSN SSI FAQ to revise its infection surveillance process. Prior to adopting the FAQ, the facility had inconsistently reported SSIs-some teams classified all wound drainage as SSIs, while others required surgical intervention. After training staff using the FAQ, the hospital reduced false-positive reports by 41% and improved accuracy in identifying true SSIs.
One nurse in the operating room reported that she had previously assumed any wound dehiscence was an SSI. After reviewing the FAQ, she learned that dehiscence without purulent drainage or positive cultures is not an SSI unless it leads to infection. She applied this rule during a follow-up visit and correctly flagged a case of deep incisional SSI only when the patient developed fever and required drainage.
The CDC's NHSN program requires all participating hospitals to complete annual training on SSI case definitions. The FAQ serves as the primary reference for this training. Facilities that fail to align their reporting with the FAQ risk inaccurate benchmarking and may face penalties under federal quality programs.
Accurate SSI reporting enables meaningful comparisons across hospitals and regions. The CDC uses NHSN data to publish national benchmarks and identify high-risk procedures. For example, in 2022, the average SSI rate for colorectal surgeries was 2.1%, but hospitals with rates above 4.0% were flagged for targeted interventions.
Without standardization, differences in reporting practices would obscure real variation in surgical outcomes. A hospital that reports all post-op fevers as SSIs would appear to have a higher infection rate than one that applies the criteria strictly-even if both perform similar surgeries. The NHSN SSI FAQ prevents this distortion.
According to the CDC, adherence to NHSN SSI definitions reduces reporting errors by up to 60%. The agency emphasizes that proper use of the FAQ is essential for valid surveillance and effective infection control. Hospitals that ignore the guidance risk misallocating resources and failing to address actual problems.
The NHSN SSI FAQ is not a static document. The CDC updates it annually based on new evidence and feedback from healthcare providers. The 2023 version included revised criteria for orthopedic implant-related infections, reflecting emerging research on biofilm formation and delayed-onset infections.
Healthcare professionals must consult the current version of the NHSN SSI FAQ before submitting data. Using outdated guidelines leads to invalid reports and undermines institutional credibility. The CDC maintains the latest version at https://www.cdc.gov/nhsn.