ConditionInfections
Surgical Site Infection (SSI)
A surgical site infection (SSI) is an infection that develops at or near a surgical incision within 30 days of an operation, or within 90 days when an implant such as a joint replacement is placed. Signs include increasing redness, warmth, swelling and pain around the wound, pus or cloudy drainage, a wound that opens, and fever. SSIs affect roughly 2 to 5% of patients having inpatient surgery and are mostly caused by skin bacteria such as Staphylococcus aureus. Most are treated successfully with wound care and antibiotics.
Also called: SSI, post-surgical wound infection, postoperative infection, incisional infection, wound infection after surgery
At a glance
- What it is
- Infection of the incision or deeper tissues after surgery.
- Timing
- Usually within 30 days; up to 90 days after implant surgery; most appear 5 to 10 days after surgery.
- Types
- Superficial incisional, deep incisional, and organ or space infections.
- Common bacteria
- Staphylococcus aureus (including MRSA), streptococci, gut bacteria after bowel surgery.
- Risk factors
- Diabetes, obesity, smoking, long or emergency surgery, contaminated procedures, weak immunity.
- Treatment
- Opening and draining the wound, antibiotics, and sometimes further surgery.
When to get help
Call 911 or go to the ER
- Fever with confusion, very fast breathing, a racing heart, low blood pressure or mottled skin after surgery (possible sepsis): call 911 or your local emergency number
- Rapidly spreading redness, severe pain out of proportion, dark or blistering skin around the wound
- A wound that opens widely to show deeper tissue or organs
See a doctor within a day or two
- Increasing redness, warmth, swelling or pain around the incision after the first few days
- Pus, cloudy or foul-smelling drainage from the wound or drain site
- Fever above 38 °C (100.4 °F) in the weeks after surgery
- New or worsening pain deep in the surgical area, or around an implant, even months later
Book a routine appointment
- Mild redness only at the stitch holes, or small amounts of clear or pink fluid in the first days
- Slow healing in people with diabetes or who smoke: keep follow-up appointments
Usually safe to manage at home
- A clean, dry incision with mild tenderness and a thin pink line along the edges in the first week
Types of surgical site infection
The CDC classifies SSIs by depth:
| Type | Tissues involved | Typical signs |
|---|---|---|
| Superficial incisional | Skin and tissue just under the skin | Redness, warmth, swelling, pus from the incision |
| Deep incisional | Muscle and fascia | Deeper pain, wound opening, fever, abscess |
| Organ or space | Any area opened or handled during surgery, such as the abdomen, joint or chest | Abscess, peritonitis, infected implant, fever, organ-specific pain |
What causes SSIs
Most SSIs come from bacteria on the patient's own skin or body entering the wound during or soon after surgery. Common organisms:
- Staphylococcus aureus, including MRSA
- coagulase-negative staphylococci, especially around implants
- streptococci
- gut bacteria (E. coli, Enterococcus, anaerobes) after bowel surgery
Pathology
Bacteria contaminate the wound, multiply and trigger inflammation. Infection overwhelms local defenses when bacterial numbers are high, tissues are poorly supplied with blood or oxygen, foreign material such as sutures or implants provides a surface for biofilm, or the immune response is impaired. An abscess may form, and infection can spread to deeper tissues or the bloodstream.
Risk factors
Patient factors
- diabetes and high blood sugar around the time of surgery
- obesity
- smoking
- older age
- poor nutrition
- weakened immunity, steroids, chemotherapy
- existing infections elsewhere
- MRSA carriage in the nose
Surgical factors
- contaminated or dirty operations, such as bowel surgery or a ruptured appendix
- long operations
- emergency surgery
- implants and foreign material
- blood loss, low body temperature and low oxygen during surgery
- poor timing of preventive antibiotics
Symptoms
- increasing redness spreading from the incision
- warmth, swelling and hardening around the wound
- increasing pain instead of gradual improvement
- pus or cloudy, foul-smelling drainage (wound drainage)
- the wound edges separating (wound dehiscence)
- fever and chills
- feeling generally unwell
Deep and organ infections may show few skin signs and present as fever, pain or delayed recovery.
Diagnosis
- examination of the wound
- wound swab or tissue culture to identify bacteria and guide antibiotics
- blood tests: white cell count, CRP, and blood cultures if fever is high
- imaging: ultrasound or CT to look for abscesses; MRI or specific tests for bone and implant infections
- joint aspiration for suspected infected joint replacements
Treatment
- Opening and draining the infected part of the wound is often the most important step for superficial infections; packing or negative pressure wound therapy helps it heal from the inside.
- Antibiotics: for spreading cellulitis, deep infections or systemic signs; chosen according to culture results.
- Image-guided drainage of deeper abscesses.
- Return to surgery for deep or organ infections, washout, and sometimes removal or exchange of implants.
- Supportive care: blood sugar control, nutrition, and stopping smoking.
Complications
- sepsis
- wound breakdown and hernia
- bone infection (osteomyelitis)
- infected implants needing removal
- longer hospital stay and readmission
Prevention
Before surgery
- stop smoking, ideally 4 or more weeks beforehand
- control blood sugar
- shower or bathe with soap or antiseptic as instructed
- do not shave the surgical area yourself; clippers are used if needed
- treat any existing infections; MRSA screening and decolonization for some surgeries
During and after surgery
Hospitals use antibiotic prophylaxis timed within 60 minutes before incision, skin antisepsis, sterile technique, warming, and glucose control. At home:
- wash hands before touching the wound
- keep dressings clean and dry, and follow instructions for showering
- do not apply creams unless advised
- report warning signs early
Frequently asked questions
What are the signs of infection after surgery?
Signs include redness that spreads, warmth, swelling and increasing pain around the incision, pus or cloudy drainage, a bad smell, the wound opening, fever and chills. Contact your surgical team promptly if you notice these.
When do surgical site infections usually appear?
Most appear 5 to 10 days after surgery, but they can develop up to 30 days later, or up to 90 days after surgery involving implants such as joint replacements or heart devices.
What causes surgical site infections?
They are usually caused by bacteria from your own skin or body, such as Staphylococcus aureus, entering the wound during or after surgery. Risk increases with diabetes, obesity, smoking, long or emergency operations and contaminated procedures.
How is a surgical site infection treated?
Superficial infections are often treated by opening and draining the wound and dressing it, with antibiotics if the infection is spreading. Deeper infections may need drainage of abscesses, further surgery and longer antibiotic courses.
Sources
This guide was written from current patient and clinical guidance, including:
- CDC: Surgical site infection event (National Healthcare Safety Network definitions)
- CDC: Guideline for the prevention of surgical site infection
- World Health Organization: Global guidelines for the prevention of surgical site infection
- American College of Surgeons and Surgical Infection Society: Surgical site infection guidelines
- MedlinePlus: Surgical wound infection, treatment