A post-surgical infection, known as a surgical site infection (SSI), happens in roughly 2% to 4% of all inpatient surgical procedures, making it the most common preventable complication after surgery. Symptoms typically appear three to seven days after the operation, though infections can develop up to 30 days later, or even 90 days later for certain procedures involving implants. What happens next depends on how deep the infection goes and how quickly it’s caught.
What It Looks and Feels Like
The earliest signs of a surgical site infection tend to show up at the incision itself. You may notice redness or discoloration spreading beyond the edges of the wound, swelling, and warmth when you touch the area around the incision. Pain that was improving may suddenly get worse or change character. Thick, cloudy, white or cream-colored discharge from the wound is one of the most telling signs.
Fever is another common symptom, particularly when the infection has moved beyond the skin’s surface into deeper tissue. Some people also feel generally unwell in a way that’s hard to pin down: fatigue that seems disproportionate to their recovery stage, chills, or a racing heart. These systemic symptoms suggest the infection is no longer purely local.
Three Levels of Severity
Not all surgical infections are equal. They fall into three categories based on depth, and each one carries different implications for your recovery.
Superficial infections involve only the skin and the tissue just beneath it. These are the most common and the least dangerous. You’ll typically see pus, redness, or swelling right at the incision line. Most superficial infections respond well to antibiotics and local wound care without requiring another trip to the operating room.
Deep infections reach into the muscle and connective tissue layers beneath the skin. These are more serious. Signs include pus draining from deeper within the wound, worsening pain, and fever above 38°C (100.4°F). A deep infection sometimes causes the wound to partially reopen on its own. Treatment usually involves opening the wound to let it drain, cleaning out infected tissue, and a longer course of antibiotics.
Organ or space infections are the most severe. These develop in a body cavity or around an organ that was involved in the surgery. For example, an abdominal surgery might lead to an infection in the peritoneal cavity. Pus may drain through a surgical drain if one was placed. These infections almost always require additional surgery and intravenous antibiotics.
How Infections Are Diagnosed
Your surgical team will start with a physical exam of the wound, looking for the classic signs: redness, warmth, swelling, and discharge. If they suspect infection, they’ll typically take a sample of any fluid draining from the wound and send it to a lab to identify the specific bacteria involved. This matters because it tells them which antibiotic will actually work.
Blood tests play a supporting role. Doctors look at your white blood cell count and inflammatory markers. One study on spinal surgery patients found that a specific inflammation marker (CRP) measured on the seventh day after surgery was highly accurate at detecting early infections, with 100% sensitivity at elevated levels. Imaging tests like CT scans or ultrasounds may be ordered if the infection is suspected to be deeper than what’s visible on the surface.
How Post-Surgical Infections Are Treated
Treatment scales with severity. For mild to moderate infections confined to the superficial layers, oral antibiotics are the standard approach. Your doctor will choose an antibiotic based on the most likely bacteria and local resistance patterns, meaning what’s known about which bugs in your area respond to which drugs.
If the infection is more serious or you’re showing signs of being systemically unwell (fever, rapid heart rate, general deterioration), intravenous antibiotics become necessary. This usually means a hospital stay or, in some cases, outpatient IV therapy.
Beyond antibiotics, infected wounds often need physical intervention. Stitches or staples may be removed to let the wound drain. The surgical team will clean out any dead or infected tissue, a process that helps the remaining healthy tissue heal. The wound may then be left open to heal gradually from the inside out rather than being closed again right away. This is called healing by secondary intention, and while it takes longer, it reduces the chance of trapping bacteria inside.
When Infection Requires a Second Surgery
Some infections can’t be resolved with antibiotics and wound care alone. Deep infections and organ or space infections may require a return to the operating room to wash out the infected area and remove damaged tissue.
Joint replacement infections present a particularly challenging scenario. When a prosthetic hip or knee becomes infected, the implant itself can harbor bacteria in a way that antibiotics alone can’t reach. The standard treatment is a two-stage revision: the infected implant is removed, the infection is treated over a period of weeks to months, and then a new implant is placed. In one study of 78 patients with chronic knee replacement infections treated this way, 82% were successfully reimplanted after an average interim period of about 90 days. That’s three months between surgeries, during which patients have limited mobility.
The Risk of Sepsis
The most dangerous outcome of a post-surgical infection is sepsis, which occurs when the infection triggers a cascading immune response throughout the entire body. Skin infections, including surgical wounds, are one of the common starting points. In sepsis, your body’s attempt to fight the infection starts damaging its own tissues and organs.
Signs that an infection may be progressing toward sepsis include high fever or abnormally low temperature, confusion or disorientation, rapid breathing, a heart rate that stays elevated, and skin that looks mottled or discolored beyond the wound area. Without fast treatment, sepsis can lead to organ failure and death. This is why seemingly minor wound infections warrant attention early, before they have a chance to spread into the bloodstream.
Factors That Raise Your Risk
Certain people are more likely to develop a surgical site infection than others. Diabetes is one of the most significant risk factors, particularly when blood sugar is poorly controlled before and after surgery. Smoking impairs blood flow to healing tissues and weakens the immune response at the wound site. Obesity increases risk because fatty tissue has a lower blood supply, making it harder for immune cells and antibiotics to reach the surgical site.
The type and length of surgery matter too. Longer operations expose tissue to the environment for more time. Emergency surgeries carry higher infection rates than planned procedures, partly because there’s less opportunity for preventive measures like pre-surgical skin preparation and properly timed antibiotics. Surgeries involving the gastrointestinal tract also carry elevated risk because of the bacteria naturally present in the gut.
If you’re planning a surgery, the factors you can influence beforehand include quitting smoking (even a few weeks before surgery helps), optimizing blood sugar control if you have diabetes, and following your surgical team’s instructions about pre-operative skin cleansing. After surgery, keeping the wound clean and dry, washing your hands before touching the area, and watching for early warning signs all reduce the chance of a minor issue becoming a serious one.