A surgical site infection (SSI) occurs when pathogens multiply at the site of a surgical incision, resulting in an infection. Urinary tract infections and respiratory infections can happen after any surgery, but SSIs are only possible after surgery that requires an incision.

SSIs are fairly common, occurring in 2 to 5 percent of surgeries involving incisions. Rates of infection differ according to the type of surgery. As many as 500,000 SSIs happen in the United States annually. Most SSIs are staph infections.

There are three types of SSIs. They’re classified according to how serious the infection is. Infections are caused by germs that enter your body during or after surgery. In severe cases, SSIs can cause complications, including sepsis, an infection in your blood that can result in organ failure.

An SSI is classified as an infection that begins at the site of a surgical wound fewer than 30 days after the incision is made. Symptoms of an SSI after surgery include:

  • redness and swelling at the incision site
  • drainage of yellow or cloudy pus from the incision site
  • fever

An SSI that only affects the layers of your skin where your stitches are is called a superficial infection.

Bacteria from your skin, the operating room, a surgeon’s hands, and other surfaces at the hospital can be transferred into your wound around the time of your surgical procedure. Since your immune system is focused on recovering from surgery, the germs then multiply at the site of your infection.

These types of infections can be painful but usually respond well to antibiotics. Sometimes your doctor may need to open part of your incision and drain it.

A muscle and tissue wound infection after surgery, also called a deep incisional SSI, involves the soft tissues surrounding your incision. This kind of infection goes deeper than your skin layers and can result from an untreated superficial infection.

These can also be the result of medical devices implanted in your skin. Deep infections require treatment with antibiotics. Your doctor may also have to open your incision completely and drain it to get rid of infected fluid.

An organ and space infection after a surgery involves any organ that’s been touched or manipulated as a result of a surgical procedure.

These kinds of infections can develop after an untreated superficial infection or as the result of bacteria being introduced deep in your body during a surgical procedure. These infections require antibiotics, drainage, and sometimes a second surgery to repair an organ or address the infection.

Infections in older adults. Health conditions that compromise your immune system and can increase your risk for an infection include:

If you think you have an SSI, you should contact your doctor right away. Symptoms include:

  • soreness, pain, and irritation at the site
  • a fever that spikes at about 100.3°F (38°C) or higher for more than 24 hours
  • drainage from the site that’s cloudy, yellow, tinged with blood, or foul or sweet smelling

The Centers for Disease Control and Prevention provides regularly updated for doctors and hospitals to help prevent SSIs. You can also take actions before and after surgery to make an infection less likely to develop.

Before surgery:

  • Wash with an antiseptic cleanser from your doctor before you head to the hospital.
  • Don’t shave, as shaving irritates your skin and can introduce infection under your skin.
  • Quit smoking before you have surgery, as smokers develop . Quitting can be very difficult, but it’s possible. Speak to a doctor, who can help you develop a quit smoking plan that’s right for you.

After your surgery:

  • Maintain the sterile dressing that your surgeon applies to your wound for at least 48 hours.
  • Take preventive antibiotics, if prescribed.
  • Make sure you understand how to take care of your wound, asking questions if you need clarification.
  • Always wash your hands with soap and water before touching your wound and ask anyone who may assist in your care to do the same.
  • Be proactive in the hospital about your care, paying attention to how often your wound is being dressed, if your room is sterilized and clean, and if your caretakers are washing their hands and wearing gloves when handling your incision.

SSIs aren’t uncommon. But doctors and hospitals are working all the time to bring down the rates of SSIs. In fact, SSI rates related to 10 major procedures decreased by between 2015 and 2016.

Being aware of your risk prior to surgery is the best way to avoid infection. Your doctor should follow-up to check your incision for signs of infection after most surgeries.

If you’re concerned that you might have an SSI, call the doctor right away. The main complications of SSIs come from waiting too long to get treatment.