What is a Surgical Site?

A surgical site is the incision or cut in the skin made by a surgeon to carry out a surgical procedure and the tissue handled or manipulated during the procedure. The position and size of the surgical site depends on the type of operation and the type of surgery. For example, laparoscopic surgery (which uses fine instruments and a video-camera) requires very small incisions whereas more complex surgery may require a very large incision.

What is Surgical Site Infection (SSI)?

A surgical site infection occurs when micro-organisms get into the part of the body that has been operated on and multiply in the tissues. This results in physical symptoms as the body tries to fight the infection. There may be pus, inflammation, swelling, pain and fever.

Most SSI are limited to the incision or cut that the surgeon has made through the skin in order to carry out the operation, but can occasionally spread to deeper tissues. These infections can develop at any time from two to three days after surgery until the wound has healed (usually two to three weeks after the operation). Very occasionally, an infection can occur several months after an operation particularly when an artificial implant has been used, for example a hip replacement.

There are many bacteria (micro-organisms) that live on our skin and in other parts of our body where they do no harm.  Micro-organisms causing these infections are those commonly found on the skin or other parts of the body that harbour lots of germs, such as the gut. Occasionally they can come from the environment. Surgical wound infections are uncommon. However, some types of surgery carry a greater risk of surgical wound infection than others, for example operations on the bowel, because of the large numbers of micro-organisms present in the operation site at the time of the operation. See ‘Wound Classification’ below for more details.

• There are different levels of SSI:
• Superficial incisional, affecting the skin and subcutaneous tissue.
• Deep incisional, affecting the facial and muscle layers.
• Organ or space infection affecting any part of the anatomy opened or manipulated during the operation.

Infections acquired in hospital cause anxiety and discomfort, complicate illness and delay recovery. It has been estimated that the annual cost nationally is almost £1 billion. Infections of the surgical wound are an important cause of morbidity for patients undergoing surgery. The delay in recovery also has economic consequences. It has been estimated that each patient with a surgical site infection requires an additional hospital stay of 6.5 days and hospital costs are doubled (Plowman et al 2001).

Why do surgical site infections occur?

SSI are relatively rare. High standards of asepsis (procedures that reduce the risk of bacterial contamination e.g. sterile equipment) in operating theatres, and appropriate use of antibiotics are key to minimising the risk of infection. However, they can not always be prevented. The likelihood of an SSI depends on a number of factors related to both the patient and the surgical procedure. In particular, the risk of developing a SSI varies according to the type of surgery, (see Wound Classification below) the general health of the patient at time of operation and the length of the operation.

Wound classification

Rates of SSI vary between types of surgery because the risk of micro-organisms entering the wound depends on the parts of the body involved in the procedure. Some areas of the body are normally sterile, whereas other parts may have many bacteria already present. This variation is captured by the standard wound classification system and reflected in the variation in rates of SSI found in different types of surgery.

The following link takes you to a table that shows categories of surgical procedure and national rates of SSI based on aggregated data submitted to the Surgical Site Infection Surveillance Service from October 1997 to December 2005. These rates represent a benchmark against which hospitals can compare their own rates of SSI in specific types of operation.

Information leaflet

Click on this link for an information leaflet for Monitoring surgical wounds for infection. Information for patients (PDF, 1 MB)