Part of the TeachMe Series

Surgical Site Infection

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Original Author(s): Tom Jay Grundy
Last updated: March 18, 2019
Revisions: 28

Original Author(s): Tom Jay Grundy
Last updated: March 18, 2019
Revisions: 28

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surgical site infection (SSI) is an infection that occurs in the wound created by an invasive surgical procedure.

SSI is a leading cause of in hospital morbidity, increasing ITU admission rates by 60%, doubling mortality rates and increasing length of stay.

The primary aim is prevention through meticulous technique and patient optimisation. However, despite the necessary precautions taken, there is always the risk of infection in or around the area that has been instrumented in surgery.

In this article, we shall look at the risk factors, clinical features and management of surgical site infections.

Rates of Surgical Site Infection

The rates of SSI vary depending on the type of surgery. A large widely-referenced cohort study focusing on rates of SSI documents significant variations depending on the degree of contamination:

  • 2.1 for every 1000 operations, for clean surgery
  • 3.3 for every 1000 operations, for clean contaminated surgery
  • 6.4 for every 1000 operations, for contaminated surgery
  • 7.1 for every 1000 operations, for dirty surgery

Risk Factors

There are several factors that increase the risk of a surgical site infection, as shown in Table 1:

Patient Factors Operation Factors
Extremes of age

Poor nutritional state

Diabetes mellitus or renal failure


Co-existing infection at other site


Long post-operative stay

Preoperative shaving

Length of operation

Foreign material in surgical site

Insertion of surgical drain

Inadequate instrument sterilisation

Poor closure of wound

Post-operative hypothermia

Post-operative haematoma or lymphatic leak

Site of procedure (e.g. at a skin crease)

Table 1 – Risk Factors for Surgical Site Infections

Clinical Features

The symptoms of a surgical site infection typically appear 3-7 days post-procedure, however can develop up to 3 weeks after*.

*Infections of a prosthetic insertion can present later, up to several months after the original operation, often due to bacterial spread from another location infecting the wound site

The common clinical features of surgical site infections include:

  • Spreading erythema
  • Localised pain
    • This is often different to the typical post-operative pain
  • Pus/discharge from the wound
  • Wound dehiscence
  • Unexplained persistent pyrexia
Fig 1 - (A) Purulent discharging forming in open wound; (B) Erythema and pus seen in closed wound; (C) drain placed in situ to remove any potentially accumulating pus.

Fig 1 – (A) Purulent discharging forming in open wound; (B) Erythema and pus seen in closed wound; (C) drain placed in situ intra-operatively to remove any accumulating serous fluid

Most surgical site infections are superficial, however some may be deeper and can result in extensive wound breakdown. Fortunately, the need for debridement and open wound care is rare in clinical practice.


Any suspected surgical site infection should have wound swabs taken for culture at the wound site, especially if purulent, avoiding wound edges where possible to reduce skin flora contamination. Perform blood tests for infection markers (FBC, CRP), and take blood cultures if evidence of systemic involvement or sepsis.


The management of a surgical site infection follows four main principles:

  • Removal of sutures/clips – this may seem counterintuitive to open the wound, however this allows for the drainage of pus and the opportunity for the wound to be packed if required
  • Discharge or drainage of any pus
  • Empirical antibiotic prescription – Different wounds are often caused by different organisms (e.g. a laparotomy wound infection is more likely to be caused by an E. Coli organism) however best practice is to follow local hospital empirical antibiotic guidelines, tailoring antibiotic therapy following culture results
  • Monitor closely for signs of systemic infection or sepsis and treat accordingly


The prevention of surgical site infections can be achieved in the pre-operative, intraoperative, and post-operative settings.

Pre-Operative Phase

  • Give prophylactic antibiotics if indicated (clean surgery involving a prosthesis, clean-contaminated surgery, or contaminated surgery)
  • Do not remove hair routinely – if necessary do this immediately prior to surgery with an electric clipper (as the use of razors to remove hair actually increases the risk of SSI)
  • Patient advice – shower prior to surgery, weight loss to avoid sweaty skin folds around incision if required, good nutrition to promote wound healing, good diabetic control, smoking cessation.

Intraoperative Phase

  • Prepare the skin at the surgical site immediately before the incision using an antiseptic preparation (povidone-iodine or chlorhexidine are most suitable)
    • multi-centre study showed that wound edge protectors do not appear to provide any additional benefit
  • Change gloves or gowns if you become contaminated
  • Wear appropriate hair nets and face masks
  • Use an appropriate interactive dressing at the end of the operation to cover all surgical incisions

Post-Operative Phase

  • Monitor wounds closely – the use of see-through dressings* will limit the number of dressing changes, thus minimising the chance for bacterial contamination.
  • Ensure that wounds in difficult areas such as skin creases and underneath skin folds (such as groin) are closely observed. Patients may require pads to separate the wound from overlying skin or be bed bound to remove pressure on a wound.
  • Refer to a tissue viability nurse for advice on appropriate dressings for the management of surgical wounds that are healing by secondary intention.

Topical antibiotics are used in some cases post-operatively as well; a meta-analysis has shown that topical antibiotics probably do prevent SSI rates when compared with no topical antibiotic or antiseptic therapy

*Whilst wounds are dressed as routine post-surgical care, recent work has identified that there is no difference in the rates of surgical-site infection between wounds covered with different dressings and those left uncovered, nor differences noted in pain, scar, or acceptability between dressings

Key Points

  • Surgical site infections are a leading cause of in hospital morbidity, rates dependent on the type of surgery performed
  • Often appearing 3-7 days post-operatively, symptoms include spreading erythema, localised pain, pus/discharge from the wound, or a persistent pyrexia
  • Primary prevention is the optimal way in reducing surgical site infections, with several evidence-based interventions possible
  • Any case of surgical site infection should be regularly monitored, with any clips or sutures removed where feasible, any pus present is suitably drained, and empirical antibiotics prescribed