SSIs (also called surgical wound infections, SWIs) are the second or third most common type of healthcare-acquired infections and affect surgery worldwide, with considerable social, professional, legal, and economic impact (Mangram et al. 1999). SSIs were listed as the second most common adverse event among hospitalized patients in a 1984 study in hospitals in New York State (Brennan et al. 1991; Leape et al. 1991). The US Centers for Disease Control (CDC) Guidelines for Prevention of Surgical Site Infection1 reported an overall rate of 2.6 % SSIs among approximately 600,000 operations in US hospitals from an analysis within a study period between 1986 and 1996. It has been estimated that on average, each SSI increases the stay in hospital by about 7–10 days and results in about US$2,000 to 3,000 of extra costs (Mangram et al. 1999). Given an annual number of about 30 million operations in the US, this results in more than 700,000 SSIs annually and more than US$2 billion of extra healthcare costs. In Australia, the overall infection rate was estimated at 4.6 % in a national study published in 1988 (McLaws et al. 1988) and ranges between about 1.2 and 7.5 %, depending on the type of operation, in the reports of the Victorian Nosocomial Infection Surveillance System (http://​www.​vicniss.​org.​au). According to the Australian Institute of Health and Welfare, the estimated annual excess healthcare cost in Australia from SSIs is about A$268 million (Australian Council for Safety and Quality in Health Care 2004). European data have been found to vary widely, with SSI rates reported between 1.5 and 20 % and the annual economic burden in the range of Eur 1.47 to 19.1 billion (Leaper et al. 2004).

The causation of SSIs is complex and multifactorial, with many contributing and preventing factors involved (Mangram et al. 1999). Thus, it becomes very difficult, often impossible, to determine the “cause” in a given case of SSI. In a general sense, the risk of SSI is determined by the “dose” of microbial contamination to the surgical site, the virulence of the pathogen, and the resistance (or lack thereof) of the patient (Mangram et al. 1999). The latter includes underlying illnesses, immunological disturbances, and the type and site of surgery. Various risk factors for SSIs can be broadly divided into host factors, preoperative factors, surgical factors, and environmental factors (Table 3.1).

A reflection of host factors associated with SSI risk is the general preoperative physical status of a patient; this is addressed in the physical status classification of the American Society of Anesthesiologists, also called ASA score (Mangram et al. 1999). This classification divides the preoperative status of a patient into five simple, intuitive categories from normal and healthy to moribund (Table 3.2).

Most SSIs are caused by microorganisms from patients’ skin, mucous membranes, and intestinal organs (Mangram et al. 1999). The role of skin microorganisms in SSI pathogenesis has been documented since the early 1900s, thus explaining the role of and providing a strong microbiological and theoretical rationale for preoperative skin antisepsis (“skin prep”) (Gröschel and Pruett 1991). Indeed, in “clean” surgery, where no mucous membranes or viscera are involved, skin flora causes most SSIs. However, in surgery through mucous membranes, intestinal surgery, or contaminated or infected surgery, the relative role of skin-based organisms decreases and that of the other sources increases, which underscores the multifactorial nature of SSIs (Gröschel and Pruett 1991; Wong 2004).

Dependent on the burden of microorganisms encountered during an operation, surgical wounds can be classified into four broad categories, ranging from clean to dirty infected (Table 3.3). These four categories are strongly linked with SSI risk and are commonly used to stratify and compare SSI rates in SSI surveillance projects (Mangram et al. 1999). Interestingly, the greatest relative improvements in lowering SSI rates in the last 20–30 years have been made in contaminated and dirty-infected surgery; the rates in clean and clean-contaminated surgery have remained relatively stable (Mangram et al. 1999). This is likely reflecting the fact that aseptic techniques have already been introduced (and must have been effective) in the first half of the twentieth century, while routine antimicrobial prophylaxis was introduced in the 1970s.

The relative risk of development of an infection after surgery is associated with the type of wound, degree of bacterial contamination, and the time since surgery/injury. Wounds have been classified into four main classes, which is a widely used system for monitoring and communication of results between institutions. These categories are: Clean, Clean-contaminated, Contaminated and Dirty (Table 3.3).

Many different bacterial and fungal pathogens can cause SSIs, but there is a range of common pathogens. For example, S. aureus (including methicillin-resistant S. aureus, MRSA), coagulase-negative staphylococci, Enterococcus spp., Escherichia coli, Pseudomonas aeruginosa, and Enterobacter spp. are common (Mangram et al. 1999). Also, the spectrum of pathogens varies with body site, type of operation, and surgical discipline. For example, in cardiac, orthopedic, vascular, and neurosurgery, S. aureus and coagulase-negative staphylococci are more common. In gastrointestinal surgery, Gram-negative (“enteric”) bacteria and anaerobes predominate. In obstetric and gynecologic surgery, Gram-negatives, anaerobes, group B streptococci (Streptococcus agalactiae), and enterococci are more common.

According to the CDC guidelines (Mangram et al. 1999), there are three types of SSIs, depending on anatomical location:

Superficial incisional SSIs involve skin and subcutaneous tissue; deep incisional ones involve deep soft tissue, such as fascia and muscle; and organ/space SSIs mostly involve deep-seated organs that were targets of the operation, such as the intestines, liver, and heart. Organ/space SSIs account for approximately one-third of the total number of SSIs, and by their nature, they are the most severe type, often with serious life-threatening consequences.

SSIs can be diagnosed by a combination of clinical and microbiological findings. In general, the diagnosis of an SSI can be based on the following:

The CDC guidelines (Mangram et al. 1999) further specify a 30-day follow-up period after most common types of surgery, and a 1-year period if a surgical implant has been left in place, such as an artificial joint, prosthetic heart valve, or nonhuman vascular graft. This has important implications, because (1) SSIs may be overlooked or underdiagnosed if patients are not followed up for the appropriate period, (2) SSIs continue to cause healthcare costs after hospital discharge (Graves et al. 2006) (and even after 30 days), and (3) this requires additional logistic and personnel resources for the implementation of SSI surveillance programs.

Deep organ/space infections are often more difficult to diagnose than suggested by the above criteria. They may require radiologic examination (e.g., ultrasound, computed tomography, magnetic resonance imaging), imaging-guided needle aspiration, biopsy with histopathology, or reoperation to be diagnosed. Regardless of SSI type, it is important to note that tissue, fluid or pus samples are always preferable to swabs when samples are obtained for microbiological examination during invasive procedures, such as invasive biopsies or reoperation. Such samples have greater diagnostic yield in the microbiology laboratory than swabs, and samples are often difficult to re-obtain invasively when pathogen isolation fails.

Consistent with the multifactorial nature of SSIs, there are many different measures to implement and observe in order to minimize the occurrence of SSIs. Many of these measures have developed historically, since the original implementation of antisepsis in surgery by Lister in the 1860s and then the introduction of aseptic surgery in the early 1900s (Gröschel and Pruett 1991). Thus, the contemporary practices in surgery are based on a large, complex framework of historical developments, empirical observations, many individual surgeons’ clinical experiences, microbiological and other experimental data, animal experiments, inference from knowledge of how infections are transmitted, and more recently, data from controlled clinical trials. Key measures of good surgical practice in order to prevent infections are listed in Table 3.4, and some of these measures will be explained further.

Measures of antisepsis, disinfection, and sterilization are essential components of modern surgery; they allowed the rapid developments in surgery that began in the early twentieth century (Gröschel and Pruett 1991). Sterilization is essential for the usage of surgical instruments and other supplies needed during operations. Main sterilization techniques are:

Most major hospitals have sterilization departments, and it is important that surgical supplies (e.g., instruments) are cleaned well before re-sterilization and that all sterilization processes are monitored and quality controlled. Surgeons are now rarely confronted with technical questions of sterilization, and failure of sterilization processes is rare at facilities where a good infrastructure is in place, but when failure occurs, it can have severe consequences for patient safety.

There are two major types of antisepsis involved in surgical procedures:

The rationale for surgical hand antisepsis is to significantly reduce the bacterial count on arm and hand skin to reduce the transfer of microorganisms to the patient by (1) unrecognized punctures in surgical gloves during the operation (up to ~35 %), (2) tiny holes present in a small percentage of new gloves, and perhaps (3) accidental touching of the wound after removal of gloves (World Health Organization 2009). This rationale is further supported by published clusters of SSI cases following breaches of hand antisepsis protocols (World Health Organization 2009; Grinbaum et al. 1995). The protocols and substances vary; for example, continental European countries have traditionally preferred alcohol solutions, while aqueous detergent-based antisepsis with chlorhexidine or povidone-iodine has been preferred in the USA, UK, and Australasia. Time of surgical hand antisepsis is another parameter; typically, 3–5 min (up to 10) are recommended. Commonly, alcohol-based protocols lead to a reduction of transient and resident microorganisms by about 2–3 logs (~100–1,000-fold), while detergent-based methods reach about 1- to 2-log reductions (Gröschel and Pruett 1991). While no differences in SSI rates have been detected so far, other advantages of alcohols are better skin tolerability of commercial products with added emollients (i.e., skin moisturizers) and shorter overall scrubbing times. There is some evidence that after the initial scrub for the day, subsequent scrubs can be reduced to 1 min with equivalently effective antisepsis, especially for chlorhexidine-based wash solutions (Watts et al. 1981).