Importance of infection

In the latter half of the 19th century Louis Pasteur hypothesized that bacteria caused infection by being carried through the air (germ theory of disease). Aware of Pasteur’s work, in 1865, Joseph Lister first used carbolic acid (phenol) as a spray in the operating theatre to successfully prevent and treat infection in compound fractures. In the early part of the 20th century, with the advent of sterilized instruments, surgical gowns and the first rubber gloves, antisepsis was replaced by modern aseptic surgical techniques which were championed by Birmingham surgeon Robert Lawson Tait. Penicillin was discovered by Alexander Fleming in 1928 and first used clinically in 1940 by Howard Florey. The prevention and treatment of surgical infection was further transformed by the many different classes of antibiotics that were discovered through the latter part of the 20th century. Nevertheless, control of infection in surgical practice remains an important and challenging issue due to the emergence of antibiotic-resistant organisms and the rise in the numbers of elderly, co-morbid and immunocompromised patients undergoing increasingly complex surgical interventions that frequently involve the use of implants. The risk of infection is related to the type of surgery (Table 4.1). Postoperative infections impact on patient outcomes and increase the length of hospital stay, which in turn increases the cost of surgery. In the UK, there is now a legal duty on hospitals to do all they can to minimize the risk of healthcare associated infections (HCAI) in patients.

Table 4.1 Classification of operative wounds and infection risk with prophylaxis

* Based on data from: Olson M, O’Connor M, Schwartz ML. Surgical wound infections. A 5-year prospective study of 20,193 wounds at the Minneapolis VA Medical Center. Ann Surg. 1984 Mar;199(3):253–259.

Biology of infection

Many body surfaces are colonized by a wide range of micro-organisms, called commensals, with no ill effects (Fig. 4.1). However, once the normal defences are breached in the course of surgery, such as skin (e.g. Staphylococcus aureus) and bowel (e.g. Bacteroides spp. and Escherichia coli) commensals can then cause infection. Infection is defined as the proliferation of micro-organisms in body tissue with adverse physiological consequences. The factors involved in the evolution of infection are shown in Figure 4.2.

Fig. 4.1 Distribution of normal adult flora.

Mucosal or skin breaches may allow normal flora to infect usually sterile sites. Overgrowth by potentially pathogenic members of the normal flora may occur with changes in normal composition, e.g. after antimicrobial treatment, local changes in pH (vagina and stomach) or defective immunity (e.g. AIDS or immunosuppressive treatment). The most common yeast is Candida albicans. *Staphylococcus epidermidis is the most common ’coagulase-negative staphylococcus’ frequently found on skin. Density of colonization varies greatly with age and site.

Fig. 4.2 Factors important in the development of infection and their inter-relationship.

Preventing infection in surgical patients

All UK hospitals now have infection prevention programmes which include measures to minimize risks to patients and staff from infections which may be acquired during and after surgery.

Preoperative MRSA screening

Since 2008 hospitals in England have been required to screen all elective surgical patients for methicillin-resistant Staphylococcus aureus (MRSA). Carriers receive decolonization treatment (nasal mupirocin cream and antiseptic skin wash) and appropriate antibiotic prophylaxis, usually a glycopeptide antibiotic (e.g. teicoplanin) prior to surgery. This policy reduces MRSA transmission in surgical wards (EBM 4.1). Screening for nasal carriage of Staphylococcus aureus followed by decolonization also reduces surgical wound infection (EBM 4.2). These hospitals now screen emergency admissions although the timing of available results will determine whether this has an impact on management and outcomes.

4.1 Preventing MRSA transmission in surgical patients by rapid polymerase chain reaction (PCR) screening for MRSA

‘A prospective, cluster, two-period cross-over design trial where all MRSA positive patients were decolonized and isolated (only for 17% patients). Infection control practices were the same in both groups.

13 952 patient wound episodes included and results showed that patients on wards using conventional screening were 1.49 times (p = 0.007) more likely to acquire MRSA. It was concluded that rapid PCR screening and decolonization reduces transmission of MRSA.’

Hardy K, et al. Reduction in the rate of methicillin-resistant Staphylococcus aureus acquisition in surgical wards by rapid screening for colonization: a prospective, cross-over study. Clin Microbiol Infect. 2010; 16:333-9.

4.2 Preventing surgical site infections in nasal carriers of Staphylococcus aureus

‘A randomized, double-blind, placebo-controlled, multicentre trial over 20 months where a total of 6671 patients were screened for S. aureus nasal carriage using PCR. The subgroup of surgical-site infections caused by S. aureus was reduced by 60% among those in the active treatment group (nasal mupirocin ointment plus chlorhexidine wash) as compared to those in the placebo group.’

Bode LG, et al. Preventing surgical-site infections in nasal carriers of Staphylococcus aureus. N Engl J Med. 2010; 362:9-17.

Aseptic technique

The term ‘aseptic technique’ refers to specific practices performed immediately before and during a surgical procedure to reduce postoperative infection. These include hand washing, surgical scrub, skin preparation of the patient, maintaining a sterile field and using safe operating practices.

Hand decontamination

The operating team should wash their hands prior to each operation on the list using an aqueous antiseptic surgical solution, with a single-use brush for the nails. The ‘six-step hand hygiene technique’ is now widely adopted (Fig. 4.3). Hospitals will have policies for which antiseptic agents are used. Where hands are not soiled, alcohol hand gel is a suitable alternative for decontamination on the wards.

Fig. 4.3 Six-step hand hygiene technique.

Personal protective equipment (PPE) for staff

The operating team should wear sterile gowns and gloves during the operation. Consideration should be given to wearing two pairs of gloves when there is a high risk of perforation and the consequences of contamination may be serious (e.g. in patients known or suspected to be infected with blood-borne viruses, (BBV)). Visors and goggles can be worn to protect from splash inoculation with body fluids.

Skin preparation

Although it is not possible to sterilize the skin, antiseptics such as chlorhexidine or povidone-iodine applied to the surgical site prior to incision reduce the number of resident organisms and so the risks of wound infection. Antiseptics containing alcohol must be allowed to evaporate completely before using diathermy.

Surgical instruments

To prevent cross-infection only sterile instruments are used. Sterilization is usually undertaken in Sterile Services Departments (SSD) in hospitals.

Terminology

• Decontamination: a process which removes or destroys infectious or unwanted material

• Cleaning: the physical removal of soil and organic matter

• Disinfection: the removal or destruction of some micro-organisms but not bacterial spores

• Sterilization: the complete destruction of all micro-organisms including spores.

Used surgical instruments are first thoroughly washed in automated washer disinfectors which reach temperatures of 85–95°C (thermal disinfection), remove organic matter and kill most micro-organisms except spores. Instruments can then be packed and processed in a steam sterilizer or autoclave to destroy any remaining micro-organisms and their spores. Pressures above atmospheric are used so that higher temperatures can be achieved (e.g. 121°C for 20 minutes; 134°C for 5 minutes).

Creutzfeldt–Jakob disease (CJD) and other prion diseases

These normal decontamination processes do not destroy prions (infectious agents composed only of protein) and so patients known to have, or at risk of, CJD must be identified prior to surgery. Wherever possible, disposable surgical instruments are used. Whether disposable or not, all instruments used on such patients must be subsequently destroyed by incineration.

Summary Box 4.1 Prevention of infection

• Preoperative screening of patients for MRSA, and subsequent decolonization of carriers, is now an integral part of surgical care in UK hospitals

• The routine practices of hand washing, surgical scrub, skin preparation of the patient and maintaining a sterile field are collectively known as ‘aseptic technique’

• The practice of aseptic technique is an important component in preventing surgical site infections

• Sterility of surgical instruments is critical to preventing cross-infection. This may be achieved by decontamination of instruments in SSDs or by using sterile, disposable instruments.

Prophylactic use of antibiotics

Antibiotic prophylaxis is defined as their use before, during, or after a diagnostic, therapeutic, or surgical procedure to prevent infectious complications. The evidence base and guidance can be found at www.sign.ac.uk/pdf/sign104.pdf and in the British National Formulary (BNF).