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).

Management of surgical infections

Surgical infections are of two types; those that occur in patients who:

WCC, white cell count; MAP, mean arterial pressure, SBP systolic blood pressure; INR, international normalized ratio; APTT, activated partial thromboplastin time.

http://www.survivingsepsis.org/

Table 4.3 Severe sepsis care pathway

http://www.survivingsepsis.org/

Antibiotic therapy

Antibiotics are almost inevitably an adjunct to surgical treatment in surgical infections e.g. drainage of abscesses, debridement, excision of infected tissue or lavage of a serous cavity.

Table 4.4 Principles underlying antibiotic policy

Table 4.5 Antibiotics in surgery: suggestions for specific therapy

These suggestions should be considered in the light of local epidemiology, sensitivities, drug availability, site and severity or infection.

* Gould FK et al. Guideline (2008) for the prophylaxis and treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections in the UK. J. Antimicrobial Chemotherapy 2009;63:849-861

Table 4.6 Empirical therapy for acute infections

Note The suggestions are for occasions when immediate treatment is necessary. Amendments may be necessary in the light of local epidemiology.

Specific infections in surgical patients

Urinary tract infections (UTI)

These are common and may range from simple cystitis to pyelonephritis or even perinephric abscess. Catheterized patients are at increased risk of infection. The most common organisms are Escherichia coli, Klebsiella species, Enterococcus faecalis and Pseudomonas aeruginosa. Multi-resistant organisms such as ESBL-producing E. coli and MRSA are increasingly being seen and can be difficult to treat. Symptoms include dysuria, fever and, in patients who are not catheterized, frequency and nocturia. Cystitis may not give rise to any clinical signs. Pyelonephritis is typically associated with rigors, renal angle pain and tenderness. Urine samples must be sent for microscopy and culture. In catheterized patients the urine frequently contains organisms but not white cells. This does not require antibiotics unless there are signs of systemic illness. The urine will not become sterile until the catheter is removed. Trimethoprim, gentamicin and co-amoxiclav are reasonable antibiotic choices until sensitivities become available. Fluoroquinolones (e.g. ciprofloxacin) may be used although C. difficile infection is a risk particularly in elderly patients. Expert advice should be sought in the case of multi-drug resistant pathogens. Aseptic introduction and meticulous care of the urinary catheter helps to prevent bacteria entering the urinary tract (Fig. 4.4).

Fig. 4.4 Routes of entry of uropathogens into the catheterized urinary tract.

Infections primarily treated by surgical management

Abscess

This is a localized collection of pus containing neutrophils, dead tissue and organisms that can develop anywhere in the body. The commonest pathogen is Staphylococcus aureus. Abscesses in the abdomen or pelvis often contain a mixture of gut bacteria e.g. E. coli, enterococci and anaerobic bacteria. Abscesses close to the skin are often painful and the overlying skin will be raised, red and hot to the touch. Large or multiple skin abscesses may cause systemic upset. Deeper abscesses may present with a ‘swinging’ pyrexia, systemic upset and symptoms relating to pressure on surrounding tissues. The pus must be drained and sent for microscopy and culture. This can be achieved through needle aspiration (e.g. breast), radiologically under ultrasound or CT guidance (e.g. subphrenic), or via open surgery (e.g. perianal). Antibiotics do not usually penetrate into abscesses but may be required for treatment if the patient is systemically unwell or for prophylaxis if a surgical wound is being made in the course of drainage.

Necrotizing fasciitis

This is an uncommon but severe, life-threatening infection of skin and subcutaneous tissues characterized by necrosis of deep fascia (Fig. 4.5). There are two main types depending on causative organisms.

• Type I: Polymicrobial aetiology which is also known as synergistic bacterial gangrene; Fournier’s gangrene is a special type affecting the perineal area

• Type II: Single organism infection, usually by β-haemolytic Group A streptococci (Streptococcus pyogenes).

Fig. 4.5 Necrotizing fasciitis of the lower limb.

(Courtesy of the Medical Microbiology Dept., University of Edinburgh.)

The infection usually starts at a site of (often minor) trauma and can spread very quickly as bacterial exotoxins and enzymes lead to necrosis of fat and fascia and eventually overlying skin. The patient is usually febrile, toxic and in severe pain. Initially, the overlying skin may appear deceptively normal but as the infection progresses there is oedema, discoloration and crepitus (due to gas production). Urgent surgical debridement of all necrotic tissue is essential and several visits to theatre may be required. Initial antibiotic choice is usually empirical with a combination of broad-spectrum agents against likely pathogens e.g. carbapenems, clindamycin and metronidazole. Antibiotic therapy can later be tailored according to the results of pus and tissue cultures.

Diabetic foot infections

Infections involving the feet in diabetic patients range from cellulitis to complex skin and soft tissue infection to chronic osteomyelitis. Clinical diagnosis is based on the presence of cellulitis, purulent discharge, pain, tenderness and gangrene. Signs of systemic toxicity may be present in severe infection. Microbiological diagnosis is best achieved by culture of tissue and bone biopsy samples as culturing surface swabs merely indicates which microorganisms are colonizing the ulcer/wound. Radiological investigation for osteomyelitis includes plain X-rays and MRI. Antibiotic therapy is usually the first line of treatment although a multidisciplinary team approach including vascular and general surgeons may be invaluable. Surgical involvement is required for debridement, drainage of abscess and/or amputation in chronic osteomyelitis.

Gas gangrene

This is rarely seen in civilian practice and is typically associated with the battlefield. Clostridium perfringens, a spore-forming anaerobic bacterium normally found in soil and faeces, is the main cause; other species include Clostridium novyi and Clostridium septicum. Patients become rapidly and profoundly septic as exotoxins lead to rapidly spreading muscle necrosis with overlying skin discolouration, oedema and crepitus (Fig. 4.6). Even with urgent wide surgical excision of all necrotic tissue and high-dose antibiotics (penicillin and metronidazole) the disease still carries a high mortality.

Fig. 4.6 Gangrene developing in the foot of a diabetic.

(Courtesy of Mr A.S. Whyte FRCS.)

Infections following trauma

Risk of infection will be related to the amount of tissue damage and contamination with extraneous material (e.g. soil, clothing, etc). Heavily contaminated wounds need thorough cleaning and debridement of all non-viable tissue; failure may lead to severe infections including gas gangrene. A short course of broad spectrum antibiotics have been shown to reduce the incidence of early infection in open limb fractures. It is essential to determine the patient’s tetanus immunization status.

Tetanus

This is caused by Clostridium tetani, a spore-forming anaerobic organism which enters the body through soil or animal faecal contamination of a wound, injury or burn and then multiplies anaerobically in tissues, if the wound is not adequately cleaned or debrided. The incubation period varies from 4 to 21 days. Tetanospasmin (a neurotoxin) spreads along nerves from the site of infection and causes generalized rigidity and spasm of skeletal muscles. The muscle stiffness usually involves the jaw (lockjaw) and neck and then becomes generalized. The mortality ranges from 10 to 90%, being highest in infants and the elderly. Antibiotic treatment is with penicillins or, for penicillin allergic patients, clarithromycin but is only an adjunct to correct surgical care of wounds and further specialized medical treatment. Tetanus can be prevented by immunization. In the UK, all young children are offered the tetanus vaccine as part of the routine NHS childhood vaccination programme (www.nhs.uk/conditions/Tetanus); current advice is to have five doses over a life time. For non-immune individuals who have suffered a tetanus-prone injury, Human Tetanus Immunoglobulin (HTIG) is given to provide immediate protection together with wound debridement, active immunization and antibiotic treatment.

Healthcare associated infections (HCAI)

In 2006 a survey of 190 acute hospitals in England showed that 8.2% of patients had developed a HCAI (previously known as a nosocomial infection), most commonly SSI, GI infections, UTI, and pneumonia. The UK Health Act of 2006 (revised 2008) places a legal duty on hospitals to do all they can to minimize the risk of HCAI. The hospital infection control team are most closely involved in the design and delivery of the HCAI programme and will liaise with the microbiology laboratory to ensure that infections caused by important pathogens are identified at an early stage and that trends in antibiotic resistance are monitored. However, all staff members and students have a duty to take responsibility for this very important aspect of patient care. In recent years, there has been a national focus on reducing MRSA and C. difficile infections in England using a multi-faceted approach; Figure 4.7 shows the successful reduction in England of MRSA bloodstream infections (bacteraemia) from 2006 to 2010 but continuing high levels of MSSA bacteraemia. Monitoring SSI is also an important quality indicator. The Nosocomial Infection National Surveillance Service (NINSS), a national programme of SSI surveillance, was established in the UK in 1997. Participation in the scheme is voluntary (except for orthopaedic surgery) but provides hospitals with useful benchmarking data for the main types of surgery. This systematic collection of infection data (surveillance) is by nurse follow-up of all patients who have undergone surgery during a given period. Surveillance nurses will inspect surgical wounds for any signs of infection and often also follow-up the patient once discharged home to detect infection. This enables the early identification of increased incidences of infection so that measures can be taken to prevent further infections. These measures could include suspension of further surgery; deep cleaning of theatres; change in antibiotic treatments and isolation of infected patients.

Fig. 4.7 Numbers of MRSA and MSSA bacteraemia (quarterly) in England, derived from HPA Surveillance Data.