Inanimate reservoirs of infection

Equipment and materials in use in hospitals often become contaminated with micro-organisms which may subsequently be transferred to susceptible body sites on patients. Gram-positive cocci, derived from skin scales of the hospital population, are found in the air, dust and on surfaces where they may survive along with fungal and bacterial spores of environmental origin. Gram-negative aerobic bacilli are common in moist situations and in fluids, where they often survive for long periods, and may even multiply in the presence of minimal nutrients. An important example of this is legionellae in hospital domestic water supplies. Awareness of the common reservoirs of environmental and contaminating hospital micro-organisms provides the basis for maintaining standards of hygiene (cleaning, disinfection, sterilization) throughout the hospital as well as good engineering and building.

Role of antibiotic treatment

At least 30% of patients receive antibiotics during their stay in hospital, and this exerts strong selective pressures on the microbial flora, especially of the gastrointestinal tract, leading to the development of antibiotic-associated diarrhoea due to Clostridium difficile (see Ch. 22), one of the commonest causes of outbreaks of hospital infection. Sensitive species or strains of micro-organisms which normally maintain a protective function on the skin and other mucosal surfaces tend to be eliminated, whereas those that are more resistant survive and become endemic in the hospital population. This may restrict the range of agents available for treatment and may lead to the transmission of plasmid-mediated antibiotic resistance into strains that show increased virulence, survival and spread within the hospital.

Airborne transmission

Infections may be spread:

Infectious agents may be dispersed as small particles or droplets over long distances (Fig. 69.1). Staphylococci survive well on mucosal secretions, skin scales and dried pus and may be redistributed in the air after initial settlement during periods of increased activity (Fig. 69.2). Gram-negative bacilli do not generally survive desiccation in air, and this route of transmission is therefore limited to conditions of high humidity such as ventilatory equipment, showers or other fine water aerosols.

Fig. 69.1 Spread of respiratory infections by droplets and droplet nuclei.

Fig. 69.2 Infection of the air with dust particles derived from nasal and oral secretions contaminating hands, handkerchief, clothing and surrounding surfaces: (A) hand soiled with secretions from lips or nose-picking; (B) clothing contaminated by hand; (C) soiled handkerchief; (D) infected dust from handkerchief; (E) dust from clothing (e.g. from near handkerchief pocket); (F) infected dust raised after settling on floor.

Contact spread

The most common routes of transmission for hospital infection are:

Human secretions as well as contaminated dust particles or fluids may be carried on thermometers, bedpans, bed-linen, cutlery or other shared items. Hands and, to a lesser extent, clothing of hospital staff serve as vectors of Gram-negative and Gram-positive infection. Procedures involving contact with mucosal surfaces, e.g. insertion of a urinary catheter, may introduce micro-organisms from the contaminated hands of the operator or from the patient’s own urethral flora into the normally sterile bladder.

Food-borne spread

Infection may originate in the hospital kitchen, or in special diets, infant feeds, kitchen or commercial supplies. Deteriorating hygiene standards may support the proliferation of flies, cockroaches and other insects or rodents which damage stored products and act as carriers of microbes.

Blood-borne spread

The accidental transmission of infections such as HIV, hepatitis B or C by needlestick or contaminated ‘sharp’ injuries has been well documented. In areas of high prevalence of these blood-borne viruses, malaria or syphilis stringent precautions should be taken to minimize transmission between patients and from healthcare workers by strict use of single-use items and screening blood products.

Self-infection and cross-infection

The interaction between different sources of infection may be illustrated by the example of a patient undergoing lower bowel surgery. Self-infection may occur due to transfer into the wound of staphylococci (or occasionally streptococci) carried in the patient’s nose and distributed over the skin, or of coliform bacilli and anaerobes released from the bowel during surgery. Alternatively, cross-infection may result from staphylococci or coliform bacilli derived from other patients or healthy staff carriers. The organisms may be transferred into the wound during operation through the surgeon’s punctured gloves or moistened gown, on imperfectly sterilized surgical instruments and materials, or by airborne theatre dust. Postoperatively, organisms may be transferred in the ward from contaminated bed-linen, by airborne ward dust or in consequence of a faulty wound dressing technique.

Of all the possible routes, by far the most likely in this example is self-infection from the patient’s own bowel flora and it is therefore against this route that most specific preventive measures in colorectal surgery are directed. Understanding of possible sources of infection and the methods available to block transmission to susceptible sites forms the basis of hospital infection control.

Cross-infection is more often caused by ‘hospital’ strains selected for characteristics of antimicrobial resistance and virulence. An important example at present is MRSA, which can be easily identified by the microbiology laboratory, which should have a system for alerting the infection control team who need to collect the following basic epidemiological data:

The clustering of cases according to a common surgical team or location in the ward may suggest a common source and may be the first firm indication of an outbreak of hospital infection.

Soon after admission to hospital, individuals commonly become contaminated with the ‘hospital flora’. This has been shown with Staph. aureus in studies of patients before and during hospital treatment. Those patients who need to stay longer in hospital, e.g. those requiring intensive care or the elderly, are more susceptible to infection and the risks of HAI are greater.

Infection control policy

The establishment of an effective infection control organization is the responsibility of good management of any hospital. There will normally be two parts:

The functions of this team include surveillance and control of infection and monitoring of hygiene practices, advising the infection control committee on matters of policy relating to the prevention of infection and the education of all staff in the microbiologically safe performance of procedures. The infection control nurse is a key member of this team. Close working links between the microbiology laboratory, infection control nurse and the different clinical specialties and support services (including sterile services, laundry, pharmacy and engineering) are important to establish and maintain the infection control policy, and to ensure that it is rationally based and that the recommended procedures are practicable. It is important for all members of the committee to ensure that everyone in the organization makes infection control and hospital hygiene their business. Campaigns should be launched locally raise the profile of proven methods of control such as hand washing. Some of the control measures in which the infection control team should be involved are shown in Figure 69.3.

Fig. 69.3 Control measures to reduce exogenous hospital-acquired infection.

Decontamination and sterilization

The provision of sterile instruments, dressings and fluids is of fundamental importance in hospital practice. Items that are reused for procedures in normally sterile sites, such as surgical equipment, must be decontaminated by thorough washing before sterilization by heat. High-vacuum autoclaves have become accepted hospital practice. The development of these sterilizers for processing wrapped goods facilitated the provision of a centralized service of sterile supply to wards, complementing the existing theatre service. The availability of a wide range of prepacked single-use items (syringes, needles, catheters and drainage bags) sterilized commercially by γ-irradiation or ethylene oxide has further improved aseptic procedures and removed the need for reprocessing items that are difficult to clean and therefore impossible to sterilize. The scientific basis of sterilization is mentioned in more detail in Chapter 4.

Most fluids for topical use or intravenous administration are now prepared commercially or in regional units where standards of quality control and efficiency for bulk processes are more readily achieved than in individual hospital pharmacies.

Aseptic techniques

The provision of sterile equipment will not prevent the spread of infection if there is carelessness in its use. Wherever possible, no-touch techniques must be used, coupled with strict personal hygiene on the part of the operator. These routines are rigidly laid down in operating theatre practice and may be modified as required for other procedures such as wound dressing and insertion of intravenous catheters.

Cleaning and disinfection

The general hospital environment can be kept in good order by attention to basic cleaning, waste disposal and laundry. The use of chemical disinfectants for walls, floors and furniture is necessary only in special instances, such as spillages of body fluids from patients with blood-borne virus infections. Ward equipment such as bed-pan washer/disinfectors and dishwashers should be monitored to ensure reliable performance, and cleaning materials such as mop-heads and cloths should be heat-disinfected and stored dry after use. Pre-cleaning of contaminated instruments and equipment, preferably by means of an automatic washing process with an ultrasonicator, is an essential step before disinfection or sterilization.

Skin disinfection and antiseptics

The ease of acquisition and transfer of transient hospital contaminants, particularly staphylococci and Gram-negative bacilli on the hands of staff, is an important factor in the spread of hospital infection. Thorough handwashing after any procedure involving nursing care or close contact with the patient is essential. Alcohol-based hand antiseptics or ‘rubs’ have been introduced in wards where routine handwashing with water and detergent is not practicable. Gloves may be worn for many dirty contact procedures, such as emptying a urinary drainage bag or bedpan, although it should not be forgotten that the gloved hand may also become colonized by transient hospital flora.

Procedures for preoperative disinfection of the patient’s skin and for surgical scrubs are mandatory within the operating theatre. Dilute ‘in-use’ solutions of antiseptics may readily become colonized with Gram-negative bacteria and should be replaced regularly. Ideally, single-use preparations should be used. Restriction should be placed on the indiscriminate use of antiseptics and disinfectants by means of a disinfectant policy agreed by pharmacists, microbiologists and key users, such as theatre staff.

Decontamination and disinfectant policy

All hospitals should agree a policy to ensure all clinical staff are familiar with the agents used and procedures involved in decontamination. The policy should consider the following:

Effective implementation of the policy requires liaison and training of staff and regular updating as new methods and agents become available. Safety consideration for staff and patients require that a risk assessment is made of procedures and chemicals to minimize hazards and comply with local health and safety regulations. This includes the use of fume cupboards, air scavenging equipment and sealed washer-disinfectors. These requirements take decontamination of equipment out of small clinics into centralized sterile supply departments and increase the use of disposables in medical practice.

Prophylactic antibiotics

Widespread and haphazard use of antibiotics hastens the emergence of antibiotic-resistant bacteria and increases both the incidence of toxic side-effects and the cost of treatment. However, rational antibiotic prophylaxis plays an important role in infection control. Specific indications include perioperative prophylaxis in gastrointestinal and gynaecological surgery directed predominantly against anaerobic infection and for patients known to have bacteriuria at the time of urological surgery or instrumentation, directed against the urine isolate. An antibiotic policy which limits the choice of broad-spectrum agents is important both for prophylaxis and treatment (see Ch. 67).

Protective clothing

Different activities within the hospital require different degrees of protection to staff and patients. In operating theatres the wearing of sterile gowns, gloves, head gear and face masks minimizes the shedding of micro-organisms. The properties of fabrics available for theatre use have improved, and now include close-weave ventile fabrics that are comfortable to wear and allow evaporation of moisture. ‘Total protection’ of the operating site may be considered for certain high-risk clean surgery such as hip replacements, during which the surgical team may wear exhaust-ventilated suits and operate under conditions of ultraclean laminar airflow.

For many ward procedures in which there may be soiling, or for simple barrier nursing of patients with communicable diseases, plastic aprons and gloves are used. Gloves, face masks and goggles are also indicated for specific procedures when blood contact is likely through splashes or aerosols, such as dental procedures. These should conform to international standards and staff should be trained in their use and disposal.

Isolation

The isolation policy should list facilities and procedures needed to prevent the spread of specific infections to other patients (source isolation) and to protect susceptible or immunocompromised patients (protective isolation). Effective isolation demands a highly disciplined approach by all staff to ensure that none of the barriers to transmission (airborne, direct and indirect contact) are breached. Multi-bedded rooms may be used, and even wards converted during hospital outbreaks, but the simplest solution wherever possible is to use single rooms.

‘Cubicle’ isolation, by which the patient is nursed alone in a room separated by a door and corridor from other patients, confers a substantial measure of protection. Preferably, each isolation room has its own toilet and washing facility. Clean, filtered air is supplied to the room, which should be at negative pressure (exhaust-ventilated) to the corridor for source isolation or at positive pressure (pressure-ventilated) to the corridor for protective isolation. If, however, there is a small airlock vestibule separating the room from the outer corridor, then exhaust ventilation of the airlock will give effective isolation for either situation. The vestibule or lobby should contain a wash basin and include space for gowning and equipment.

In some critical situations such as bone marrow transplant units, where airborne contamination with environmental fungal spores is a problem, the efficiency of air filtration may be increased and laminar airflow maintained as a barrier around the patient. Stringent isolation in a plastic tent isolator is required only for patients with highly contagious infections and such contingencies usually require transfer to a specialist hospital.

Hospital building and design

The routine maintenance of the hospital building is important, ensuring that surfaces wherever possible are smooth, impervious and easy to clean. Major rebuilding works on or near the hospital site may generate dust containing fungal and bacterial spores, with implications for specialized units serving immunocompromised patients. Close communications with the works department and hospital administration are necessary to coordinate any protective action. When a new hospital or modification of existing building is planned, the infection control team should be closely involved in discussing the plans. In many countries, guidance on new building design exists to minimize potential hospital-acquired infection. Areas requiring special attention include operating theatres, kitchens, acute wards, laboratories and air-conditioning systems. The risk of Legionnaires’ disease is reduced by regular flushing all outlets and installing water supplies that circulate below 20°C for the cold and above 60°C for the hot circuit.

Equipment

Any object or item of equipment for clinical use should be assessed to determine the appropriate method, frequency and site of decontamination. Wherever possible, heat processes are preferred, although this may be precluded for certain thermolabile items such as fibreoptic endoscopes. Dedicated washer-disinfectors in sealed units are necessary for these items. In many situations, especially in community settings, disposable instruments should be used, although monetary and environmental costs need to be balanced against availability and transport of the item.

Personnel

An occupational health service should screen staff before employment for serious communicable diseases, such as tuberculosis, and check their immunization status. Hepatitis B vaccine should be given to all health care workers if they have not been fully immunized. Those at special risk performing exposure-prone procedures, such as invasive surgery, should be screened for blood-borne viruses. All healthcare staff (including students and those working in the community) should receive occupational health advice and protection. Staff who have contracted infections such as impetigo or diarrhoea should report and be screened if necessary. Those that sustain needlestick injuries from potentially contaminated sources should have access to advice and post-exposure prophylaxis with antivirals and immunization. There should be an educational programme tailored to the needs of different cadres of staff both on induction and as part of continuing professional development.

Monitoring

Routine microbiological sampling of the environment is of little benefit, although monitoring of the physical performance of air-conditioning plants and machinery used for disinfection and sterilization is essential. In the event of an outbreak of hospital infection such as Legionnaires’ disease, more specific monitoring targeted at the known or likely causative micro-organism should be considered.

Microbiological screening of staff or patients is not undertaken routinely, but it may be needed for specific purposes: to detect carriers of MRSA and hepatitis viruses in those performing some types of surgery or where transmission to patients has occurred.

Surveillance and the role of the laboratory

The detection and characterization of hospital infection incidents or outbreaks rely on laboratory data that alert the infection control team to unusual clusters of infection, or to the sporadic appearance of organisms that may present a particular infection risk or management problem. This is sometimes referred to as the ‘alert organism’ system. Bacterial typing schemes and antibiograms (see Ch. 3) are very important in this regard. In some situations mandatory surveillance of cases of infection with particular pathogens such as MRSA or C. difficile may be useful to compare hospitals or units and reduce hospital infection by regular, timely feedback to clinicians and managers. Regular visits to the wards are also important to record data on infected patients from whom no specimens have been received and to respond to problems as they occur. Such visits also serve to provide opportunities for practical teaching, which is another important element of the infection control team’s responsibility. Advances in surgical practice have lead to short stays in hospital so that some postoperative infections are only detected after discharge. Surveillance of surgical site infection should include data collected post-discharge.