A healthcare-associated infection (HCAI) is defined as any infection that occurs in the course of a patient’s treatment in a hospital or healthcare facility, but which was not present or incubating at the time of the patient’s admission. It also includes infections that are acquired in hospital, but that do not become apparent until after discharge, as well as occupational infections that are acquired among healthcare staff.
According to the Health Protection Agency 2012, the six most common HCAIs are:
Most public or private healthcare providers take healthcare-associated infections very seriously. Depending on the provider they be regarded as 'significant harm events'. Modern healthcare providers are focusing on rapid diagnosis in order to provide effective treatment and to inform their infection control strategies.
Patients who are most at risk of contracting an HCAI include the elderly or very young, patients admitted to an intensive care unit, long term in-patient stays, the use of invasive surgical devices or immunosuppression due to surgery or trauma or treatment.
Alert organisms or alert conditions are a specified list of microorganisms/infections which on identification must be referred to a suitably qualified Infection Prevention and Control nurse (IPCN) for investigation. This investigation may also require a root cause analysis (RCA) to establish the index case of infection and the like vectors of transmission.
Typical alert organisms may include:
MRSA is a type of bacteria that's resistant to several widely used antibiotics. This means infections with MRSA can be harder to treat than other bacterial infections. The full name of MRSA is meticillin-resistant Staphylococcus aureus, you might also have heard it called a 'golden staph' because often the infected pus is yellow/gold in colour.
MRSA lives harmlessly on the skin of around 1 in 30 people, usually in the nose, armpits, groin or buttocks. This is known as "colonisation" or "carrying" MRSA and does not normally cause any symptoms.
However, people staying in hospital are most at risk of developing an MRSA infection because:
Clostridium difficile, also known as C. difficile or C. diff, is bacteria that can infect the bowel and cause diarrhoea. The infection most commonly affects people who have recently been treated with antibiotics but it can spread easily to others.
Patients have and increased risk of acquisition if they:
C. difficile bacteria are found in the digestive system of about 1 in every 30 healthy adults and often live harmlessly because other beneficial bacteria in the bowel keep it under control. Some antibiotics can interfere with the balance of bacteria in the bowel, which can cause the C. difficile to multiply and produce toxins that make the patient ill.
When this happens, the patients' diarrhoea contains the C. difficile bacteria which can easily be spread in the environment or on the equipment within the hospital facility. Once out of the body, the bacteria turn into resistant cells called spores which can survive for long periods on hands, surfaces (such as toilets), objects and clothing unless they're thoroughly cleaned and decontaminated.
CPE is an acronym for a group of bacteria known as carbapenemase-producing Enterobacteriaceae, also know as CRO (Carbapenem resistent organism) or CRE (Carbapenem resistent Enterobacteriaceae). Enterobacteriaceae are bacteria that usually live harmlessly in the gut of humans, often known as colonisation. However, if the bacteria get into the wrong place, such as the bladder or bloodstream, they can cause infection.
Personal hygiene and cleanliness of the hospital environment and equipment is extremely important in preventing the CPE infections spreading. Important areas to pay attention to are:
VRE is an acronym for vancomycin-resistant enterococci. Enterococci are bacteria that can live in the gastrointestinal tract of most healthy people without causing an illness. Vancomycin is an antibiotic used to treat infections caused by enterococci and when enterococci become resistant to vancomycin they are called vancomycin-resistant enterococci (VRE).
Sometimes VRE can get into other parts of the human body and cause an infection. Patient groups most at risk of getting a VRE infection usually have a reduced immunity due to another treatment they are undergoing such as:
Acinetobacter species belong to a group of Gram-negative bacteria that are readily found throughout the environment including drinking and surface waters, soil, sewage and various types of foods. Healthy individuals are at low risk of infection by Acinetobacter species. Acinetobacter infections acquired in the community are very rare and most strains found outside hospitals are sensitive to antibiotics.
A few species, particularly Acinetobacter baumannii, can cause serious infections in hospital patients who are already very unwell. These ‘hospital-adapted’ strains of Acinetobacter baumannii are sometimes resistant to many antibiotics and the infections that they cause can therefore be difficult to treat.
The application of, and compliance with, infection prevention and control (IPC) in hospitals is crucial to the effective management of patient care. Most healthcare providers have established experienced teams of suitably trained nursing staff (infection prevention nurse or IPN) and consultant medical experts to create and deliver the infection prevention and control strategy for the organisation.
The IP&CT’s responsibilities include: providing evidence-based best practice advice; ensuring the safety of patients, staff, the general public and the environment; authoring the annual IP&C report; and ensuring compliance with the relevant code of practice.
To prove compliance with the code of practice most hospitals will need to demonstrate the following:
The role of the human immune system is to prevent the invasion of microorganisms such as bacteria, fungi, viruses and protozoa.
How successful the immune system is, depends on its ability to distinguish between ‘self ‘antigens (molecules that belong on the cell’s surface) and ‘non-self’ antigens (foreign cells or microorganisms that are invading the host).
When the immune system recognises as antigens as being ‘non-self’ it initiates the innate immune response.
The innate immune response is present from birth and is the first line of defence against infection. It is a nonspecific response, however, which means it does not provide long-lasting immunity.
Mechanical defence mechanisms of the innate immune response:
Biochemical defence mechanisms of the innate immune response:
The actions of the innate immune response are often sufficient to destroy invading microorganisms.
The acquired immune response is the secondary immune response which comes into play when the innate immune response has failed to destroy an invading microorganism.
It is highly specific, it is able to respond to virtually any antigen it has previously come across and it retains a memory of these previous encounters - which helps to prevent the body being reinfected with the same microorganism.
However, while the acquired immune response is highly effective, it is much slower than the innate immune response - sometimes taking up to 10 days to fully mobilise.
Macrophages and lymphocytes (branch-like cells found in the skin) play a key role in the activation of the acquired immune response.
When a foreign antigen enters the body it will eventually come into contact with a lymphocyte with a matching receptor.
The cell with the ‘best fit’ will then divide to produce a large number of clones which will attack the microorganism.
There are three groups of antigen receptor cells which contribute to the acquired immune response:
T and B lymphocytes - which have unique antigen receptors that provide specific immunity (B cells also produce soluble antigen receptors, or antibodies, which react specifically with the antigen that has stimulated their production)
Major histocompatibility complex (MHC) - a group of antigen receptors, found in all vertebrates, that function by presenting antigenic peptides to the T cells
The complement system plays a major role in the acquired immune response by:
It can be activated by the lectin pathway, the mannan-binding lectin (MBL) pathway or the classical pathway.
Because the acquired immune system is an anticipatory system, it can sometimes generate ‘anti-self’ receptors which trigger autoimmune diseases (Graves disease, Type 1 diabetes, Guillain-Barre syndrome, Celiac disease etc)
The formation of attenuated (weaker forms of) ‘live’ vaccines provides a way for a less virulent form of a microorganism to trigger an immune response. The aspect of ‘memory’ also means that when a similar or identical antigen is encountered, the immune response is faster and more expansive.
The isolation of organisms within a laboratory is reliant on the creation of a setting that mimics the normal conditions under which that cell would normally grow whether in its host or in the environment.
The goal of culturing bacteria in the laboratory is to grow a population of cells (or colony) that is 20-30 divisions of a single cell.
The rate of bacterial growth is dependent on several factors:
The first stage in processing a clinical specimen is the inoculation of either a solid or liquid culture medium:
Bacterial classification is key to determining the appropriate antibiotic therapy. So once an organism has been cultured it will need to be identified. Because bacteria are naturally colourless, Gram staining is used to identify differences in the bacterial cell wall.
The specimen is first transferred, and heat fixed to a glass slide., before being covered with blue dye (crystal violet) which is washed off after thirty-seconds and decolourised with acetone. The acetone is then removed and a red dye (safranin) is applied for one minute. The slide is then washed and blotted dry.
If the bacteria are Gram-positive they will stain blue-black.
If they are Gram-negative they will stain red-pink.
The high lipid content of the bacterial cell wall of mycobacteria means they cannot be Gram-stained, but will instead need to be identified using the Ziehl-Neelson staining method.
To test for antibiotic susceptibility, bacterial colonies are isolated from the culture plate and inoculated onto a new agar plate.
Antibiotic-impregnated paper discs are then placed onto the plate and immediately begin to diffuse into the agar.
Bacteria that are susceptible to antibiotics will form a zone of inhibition around the disc. Those that are resistant will grow right up to the edge.
Identifying the genus and species of bacteria, and differentiating between different strains, is carried out in a specialist PHE Reference Laboratory. Typing techniques can also be used to determine the evolution of the strain and any emerging pathogens or clones
An antibiotic is defined as a microorganism that is effective in killing (bactericidal) or inhibiting (bacteriostatic) the growth of another microorganism. The term antibiotic originally applied to naturally occurring organisms such as penicillin, however it now also includes the manufacture of synthetic and semi-synthetic antibiotic compounds.
Antibiotics are used in the treatment of bacterial infections. ‘Microbial agents’ are any natural or synthetic agents used to treat a range of infections including bacteria, viruses, fungi, parasites and worms.
Therapeutic drug monitoring (TDM) is used to determine the trough levels (the level of drug in the bloodstream) over the course of treatment. If the trough level is too high the antibiotic will be toxic to the patient - if it is too low this can indicate a missed dose, a prolonged period between doses or an insufficient therapeutic dose.
The key characteristics of antibiotics are:
The choice of antibiotic and how it is administered depends on the organism and its sensitivities, the site of infection and the patient history. Intravenous antibiotics, for example, may be required for the treatment of systemic infections or in cases where the patient cannot tolerate the drug orally.
Antibiotics can act in the following ways:
The discovery of penicillin, and the development of antimicrobial agents, have transformed the way in which infections and infectious diseases are treated.
However the growing global issue of antimicrobial resistance - the ability of a microorganism to thrive in the presence of an agent that would normally kill it or inhibit its growth - presents a major challenge to modern healthcare.
The first signs of antimicrobial resistance were identified just ten years after the initial mass production of antibiotics, when strains of Staphylococcus aureus were found to have developed resistance to penicillin. The first reported case of Meticillin-resistant Staphylococcus aureus (MRSA) was reported in 1963.
Antimicrobial resistance can be inherent (ie when it is part of the organism's genetic makeup) or it can be acquired (developing naturally over time due to a genetic mutation or recombination).
The overuse and misuse of antibiotics is a significant contributor to the rise of antimicrobial resistance including:
Antimicrobial resistance is affected by a variety of factors in the hospital or healthcare environment including:
Antimicrobial resistance is a complex global problem that affects not only human health but also animal health, welfare and security.
In 2013, the UK’s Department of Health (DH) together with the Department for Environment, Food and Rural Affairs (DEFRA) formulated a five-year antimicrobial resistance strategy.
The strategy targets 7 key areas:
The responsible use of antibiotics in livestock is also acknowledged as being key to tackling the challenge of antimicrobial resistance.
In November 2018, the UK Government announced the establishment of an International Reference Centre for Antimicrobial Resistance, with the aim of reducing the use of antibiotics in animals by 25% by 2020.
Healthcare acquired infections (HCAIs) are the result of sequence of events that take place between an infectious agent (or pathogen), a host and an environment. This process is known as the 'chain of infection' and is comprised of six ‘links’.
Infectious agents or pathogens include:
How well any pathogen is able to thrive depends on three elements:
The reservoir is the principal environment in which a pathogen is able to live, flourish and multiply.
Common reservoirs for infectious agents include humans, animals, insects and the environment.
In humans, there are two forms of reservoir: acute clinical cases (in which someone is infected and is displaying signs and symptoms of the disease); and carriers (in which an individual has been colonised with an infectious agent but is not feeling unwell.)
Acute clinical cases are more likely to be diagnosed and treated - and the patient's contacts and normal activities will normally be restricted.
Carriers can present more of a risk to those around them because they don’t exhibit any signs or symptoms of illness.
Carriers can be further divided into four types:
Examples of animal or insect reservoirs include:
Any infectious disease that is transmitted under natural conditions from animal to human is referred to as zoonosis.
The environment contains multiple reservoirs of infection including soil (which can act as a reservoir for Clostridium tetani, the causative agent of tetanus) and water (which is a reservoir for Legionella pneumophila, the causative agent of Legionnaires disease).
The portal of exit is the route by which a pathogen is able to leave the reservoir or host.
In humans the key portals of exit are:
An infection can be transmitted from its reservoir to a susceptible host both directly and indirectly.
Direct transmission is generally instantaneous and takes place when there is direct contact with the infectious agent. Examples of direct transmission include: tetanus, glandular fever, respiratory diseases and sexually transmitted diseases.
Indirect transmission can occur through animate means (such as fleas, ticks, flies or mosquitoes) or via inanimate means (such as food, water, biological products or surgical instruments). Indirect transmission can also be from contact with a contaminated surface, airborne, when tiny particles of an infectious agent are carried by dust or droplets in the air and inhaled into the lungs.
The portal of entry is the means by which an infection is able to enter a susceptible host.
Portals of entry into the human body include:
How susceptible any host will be depends on:
The healthcare environment can expose patients to infection risks that they may not encounter elsewhere. Understanding how infections become established, and how they are transmitted, is vital for effective infection prevention and control.
The breaking or disrupting of the chain can be achieved at any link: through rapid and accurate diagnosis; prompt treatment of infected patients; safe disposal of waste; sterilisation and disinfection of medical equipment and the implementation of an environmental decontamination strategy.
Environmental cleaning and disinfection are crucial to the prevention and control of infection within hospitals and healthcare facilities.
Pathogens and multidrug resistant organisms can easily be shed from infected or colonised patients and have been known to survive on dry surfaces for hours, days or even months at a time.
There is growing evidence that contaminated surfaces are a key contributor to the transmission of person-to-person healthcare associated pathogens. And an estimated 20% to 40% of HCAIs are spread via the hands of healthcare workers.
Decontamination is the series of processes that are used to remove or destroy infectious agents and organic matter in order to prevent the spread of infection.
The first stage of decontamination is cleaning - or the physical removal (whether manual or automated) of dirt, dust and soil from surfaces. In healthcare environments this will normally involve a combination of water, detergent, cloths and mops and will normally be performed daily.
Enhanced cleaning refers to the methods used in addition to standard cleaning, and is done in response to a specific infection prevention and control requirement.
Enhanced cleaning may involve increased frequency of cleaning - or the addition of other cleaning equipment or disinfectants.
It is routinely undertaken at the point of discharge or transfer of a patient who has been known to be infected with a pathogenic microorganism.
While manual disinfection can help to reduce the number of viable infectious agents in the healthcare environment, it is not always sufficient on its own to inactivate certain microbes such as viruses and spores. In these cases, the use of a specific concentration of a chemical agent may be required.
But while enhanced cleaning and disinfection has been proven to be successful in reducing HCAIs, studies have also shown that when cleaning is undertaken manually it is only ever partially effective - with only 50% of hospital ward surfaces being adequately decontaminated with the use of chemical disinfection.
Specialist automated technologies, for example the use of hydrogen peroxide vapour or ultraviolet light, can play a vital role in supporting the efficacy of manual cleaning practices. However these technologies can only supplement (and never replace) standard cleaning.
There is also considerable evidence of the use of self-disinfecting surfaces (such as copper coated surfaces) in decreasing the prevalence of HCAIs.
Isolating infected patients in a single room is generally considered best practice in helping to isolate the organism, control its transmission and prevent the spread of infection. It should however be implemented until a risk assessment has been conducted.
Outbreaks of infection are common in acute hospital settings and can be caused by a wide variety of microorganisms.
Public Health England (PHE) defines an ‘outbreak’ as: ‘an incident in which two or more people experiencing a similar illness are linked in time or place’. The term ‘outbreak’ can also be applied to a single case of a rare disease - such as botulism, diphtheria, polio, rabies or Ebola.
The primary objective of outbreak management is to protect public health and safety by identifying the likely source and mode of transmission and implementing infection prevention and control measures.
In a hospital setting it is crucial that an initial investigation is carried out within the first 24 hours in order to clarify the nature of the outbreak and to determine whether an outbreak control team (OCT) will need to be convened.
The OCT is responsible for agreeing a case definition, coordinating activities, conducting an investigation and ensuring that infection control measures are promptly implemented. The OCT will declare an outbreak to be over once there is no longer a risk to public health, the number of cases has declined or the probable source of infection has been identified and removed.
The pathogens that cause infectious diarrhoea can be ingested (through the consumption of contaminated food or water) or transmitted through invisible contamination via the hands. They can then be spread to other patients via the faecal-oral route.
Common causes of infectious diarrhoea include: Clostridium difficile, Giardia, Norovirus, E. coli, Campylobacter, Salmonella, Cryptosporidium, Shigella and Staphylococcus aureus.
An essential prerequisite for patient assessment is to establish the individual’s normal bowel function (consistency, frequency, type). Any pre-existing medical conditions, for example, may also mean that episodes of diarrhoea are considered normal for that patient.
A thorough history will also need to be taken to determine whether there is an infectious cause, including - the onset and duration of the symptoms, previous patient history of C. diff, associated signs or symptoms such as abdominal pain, fever or vomiting, the patient’s medical history (eg inflammatory bowel disease, abdominal or pelvic irradiation), any history of recent foreign travel, medication (antibiotics, laxatives, drugs etc), food history, recent contact with pets or farm animals.
If an assessment indicates a potentially infectious cause then the following investigations will be implemented:
Stool specimen - ideally this should be obtained within the first 48 hours of illness when the pathogen is at its most acute phase
Depending on the results of the stool culture, antibiotics may be indicated. Antidiarrheal agents should not be administered as they decrease the fecal transit time and increase the risk of toxin retention, which can cause damage to the bowel tissue.
Surgical site infection (SSI) is a wound infection which occurs after an invasive surgical procedure. It one of the most common HCAIs (accounting for around 16% of all HCAIs in England) and is a major cause of increased length of hospital stays, morbidity and mortality.
SSIs are defined using a set of standard clinical criteria according to whether they affect the superficial tissues (skin and subcutaneous layer) or the deeper tissues (deep incisional or organ space.)
The majority of SSIs are caused by endogenous infection - microorganisms (such as Staphylococcus aureus) that already present in the patient, whether on their skin (skin flora) or within an internal organ.
Exogenous infection occurs when external microorganisms contaminate the operative site. Sources of exogenous infection include surgical instruments, the theatre environment and the air. External microorganisms can also contaminate the wound at the time of an accident or following surgery before the wound has healed.
Most SSIs are preventable by applying measures at the point of pre, -intra, and post-operative phases of care.