Healthcare-Associated Infections-Definitions and Range

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Chapter: Pharmaceutical Microbiology : Public Health Microbiology: Infection Prevention And Control

HCAIs encompass a considerable variety of infections of different body sites and systems caused by a wide range of bacteria and some viruses and fungi. The types of infection reflect all the body sites and systems that can be the subject of medical intervention.



HCAIs encompass a considerable variety of infections of different body sites and systems caused by a wide range of bacteria and some viruses and fungi. The types of infection reflect all the body sites and systems that can be the subject of medical intervention.


Wound And Soft Tissue Infections


Any wound, accidental or surgical, breaches one of the key barriers to infections—the skin. With accidental wounds, contamination with dirt, soil and environmental bacteria may be inevitable, but with ‘deliberate’ surgical wounds, every effort must be made to minimize the risk of postoperative wound/surgical site infection (SSI; the term reflects the importance of infection at any part of the surgical site, not only the obvious external wound). These SSIs may come from the patient’s own normal body flora (e.g. from the intestinal bacteria after abdominal surgery), from nose or skin carriage of wound pathogens such as Staphylococcus aureus by the patient, or by cross-infection from other patients or staff as a result of a breakdown of aseptic procedures and proper clinical care. Protocols for clinical care of surgical wounds aim to minimize the risk of the cross-infection, and antibiotic prophylaxis combined with careful surgical practice aims to minimize the risk from the patient’s own endogenous bacteria.


Non-surgical soft tissues sites are also prime sources of HCAI, particularly peripheral ulcers (vascular, diabetic, etc.) and pressure sores (decubitus ulcers) where the initial vascular insufficiency and tissue breakdown provides an ideal environment for bacterial infection.


Bloodstream Infections


Potentially the most severe types of HCAI in terms of outcome are bloodstream infections (bacteraemias). The blood and the cardiovascular system should be sterile and the presence of bacteria in the blood is an alarm signal for a patient’s healthcare. Many bacteraemias are part of infectious diseases not linked to healthcare risks (bacterial meningitis, community acquired pneumonia, acute pylonephritis) but others are important complications of healthcare. Almost all hospital treatment in modern medical practice requires invasive procedures with the insertion of various synthetic tubes and prosthetic devices. The insertion of indwelling intravascular catheters and cannulae penetrates the protective layer of the skin and provides a portal of entry for bacteria. Central venous catheters are used increasingly for a range of clinical investigations and treatments and carry a significant risk of infection which starts on the artificial surface of the catheter and then seeds the bloodstream more generally, with the risk of clinical sepsis and infection of cardiovascular structures such as the heart valves (endocarditis) or other metastatic infection sites. Short peripheral intravenous cannulae carry less individual risk of infection, but so many are used in modern clinical practice that they are in fact the source of more HCAI bacteraemias than central catheters. Other local sites of HCAI (wounds, ulcers, urinary tract, respiratory tract) can also lead to bacteraemia.


Urinary Tract Infections


The commonest form of HCAI (see below) are urinary tract infections, mostly as a result of indwelling urinary catheters which inevitably become contaminated and colonized with bacteria, then leading to infection of the bladder and the lower urinary tract, then the ureters and potentially the kidneys (pylonephritis). This can be an important cause of bacteraemia.


Respiratory Tract Infections


Respiratory infections are some of the most common types of infection in the general community and these can also affect hospital patients, but some clinical conditions and treatments predispose patients to healthcare associated respiratory tract infections. During the postoperative period surgical patients are particularly vulnerable to pneumonia; they will have undergone endotracheal intubation for their anaesthesia and postoperative discomfort and inactivity may lead to inadequate ventilation of their lungs and inability (or disinclination) to cough, resulting in postoperative pneumonia. This risk is greatly magnified in patients needing intensive care and undergoing prolonged intubation and artificial ventilation. Ventilator-associated pneumonia (VAP) is one of the major challenges to successful intensive care. As well as the local effects of VAP on the respiratory tract, it is also a significant cause of bacteraemia.

Gastrointestinal Tract Infections


Infectious diarrhoea is a well-recognized community syndrome. Some of the issues that result in diarrhoea and vomiting in the population at large, such as mass catering leading to food poisoning with Salmonella and Campylobacter spp. also apply in hospitals and other healthcare and social care settings but other gastrointestinal infections cause particular problems in relation to healthcare settings. Norovirus vomiting and diarrhoea spreads so readily in closed communities that it causes numerous and frequent outbreaks in all health and social care settings and is the commonest cause of ward closures in the NHS in England to control the spread of this virus. One bacterial cause of potentially severe, indeed fatal, diarrhoeal disease that is much more specifically an HCAI is Clostridium difficile infection (CDI). This infection generally affects only those whose normal gut bacterial flora has been disturbed by treatment with broad spectrum antibiotics (or some other infection proven or suspected) which enables the Cl. difficile spores to germinate and then the vegetative bacteria to produce their damaging toxins.


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