Healthcare associated infections
February 2006
Appendix
Summary information on the micro-organisms causing HCAIs that are of particular significance:
Staphylococcus aureus
This Gram-positive bacterium frequently colonises human skin and mucosa and is found in up to 30 per cent of the population. S.aureus is a common cause of food poisoning as well as skin and wound infections, urinary tract infections, pneumonia and bacteraemia. S.aureus is a major cause of HCAIs but most strains are sensitive to many antibiotics, and infections can be effectively treated. Some S.aureus strains have developed resistance to conventional antibiotics, including methicillin, and are known as methicillin-resistant Staphylococcus aureus (MRSA). Effective treatment for MRSA infections is usually with the glycopeptide antibiotics vancomycin or teicoplanin. However, the emergence of vancomycin resistant Staphylococcus aureus (VRSA) is causing concern.
Glycopeptide-resistant enterococci (GRE)
Enterococci are bacteria found in the faeces of humans and many animals and they commonly cause urinary tract infections and wound infections as well as bacteraemia, and occasionally endocarditis and meningitis. Enterococci frequently colonise open wounds and skin ulcers. Minor infections can be treated by common antibiotics. However, only aminopenicillins, or teicoplanin and vancomycin are reliably effective against serious enterococcal infections. Enterococcus faecalis and Enterococcus faecium have emerged as leading nosocomial pathogens in recent years. Enterococci are among the most antibiotic resistant bacteria isolated from humans. GRE, and in particular vancomycin resistant enterococci (VRE), have emerged as major nosocomial pathogens as they are typically resistant to multiple antimicrobials and treatment is extremely difficult, often limited to linezolid.
Clostridium difficile
This is a Gram-positive, spore-forming bacterium that is present in the natural flora of the gut in up to 3 per cent of healthy individuals. C.difficile causes illness when the ‘normal’ bacteria in the gut are disturbed by certain antibiotics. Through the production of toxins, C.difficile can cause diarrhoea which may be mild and resolve once antibiotic treatment ceases, or it can cause more severe colitis and life-threatening colitis with or without pseudo-membrane formation. The elderly are most at risk with over 80 per cent of cases reported in the over 65 years age group. Immuno-compromised patients are also at risk. The micro-organism produces spores that can exist in the environment and may be transmitted from patient to patient or via healthcare workers.
Streptococcus pneumoniae
This Gram-positive bacterium colonises the nasopharyngeal mucosal epithelium and is a major cause of community-acquired pneumonia (CAP), invasive pneumococcal disease (IPD) and bacterial meningitis. Individuals principally affected are those at the extremes of age (children and the elderly), individuals without a functioning spleen, and immuno-compromised patients. Many strains of S.pneumoniae have become resistant to some of the antibiotics used to treat pneumococcal infections, and resistance to penicillin is common in some parts of the world.
Acinetobacter species
Acinetobacter is a type of bacterium carried by 25 per cent of healthy people and readily isolated from many sources in the environment, including drinking and surface waters, soil, sewage and various food types. There are at least 25 different Acinetobacter species, though it is mainly Acinetobacter baumannii that causes infections in hospital patients. Such infections can include skin and wound infections, urinary tract infections, pneumonia and bacteraemia. These 'hospital-adapted' strains of Acinetobacter are often resistant to antibiotics and may be difficult to treat and to eradicate; for example from intensive care units. Strains resistant to carbapenems have been reported in UK hospitals, leaving polymixin as the only licensed antibiotic available for treatment.
ESBL (Extended-Spectrum Beta-Lactamase) producing Escherichia coli
ESBL-producing E. coli are antibiotic resistant strains of E. coli. Although E. coli normally resides harmlessly in the gut, it is one of the most common bacteria causing infections in humans – particularly urinary tract infections (UTIs) – in the community as well as in hospitals. These infections can sometimes progress to cause more serious infections such as blood poisoning which can be life threatening. ESBL strains of E. coli produce an enzyme called extended-spectrum beta-lactamase, which makes them more resistant to antibiotics and the infections harder to treat. Most ESBL-producing E. coli are resistant to cephalosporins, penicillins, fluoroquinolones, trimethoprim, tetracycline and some other antibiotics, leaving very limited options for oral treatment in the community. In many instances, only two oral antibiotics (nitrofurantoin and fosfomycin) and a very limited group of intravenous antibiotics remain effective. Most ESBL-producing E. coli infections occur in people with other underlying medical conditions and in elderly people. Patients who have been taking antibiotics or who have been previously hospitalised are mainly affected. Further research is needed to look at the risk factors associated with different strains of ESBL-producing E. coli and how they are transmitted between patients and in community settings.
Candida species
The yeast Candida is the most common cause of opportunistic mycoses worldwide. It is a member of the normal flora of the skin, mouth, vagina, and stool, and is commonly found in the environment, particularly on leaves, flowers, water, and soil. The genus Candida includes around 154 species, of which six are most frequently isolated in human Candida infections including Candida albicans, Candida tropicalis, Candida glabrata, Candida parapsilosis, Candida krusei, and Candida lusitaniae. Infections caused by Candida spp. are in general referred to as candidiasis. The clinical spectrum of candidiasis is extremely diverse and almost any organ or system in the body can be affected. It can cause either benign and frequent infections such as oral and vaginal candidiasis or more serious problems such as life-threatening invasive infections in immuno-compromised hosts. C. albicans is the most pathogenic and most commonly encountered species and accounts for 60 per cent of all Candida infections. It can grow as a biofilm on artificial surfaces including medical implant devices such as catheters, prostheses, artificial valves and joints, and dentures. Several anti-fungal drugs are effective against candidiasis, of which the most effective is fluconazole. The emergence of strains of C. albicans resistant to fluconazole increases the difficulty in treating the infection and necessitates the use of other anti-fungal drugs that are less effective or have damaging side effects (eg amphotericin).
Norovirus
Noroviruses are a group of viruses that are the most common cause of gastroenteritis in England and Wales and estimated to affect between 600,000 and one million people in the UK each year. Although relatively mild, norovirus gastroenteritis can occur at any age as prior infections do not elicit long-lasting immunity. The incubation period is usually 24 to 48 hours and symptoms last between 12 and 60 hours. The symptoms can include the sudden onset of nausea followed by projectile vomiting, and watery diarrhoea. Some people may have a raised temperature, headaches and aching limbs. The majority of people make a full recovery, however some (usually the very young or elderly) may become very dehydrated and require hospital treatment. Norovirus spreads very easily from one person to another and can be transmitted by contact with infected individuals, by consuming contaminated food or water, or by contact with contaminated surfaces or objects. As the virus is easily spread from one person to another and can survive in the environment for many days, outbreaks of norovirus gastroenteritis are common in semi-closed environments such as hospitals, nursing homes and schools. The most effective way to respond to an outbreak is to isolate those infected for up to 48 hours, disinfect contaminated areas, institute good hygiene measures including hand-washing and provide advice on food handling. There is no specific treatment for norovirus; however it is a self-limiting infection and recovery occurs within one to two days.