Nosocomial Infections Flashcards
How are hospital infections acquired?
Exogenous source
Cross infection
Endogenous source
What are exogenous sources?
E.g. other patients, medical staff, from hospital environment: food, air, dust, water, catheters, instruments and equipment
What are endogenous sources?
I.e. another site within the patient
Increased incidence when patients are elderly, immunocompromised, have undergone surgery or other invasive techniques such as catheterisation
How many individuals suffer a health care associated infection and where are most people usually situated in the hospital that are most vulnerable?
About 10% of patients suffer health care associated infections (rates between 6.9-25%)
More infection in intensive care units (high dependency units)
What are some examples o nosocomial (hospital-aquired) bacterial infections?
Staphylococcus aureus Clostridium difficle Enterococcus faecalis Pseudomonas aeruginosa Staphylococcus epidermidis Klebsiella pneumonia Norovirus- winter vomiting virus
In what ways could hospital infections be prevented?
By simple hygiene precautions; disinfection, especially hand-washing by staff; isolation of patients; use of sterile equipment; appropriate use of antibiotics
Roughly how many nosocomial infections are preventable?
15-30%
What are the risk factors in obtaining a nosocomial infection?
Age Length of stay in hospital Immunocompromised status MRSA (added problem, anti-biotic resistance) C. difficile- surpass gastric acidity
What is the cost of hospital acquired infection?
Increased length hospital stay
Increased number of admissions
Increased cost of drugs required to treat infections
Increased cost associated with surveillance and implementation of control measures
Infection control teams
What are the common infections seen within a hospital?
MRSA- Methicillin (Meticillin- drug to control) Resistant Staphylococcus aureus
Staphylococcus aureus
What is Staphylococcus aureus?
Gram positive coccus Grow in grape-like clusters Golden colonies Non-fastidious, facultative anerobe Survives drying, salt-tolerant
What are the main ways Staphylococcus aureus is found and is spread by?
Commonly found in nose and on the skin of healthy humans
Spread by contact and airborne routes
What are some examples of diseases acquired in a hospital?
Food borne disease- caused by enterotoxin
Skin infections- pimples, boils, impetigo, scalded-skin
syndrome
Post-operative wound infections- catheter associated infection
Septicaemia- endocartisis (heart damage)
Osteomyelitis (bone infection)
Pneumonia
What are some of the toxins present in s. aureus infections?
Enterotoxins (vomiting, diarrhoea)
Toxic shock syndrome toxin (TSST)
‘Superantigens’, trigger cytokine release, cause ‘shock’
What are some of the cell-destroying enzymes and toxins present in s.aureus infections?
Alpha toxin
Leukocidin
Exfoliate toxin (scalded skin syndrome)
Panton-Valentine leukocidin
What are virulence factors?
Molecules produced by bacteria, fungi etc. that add to their effectiveness allowing them to colonise a host
How do anti-chemotaxis allow the staphylococcus to enter the host?
Chemotaxis inhibitory protein of staphylococci (CHIPS)
Extracellular adhesion protein (Eap)
How do anti-opsonic and anti-phagocytic allow staphylococcus to enter the host?
Staphylococcal complement inhibitor (SCIN)
Protein A (binds antibody wrong way round)
Capsule (formation of biofilms, adherence to plastic, hard to remove and treat)
Staphylokinase
Fibrinogen- binding proteins
Haemolysins and Leukocidins
What virulence factors does Staphylococcus have?
Anti-chemitaxis Anti-opsonic and anti-phagocytic Iron-uptake systems Degradative enzymes Toxins Adherence
How do degradative enzymes allow staphylococcus to enter the host?
DNAse
Lipases
Proteases
Hyaluronidase
How do toxins allow staphylococcus to enter the host?
Exfoliative toxins
(scalded skin syndrome, leuocidin, alpha toxins)
Superantigens
(toxic shock toxins and enterotoxins)
How does adherence allow staphylococcus to enter the host?
Fibronectin-binding protein
Other ECM binding proteins
MSCRAMMS- microbial surface components recognising adhesive matrix proteins- bind host proteins, may aid adherence to host tissues and serum-coated plastic
What is the resistant strain of staphylococcus and when did it emerge?
Methicilin-resistance staphylococcus aureus (MRSA) emerged 30 years ago
What gene gives staphylococcus resistant?
mecA gene
What does this mecA gene do?
Encodes mutant penicillin-binding protein (PBP2a) with lower affinity for beta-lactam antibiotics
Replaces the ‘normal’ penicillin binding proteins (enzymes involved in the peptidoglycan synthesis) to which penicillin normally targets
How is staphylococcus prevented?
Vancomycin
What is Clostridium difficile?
Gram positive rod
Strict anaerobe, spore-forming
Where is C. difficile found?
In gut of:
<1% of people outside hospitals
5-10% of hospital patients
What are the range of symptoms from C. difficile?
Mild, self-limiting diarrhoea
Severe diarrhoea and abdominal pain
Life-threatening pseudomembranous colitis
• Extensive flammation and necrosis of the colonic mucosa
What are the steps that result in death from C. difficile?
Normal colon Reduction in major genera of anaerobes C. difficile grows to high numbers Production of exotoxins A and B Diarrhoea Ulceration of colon Death
What are the symptoms due to?
Toxin A (enterotoxin) cause hypersecretion of fluid (diarrhoea)
Toxin B (cytotoxin) damage and destroy cells
A negative and B positive cause clinical disease
Both glucosyltransferases- affect actin cytoskeleton
Damage powerful chemoatractant for neutrophils
What has ribotype 027 done?
Increased severity, mortality and relapses of C. difficile
What are the treatments of C. difficile?
Discontinuation of the implicated antibiotic
Specific therapy with metronidazole or vancomycin
Why do relapses often occur in c. difficile?
Can’t restore flora in time, treated by more antibiotics but now trying faecal transplantation
What vaccines are there for C. difficile?
Several currently in clinical trials
What are the problems with vaccines for C. difficile?
Problem elderly population to which they are targeted
Impact on impact of the toxin within the gut
Do not reduce colonisation
What control measures should be put in place once someone has been identified to have C. difficile?
Patient should be isolated
Avoid cross-infection of others patients by use of disposables, hand washing (not with alcohol based gels- spores resistant)
Use of chlorine-based disinfection- “deep cleaning”
Overall have cases of hospital acquired infection reduced?
Yes
