CSI 3 HAI Flashcards
What is Hospital Associated/Acquired Infections
An infection that patients get while receiving treatment for medical or surgical conditions
Can HAI be prevented
Yes, many are preventable
Problems with HAI
A significant source of complications across the continuum of care
Can be transmitted between different healthcare facilities
How many % of patients in England get HAI
6.4%
What is normally associated with HAI
Procedures like surgery
Devices used in medical procedures such as catheters and ventilators
Anything that exposes the inside to the outside
Source of micro-organisms
Can be caused by micro-organisms already present in the patient’s own body.
Opportunistic Infection by opportunistic bacteria due to weakened immune system or breached by surgery or other medical procedures
Locations that could have HAI
Can occur at ALL types of healthcare settings:
1) Acute care hospitals
2) Ambulatory surgical centres
3) Dialysis facilities
4) Outpatient care
5) Long term care facilities
Why is HAI more problematic in outpatient settings?
Outpatient settings often have limited capacity for infection control compared to acute care settings
Eg. Ambulatory surgical centres vs Hospitals
Other issues HAI can cause in outpatient settings
HAI patients often move between healthcare facilities to get better treatment
Co-ordinated prevention efforts must expand across the continuum of care so resistant infections will not spread to others
Central Line Associated Bloodstream Infections (CLABSI)
A serious HAI that occurs when germs enter the bloodstream through the central line (tube in the large vein that empties the heart)
Methicillin Resistant Staphylococcus aureus
A type of bacteria resistant to many commonly used antibiotics (including methicillin)
Causes life threatening bloodstream infections, pneumonia, and surgical site infections
Importance of prevention practices
Implementing existing prevention practices can have up to 70% reduction in certain HAIs.
Reduce resistant bacteria through coordinated activities between healthcare facilities in a given area
Other measures to prevent HAIs
Proper education and training (infection control, hand hygiene, attention to safety, Antibiotic stewardship)
Careful insertion, maintenance and prompt removal of catheters
Antibiotic Stewardship
the effort to measure and improve how antibiotics are prescribed by clinicians and used by patients
Further strategies for HAIs
Expand implementation of strategies known to prevent HAIs
Advance development of effective prevention tools
Explore new prevention approaches
5 common types of HAIs
- Catheter Associated HAI
- Surgical site infections
- Bloodstream infections
- Pneumonia
- Clostridium difficile
4 risk factors of HAIs
- Medical procedures and antibiotics use
- Organisational factors
- Patient characteristics
- Behaviour of healthcare providers and their interactions with the healthcare system
Transmission of infectious diseases
Results from interaction of an AGENT, HOST and ENVIRONMENT
Chain of infection
INFECTIOUS AGENT -> RESERVOIR -> PORTAL OF EXIT -> MODE OF TRANSMISSION -> PORTAL OF ENTRY -> SUSCEPTIBLE HOST
Transmission occurs when the Agent leaves its RESERVOIR (eg. host) through a PORTAL OF EXIT and is conveyed by some MODE OF TRANSMISSION and enters through an appropriate PORTAL OF ENTRY to infect a SUSCEPTIBLE HOST
Reservoir
The habitat in which the infectious agent normally lives, grows and multiplies.
- includes humans, animals and the environment
- may or may not be the source from which the agent is transferred to a host
e. g. the reservoir could be soil but the source may be improperly canned food.
Examples in hospitals
- healthcare staff
- medical equipment
- patients that are carriers
Human reservoirs
When diseases are transmitted from person to person WITHOUT INTERMEDIATES –
- STDs, measles, mumps, streptococcal infections.
- They may or may not show signs of illness. Diseases can be eradicated when humans are the only reservoirs for a disease. It is eradicated after the last human case is identified and isolated
eg. smallpox
Carrier
A person with inapparent infection who is capable of transmitting the pathogen
Asymptomatic/ healthy/ Passive carrier
A person who never experiences any symptoms despite being infected
Incubatory carrier
Person that can transmit the agent during the incubation period before the clinical illness begins
Convalescent carrier
Person that has recovered from their illness but remains capable of transmitting it to others
Chronic carrier
Harbours a pathogen
Eg. HepB for months or years after infection
Carriers are dangerous because they often transmit diseases
- might not realise they are infected so take no precautions to prevent transmission
Animal reservoirs
Pathogens in animals, many of which are transmitted from animal to animal with human as incidental hosts
Zoonosis
An infectious disease that is transmissible under natural conditions from vertebrae animals to humans
- anthrax (sheep) and plague (rodents)
- some new human disease are thought to have emerged from animal hosts (eg. HIV/AIDS, Ebola, Covid-19?)
Environmental reservoirs
Plants, soil, water
Many Fungal agent live and multiply in soil
Portal of exit
Path by which pathogen leaves it host
- usually corresponds to the site where the pathogen is localised (eg. influenza and mycobacterium tuberculosis exit the respiratory tract)
Body fluids, coughs, sneezing
Direct transmission
When the infectious agent is transferred from a reservoir to a susceptible host by:
- direct contact: skin to skin contact, kissing, intercourse. Also refers to contact with soil or vegetation harbouring infectious organisms.
- droplet spread: spray with relatively large, short range aerosols produced
by sneezing, coughing or talking. Droplet spread transmission is by direct
Indirect transmission
Transfer of an infectious agent from a reservoir to host by:
- suspended air particles
- inanimate objects (vehicles)
- animate intermediates (vectors)
Airborne indirect transmission
Infectious agent carried by DUST or DROPLET NUCLEI suspended in air
- includes material that has seeded on surface and become resuspended by air currents and infectious particles blown from the soil by wind
- droplet nuclei are dried resides less than 5 microns in size
- in contrast to droplets that fall to the ground within a few feet droplet
nuclei may remain suspended in the air for long periods of time and are
blown over long distances e.g. measles virus
Vehicle borne indirect transmission
Vehicles such as
- Food
- Water
- Air
- Blood
- Fomites
A vehicle may positively carry a pathogen or provide an environment in which the agent grow, multiplies or produces toxins
Vector borne indirect transmission
Mechanical transmission
Biological transmission
Vector borne indirect transmission - Mechanical transmission
Facilitated by a mechanical vector, an animal that carries a pathogen from one host to another without being infected itself
Vector borne indirect transmission - Biological transmission
- occurs when pathogen reproduces within a biological vector that transmit pathogen from one host to another
Arthropods are the main vectors responsible
Eg. mosquitoes, fleas or ticks - the causative agent e.g. malaria undergoes maturation in an intermediate
before it can be transmitted to humans.
Examples of modes of transmission in hospitals:
- patient to patient or doctor to patient contact
- staff/visitors not washing hands
- shared equipment
Portal of entry
Manner in which pathogen enters a susceptible host:
- must provide access to tissues in which a pathogen can multiply or a toxin can act
- often the same portal as portal of exit Eg. mucous membranes and blood
Examples in hospitals:
- open wounds
- catheters
- cannulas
- vomit
- diarrhoea
- respiratory
Host susceptibility
Depends on:
1. Genetic or constitutional factors - may increase or decrease susceptibility Eg. sickle cell and malaria
- Specific immunity
- Non-specific factors that affect an individual’s ability to resist infection or to limit pathogenicity
Specific immunity
Refers to protective antibodies directed against a specific agent.
Antibodies may be acquired through:
1. Response to infection, vaccine, or toxoid (toxin is deactivated but still stimulates antibody production)
- Transplacental transfer from mother to foetus
- Infection of antitoxin or immune globulin
Non-specific Factors
- Skin
- Mucous Membrane
- Gastric Acidity
- Cilia in the respiratory tract
- Cough reflex
- Non-specific immune response
Non-specific factors that may increase susceptibility by disrupting the host defences
- Malnutrition
- Alcoholism
- Disease
- Therapy affecting the non-specific immune response (Innate Immunity)
Control measures
Directed against section infection chain that is most susceptible to intervention.
Knowledge of portal of entry and exit and modes of transmission help determine appropriate control measures
Processes in the chain of infection that interventions target
- Controlling or eliminating agent at the source of transmission
- Intervening with the mode of transmission
- Protecting portals of entry
- Increasing host’s defences
- Controlling or eliminating the agent at the source of transmission
- Give antibiotics to ill patient to eliminate infection
- Asymptomatic infected patient treated to clear infection and reduce risk of transmission
- soil decontaminated or covered to prevent escape of agent
- Intervening with mode of transmission
- Direct transmission: Isolating someone with an infection or counselling people to avoid the specific type of contact associated with transmission
- Vehicle borne transmission: eliminate decontaminate vehicle
- Decal-oral transmission: rearrange environment to reduce risk and try to change behaviour eg. promoting washing hands
- Airborne: Modify ventilation / air pressure and filter/treat the air
- Vector borne: focus on controlling vector population
- Protecting portals of entry
- Bed nets to prevent malarial mosquitoes
- mask/gloves to protect from blood/droplets
- long pants/sleeves, insect repellant to reduce risk (eg. Lyme disease which is transmitted by tick bites)
- Increasing host defences
- Vaccination to promote development of specific antibodies
- Prophylactic use of antimalarial drugs prevents infection from taking root
Preventing a pathogen from encountering a susceptible host
Herd Immunity.
A degree of herd immunity is needed to prevent/interrupt an outbreak which varies by disease
In practice, immunisation levels as high as 85-90% has not prevent measles/rubellea outbreaks
Issue is that the few susceptible people are often clustered in sub-groups defined by socioeconomic or cultural factors. If the pathogen introduced into these sub-groups, an outbreak may occur
Herd Immunity
If a high enough proportion of individuals in a population are resistant to an agent then those few who are susceptible will be protected by the resistant majority since the pathogen is unlikely to find those few susceptible individuals
5 moment os hand hygiene
- Before touching a patient
- Before a clean/aseptic procedure
- After body fluid exposure risk
- After touching a patient
- After touching patient surroundings
Gram Positive Bacteria
Stains purple after Gram staining
Cell walls composed mostly of peptidoglycan or murein
Eg. Staphylococcus aureus, Streptococcus pneumonia, Clostridium dificile, Enterococcus spp, Mycobacterium tuberculosis
Gram Negative Bacteria
Stains red or pink after Gram staining due to counter stain safranin
Cell walls with only a thin layer of peptidoglycan and an outer membrane with lipopolysaccharide component not found in Gram positive bacteria
Eg. Escherichia coli, Neisseria gonorrhoeae, Pseudomonas aeruginosa, Salmonella spp, Acinetobacter baumannii
Infection test results
High C-Reactive Protein (CRP) level = indicative of infection/inflammation
High WBC count = indicative of infection
Normal oxygen saturation level = 95-100%
Could dip during infections
- Whether patients are on air and how much, etc, are required to judge from oxygen saturation
Higher Respiratory Rates
(normal = 12-20, higher for children)
Sequence of septic shock
- Hypotension (low blood pressure)
- Tachycardia (high heart rate)
- Tachypnoe (high respiratory rate)
Sepsis
The body’s extreme reaction to an infection
Shock
An imbalance in supply and demand
Oral vs intravenous antibiotics
Intravenous antibiotics have faster delivery and have a systemic effect making it better for the treatment of sepsis
Oral antibiotics is slower
CSU (catheter specimen urine) - Microscopy Culture sensitivity
- Positive for epithelial cells
- High number of organisms and white blood cells
4 mechanisms of antibiotic resistance
- Altered target site - change in structure of the site antibiotic inhibits
- Inactivation of the antibiotic
- Altered metabolism profile
- Decreased drug accumulation
- Altered target site antibiotic resistance
Arise via acquisition of alternative gene or a gene that encodes a target-modifying enzyme.
Penicillin and Methicillin mechanism
Beta-lactams work by binding to penicillin binding to penicillin binding proteins which are needed for peptidoglycan synthesis
Streptococcus pneumonia mechanism to resist Erythromycin
Acquires erm gene
This gene encodes an enzyme that methylates antibiotic target site in the 50S ribosomal subunit
MRSA mechanism
MRSA encodes a alternative penicillin binding protein (PBP2a)
Alternative PBP2a has low affinity for Beta-lactams = MRSA can make cell wall in presence of B-lactam antibiotics
Erythromycin mechanism
Inhibits translation by binding to ribosomes
Methylation of the target site means that erythromycin cannot bind
- Inactivation of antibiotic
Enzymatic degradation or alteration rendering antibiotic ineffective
Inactivation can also br enzyme independent
Beta-lactamase and chloramphenicol acetyltransferase
ESBL and NDM-1 are examples of broad spectrum beta-lactamase which can degrade a wide range of B-lactams as they break down the B-lactam ring
Klebsiella pneumonia bacteria produce enzymes call carbapenemases which breakdown carbapenem drugs (types of B-lactam)
- Altered metabolism profile
Increased production of enzyme substrate can out compete antibiotic inhibitor
Eg. Increased production of p-aminobenzoic acid PABA confers resistance to sulphonamides
Alternatively, bacteria switch to other metabolic pathways reducing requirements for PABA
Eg. Sulphonamides like Protonsil targets folate biosynthesis. Bacteria overcome this by getting folate from the environment or massively increasing number of enzyme synthesising folate so that drug dosage is insufficient
- Decreased drug accumulation - pump out antibiotic
Reduced penetration of antibiotic into bacterial cell wall and/ or increased efflux of antibiotics out of the cell means the drug does not reach the concentration required to be effective
Selectively pumps out by recognising and ejecting toxic chemicals
Eg. Pseudomonas aerunginosa can pump out several antibiotic drugs including:
- fluoroquinolone
- beta-lactams
- chloramphenicol
- trimethoprim
Restricting access of antibiotic
By changing entryways or limiting number of entryways
Eg. Gram negative bacteria have an outer-membrane that protects them from their environment
This membrane can selectively keep antibiotics from entering
Causes of antibiotic resistance
Excessive use; exposure to selection pressure drives natural selection and influx of newer resistant bacteria
Not finishing an antibiotics course; many bacteria, including slightly resistant ones, remain
Antibiotic Stewardship
strategy
Shorten antibiotic therapy to the minimum effective duration
Goal is to maximise benefit to patient by curing disease while minimizing risks of antibiotic resistance and side effects from antibiotics
Beta-lactam antibiotics
Contain a Beta-lactam ring
Works by inhibiting cell wall biosynthesis
Interferes with synthesis of peptidoglycan component of bacterial cell wall by mimicking components of cell wall
Enzymes in bacteria confuse B-lactam antibiotics for cell wall precursors and bind to it.
Deactivates the enzyme hence bacterial growth stopped
Beta-lactamase
Enzymes produced by bacteria to provide resistance to B-lactams antibiotics
B-lactamase inhibitors
Inhibit activity of B-lactamase, allowing B-lactams antibiotics to work properly
Co-amoxiclav
Antibiotic containing amoxicillin and clavulanic acid.
Amoxicillin is B-lactam antibiotic
Clavulanic acid is B-lactamase inhibitor
What led to Mr. Rachett’s C.difficile infection
- Admitted for elective hip replacement
- Developed post-operative urine retention
- Catherised, likely transmission of gut commensals
- Developed E.coli urinary sepsis (E.coli can sit on skin)
- Treated with broad spectrum co-amoxiclav
- Disruption / killing of gut microbiome
- Activation of toxinogenic C.difficile
What is the duty of candour
Doctors must be open and honest
Own up to mistakes when things go wrong
Must apologise, write out all in notes, explain to patient and take responsibilty
Why are antibiotics important
Medical advances are dependent on our ability to fight infections using antibiotics
Surgeries (joint replacements, organ transplants, cancer therapy)
Treatment of chronic illness ( diabetes, asthma, dialysis, rheumatoid arthritis and cancer)
Why is antibiotic resistance a problem
One health problem and can spread between people, animals and the environment
Why does antibiotic resistance occur
Antibiotics provide a selective pressure for natural selection.
Antibiotics kill the bacteria causing the illness, as well as the good bacteria protecting the body. Drug resistant bacteria then take over and some can give their resistance to other bacteria.
How can other germs become antibiotic resistant quickly
Resistance gene often found in plasmids which means some bacteria can share their DNA and make others resistant
How does resistance pass between bacteria
Resistance traits can be inherited from generation to generation
Pass directly from germ to germ by way of mobile genetic elements (MGE)
Plasmids (MGE)
extra-chromosomal circular DNA which often carry multiple resistance genes. Selection for one maintains resistance to all so a single antibiotic can select for multi-drug resistance if it is encoded in the plasmid. There is an energy cost to helping a plasmid so there needs to be a real selection pressure. They can be swapped between bacteria.
Transposons (MGE)
molecular shuttles that integrate plasmids into chromosomal DNA. Allows transfer of genes from plasmid to chromosome and vice versa to enable transmission.
Naked DNA (MGE)
DNA from dead bacteria is released into the environment so bacteria in close
proximity can scavenge the free-floating DNA to incorporate into their own DNA.
Bacteriophages (MGE)
viruses that attack bacteria and can carry DNA from germ to germ.
Transduction
Resistance genes can be transferred from one germ to another via bacteriophages.
Conjugation
Resistance genes can be transferred between germs when they connect via a pilus.
Transformation
Extracellular resistance genes released from nearby live or dead germs can be picked up directly by another germ.
