Infections Flashcards
What are healthcare-associated infections (HCAIs)?
infections caused by contact with the healthcare environment and personnel
the nature of the setting and the staff can lead to an increased risk of already vulnerable patients acquiring infections
these can be avoided in most cases through appropriate general and/or specific infection control measures
Name the three most common bacterial HCAIs.
Clostridium difficile (C. difficile) methicillin-resistant Staphylococcus aureus (MRSA) Escherichia coli (E. coli)
What are bacteria?
the largest group of microorganisms of medical significance
Name the three main shapes of bacteria.
coccus (circular)
bacillus (rod)
spiral
Name two other shapes of bacteria.
coccobacillus
vibrio (spiral and bacillus)
List the main structural features of bacteria.
flagella fimbriae pili outer capsule cell wall plasma membrane cytoplasm
What is the function of flagella?
thin rigid filament allows movement
What is the function of fimbriae?
hair-like appendage
contributes to the bacteria’s ability to cause disease by binding onto a cell surface
What is the function of pili?
shorter hair-like appendage
help attachment to mucosal cells
involved in bacterial conjugation
What is the function of the outer capsule containing polysaccharides?
to allow the bacteria to bind to cell surfaces
to evade phagocytosis
What is the function of the plasma membrane?
phospholipid bilayer
partially permeable
allows transportation of substances into and out of the cell
What is the function of the cell wall?
complex semi-rigid structure
enables bacteria to be classified into gram-positive or gram-negative
What are the differences in cell wall composition between gram-positive and gram-negative bacteria?
gram-positive has a thicker peptidoglycan layer than gram-negative
gram-negative has an extra plasma membrane above the thin peptidoglycan layer
gram-positive has a lipoteichoic acid, gram-negative has lipoproteins and lipid A (toxin)
How can you distinguish between gram-positive and gram-negative bacteria?
when dyed, the different colour of the bacteria is due to a different cell wall composition
gram-positive stain crystal violet
gram-negative stain pinkish-red
What does the cytoplasm in bacteria contain?
water, enzymes, ribosomes, circular DNA, plasmids
What are viruses?
the smallest type of infectious particle
10-300nm in diameter (average 100)
List the main structural features of viruses.
capsid
envelope (not always present)
virulence factors
What is the function of the capsid?
made of capsomere proteins
contains the genetic material of the virus - ssRNA, dsRNA, ssDNA, OR dsDNA
viruses can also contain partial strands
Name the two types of shape that the capsid can form.
icosahedral
helical
What is the function of the viral envelope?
carries the capsid of genetic material
composed of a lipid bilayer which helps the virus attach to the host cell and release the genetic material inside the cell
What is the function of virulence factors?
receptors allow the virus to target certain cell types
Name some examples of types of viruses.
bacteriophage - infects bacteria
herpesvirus
picornavirus
Viruses are classified into groups/families based on which characteristics?
type of nucleic acid (DNA or RNA)
shape
structure
method of replication
How do viruses infect specific living cells?
based on the presence of suitable receptors
HIV only infects T-helper cells because the HIV virulence factors have a complementary shape to that of the T-helper CD4 receptor
Where do all viruses replicate?
inside another living cell
How does a bacteriophage replicate?
bacteriophage binds to cell
releases phage (virus) DNA
the viral infection then enters the lytic or lysogenic cycle
What happens in the lytic cycle?
phage DNA takes over the cell machinery
the cell starts to synthesise new phage DNA and proteins to create new bacteriophages
the synthesis and accumulation of new bacteriophages cause the bacteria to lyse
bacteriophages are released out and can then infect other bacteria
What happens in the lysogenic cycle?
bacteriophage binds to cell
releases phage (virus) DNA
phage DNA incorporates into the bacterial chromosome which creates a prophage (provirus)
the viral infection is latent and will cause no damage
when the bacteria divide, the phage DNA is also copied
the prophage may eventually excise from the bacterial chromosome and enter the lytic cycle
What is specialised transduction?
the lysogenic cycle gives rise to this pathway
bacterial chromosomes are transferred with the phage DNA to other bacteria through conjugation
Name the six stages of infection.
infectious agent reservoir portal of exit mode of transmission portal of entry susceptible host
What is the ‘infectious agent’?
e.g. bacterium, virus, parasite, fungus
What is the ‘reservoir’?
the place where the microorganism resides, thrives and reproduces
e.g. food, water, environmental surfaces, humans, animals
What is the ‘portal of exit’?
the way the microorganism leaves the reservoir
What is the ‘mode of transmission’?
how a microorganism transfers from one carrier to another by direct or indirect transmission
What is the ‘portal of entry’?
the entry point where the microorganism enters the host’s body
e.g. cuts in the skin, open wounds, tubes such as urinary catheters
What is the ‘susceptible host’?
the person who is at risk of developing an infection
e.g. age, underlying chronic disease, certain medication, invasive devices, malnutrition
How can you break the chain of infection at the ‘infectious agent’ stage of transmission?
improve knowledge about gram-negative bacteria
How can you break the chain of infection at the ‘reservoir’ stage of transmission?
understand reservoir (GI tract, food, environmental)
How can you break the chain of infection at the ‘portal of exit’ stage of transmission?
hand hygiene, aseptic technique, safe handling of body fluids, environmental cleaning
How can you break the chain of infection at the ‘mode of transmission’ stage?
decontamination of instruments and equipment, environmental cleaning, isolation of patients with transmissible infections, safe handling of linen
How can you break the chain of infection at the ‘portal of entry’ stage of transmission?
delivery of safe practices at every patient intervention for device and procedures
How can you break the chain of infection at the ‘susceptible host’ stage of transmission?
perform and act on risk assessment
ensure good patient hydration and nutrition
What is pneumonia?
a form of acute respiratory infection that affects the lungs
caused by bacteria, viruses or fungi
accounts for 22.8% of respiratory infections
What are the most common causes of pneumonia?
Streptococcus pneumoniae
Haemophilus influenzae type b (Hib)
the respiratory syncytial virus
Pneumocystis jiroveci
What is Streptococcus pneumoniae?
the most common cause of bacterial pneumonia in children
What is Haemophilus influenzae type b (Hib)
the second most common cause of bacterial pneumonia
What is the respiratory syncytial virus?
the most common viral cause of pneumonia
What is Pneumocystis jiroveci?
one of the most common causes of pneumonia in infants infected with HIV
accounts for at least 25% of all pneumonia-related deaths in HIV-infected infants
What are the common characteristics of the lung in a patient with pneumonia?
alveoli with fluid
inflammation of lung tissue
blockage of the bronchiole
List some of the main causes of urinary tract infections (UTIs).
catheter in situ that has bypassed the body’s defences
medication (e.g. antibiotics) that decrease the body’s ability to fight infection
Urinary tract infections can be divided into which two categories?
upper tract and lower tract
What are the two types of upper tract infection?
pyelonephritis (kidney infection)
ureteritis (ureter infection)
What are the two types of lower tract infection?
cystitis (bladder infection)
urethritis (urethra infection)
What is the most common cause of upper tract infection?
Proteus
due to the presence of bladder or kidney stones
What is the most common cause of lower tract infection?
E. coli
What is the risk of acquiring a surgical site infection (SSI) following replacement surgery?
hip replacement 0.4% in 2018/19
knee replacement 0.4% 2018/19
What is the risk of acquiring an SSI following a long bone fracture
inpatient/readmission 1.0% in 2018/19
repair of neck of femur 0.9% in 2018/19
What is the risk of acquiring an SSI following GI surgery?
large bowel surgery 9.0% in 2018/19
small bowel surgery 5.6% in 2018/19
What is the risk of acquiring an SSI following cardiac surgery?
coronary artery bypass graft (CABG) 2.3% in 2018/19 this included infections at vein harvesting sites and the sternum
What is the risk of acquiring an SSI following vascular surgery?
3.3% in 2018/19
What is the risk of acquiring an SSI following spinal surgery?
1.5% in 2018/2019
What is the risk of acquiring an SSI following breast surgery?
0.8% in 2018/19
What is the risk of acquiring an SSI following cranial surgery?
1.3% in 2018/19
What is the most common cause of SSIs?
Enterobacterales 30.0% in 2018/19
What are the three most prevalent species that make up the Enterobacterales?
E. coli (30.2%)
coliforms (19.6%)
Proteus mirabilis (13.3%)
Which other bacterium is a common cause of SSIs?
Staphylococcus aureus (22.1%) the methicillin-resistant S. aureus (MRSA) and methicillin-sensitive form increased by 1.0% from 2017/18 to 2018/19
What is Streptococcus pneumoniae?
gram-positive spherical bacteria
alpha-haemolytic (under aerobic conditions)
beta-haemolytic (under anaerobic conditions)
How does Streptococcus pneumoniae gain entry into a person?
spreads by direct person-to-person contact via respiratory droplets and by autoinoculation in people carrying the bacteria in their upper respiratory tracts