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Medical Microbiology > 15. Infection control: bench to bedside > Flashcards

15. Infection control: bench to bedside Flashcards

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1
Q

What are healthcare-associated infections?

A
  1. Infections that are neither present nor incubating when a patient enters the hospital.
  2. It develops during hospital admission or is incubating when a patient leaves the hospital
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2
Q

What impact does healthcare associated infections (HCAI) have on the UK?

A
  1. 4.7% of patients develop HCAIs.
  2. Costs £2.7 billion per year and usually around 1.5% of the NHS budget.
  3. 1.7% of front-line healthcare professionals acquire a HCAI.
  4. around 24,000 deaths per year.
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3
Q

Are HCAI preventable?

A
  1. Around 15-30% are estimated to be preventable.
  2. Need to balance the resources you have with the risk of infection.
  3. We’ve reduced it from 6.4% to 4.7% in the UK.
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4
Q

What is the most common HCAI?

A

Pneumonia

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5
Q

What are the main reasons HCAI occur?

A
  1. Breaches in normal body defences.
  2. Underlying illness that increases vulnerability.
  3. Exposure to microorganisms
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6
Q

What breaches in the body defences can increase the risk of HCAI?

A
  1. Surgery and surgical site infections.
  2. Invasive devices, as any prosthetic material, are magnets for bacteria biofilm formation.
  3. Ventilation as it provides a direct line for the gut flora migrating to the mouth and lungs. and being laid down
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7
Q

How does underlying illness increase the risk of HCAI?

A
  1. They are in hospital because they are not well.
  2. Impaired immune response
  3. Diabetes, cancer
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8
Q

Why does exposure to microorganisms increase in hospital?

A
  1. Lots of ill people in a small space
  2. Patient to patient transmission
  3. Healthcare worker to patient transmission
  4. Environment to patient transmission
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9
Q

What are the main pathogens causing HCAI?

A
  1. MRSA
  2. Clostridium difficile
  3. MSSA
  4. Gram-negative bacilli like Pseudomonas, Enterobacter and Acinetobacter.
  5. Vancomycin resistant enterococci
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10
Q

What are the sources of HCAIs?

A
  1. Endogenous bacteria (the patient’s own bacteria) from their skin or gut flora. E. coli and C. diff
  2. Exogenous bacteria from other patients, healthcare workers, environment and food like MRSA and E. coli
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11
Q

Why is E. coli a very common HCAI?

A

Because it is in everyone’s gut

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12
Q

What are sporadic HCAIs?

A

Single or unrelated cases

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13
Q

What is an outbreak of HCAIs?

A

2 or more related cases

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14
Q

Where do most people acquire C. diff?

A
  1. In hospital
  2. But some come in with it
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15
Q

How quickly did MRSA gain resistance?

A

1940: all Staphylococcus aureus are susceptible to penicillin
1960: 95% of hospital strains are resistant to penicillin
1960: Methicillin and later flucloxacillin are introduced.
1961: 1st MRSA detected
1970s: Increased clinical concern and multi-resistant isolates are reported
1980s: 2 epidemic strains eMRSA 15 and 16 common in UK hospitals
1990s: Excess mortality due to MRSA increasing.

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16
Q

Why could methicillin treat penicillin resistant Staphylococcus aureus?

A
  1. It has a bulky side group.
  2. Which prevents it from fitting in the ß-lactamase active site.
  3. Not as effect as penicillin and bigger doses needed to treat the same infection.
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17
Q

Why was MRSA screening introduced in the UK?

A
  1. It became a big political and healthcare problem.
  2. It was to identify MRSA carriers by screening patients as they come in or before admission.
  3. You can then implement a decolonisation regimen for all these carriers and sterilise rooms.
  4. This reduces the sources of MRSA within healthcare settings and reduces the risk of transmission.
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18
Q

What MRSA screening is now done in the UK?

A
  1. Screening as patients enter high risk areas like ITU.
  2. If the patient has a risk factor.
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19
Q

What does a screening test need to be?

A
  1. Sensitive
  2. Specific
  3. Rapid
  4. Automated
  5. Cost effective
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20
Q

Why do screening tests need to be rapid?

A

Because you need to know about it in time to prevent a problem

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21
Q

Why do screening tests need to be cost effective?

A

You are doing it lots.

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22
Q

How does MRSA screening with PCR work?

A
  1. Uses primers which amplify part of the SCC-mec gene cassette which includes MecA.
  2. Allows direct detection from MRSA from a nasal swab
  3. 91.7% sensitivity and high specific
  4. 1.5 hour processing time
  5. Higher cost than culturing
  6. Cannot do lots of patients at a time.
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23
Q

How is MRSA screening done with Chromagenic agar?

A
  1. Culture based method to grow up staphylococcus aureus.
  2. Contains Flucloxacillin to prevent MSSA growth.
  3. Positive result is pink colony growth
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24
Q

Why was there a big spike in MRSA bacteraemia cases in hospitals?

A
  1. This happens when they introduced mandatory reporting of MRSA bacteraemia.
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25
Q

What cases of MRSA bacteraemia are acceptable in hospitals?

A

Cases where patients were admitted with or because of an MRSA infection.

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26
Q

What MRSA infections are unacceptable in hospital?

A
  1. People catching it from others in hospital
  2. These should be detected and isolated quickly
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27
Q

What measures were introduced to reduce MRSA infections?

A

2002: mandatory reporting introduced
2003: Clean Your Hands Campaign between patients
2003: MRSA/cleaner hospital improvement program
2004: Mandatory target of 50% reduction in MRSA BSI by 2008
2007: Quarterly reporting of MRSA to hospital boards
2007: Change in antibiotic prescribing
2009: MRSA screening for all admission
2014: Admission screening relaxed to high risk groups only

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28
Q

How does C. Difficile colonisation change when people are admitted to hospital?

A
  1. In the gut flora of 0-3% of healthy adults in Europes
  2. 21% colonisation after 1 week in hospital then up to 50% after 4 weeks.
29
Q

What are the reasons C.Diff colonisation increases during hospital admission?

A
  1. Picking it up from other people
  2. Increase in detection as antibiotics kill of the rest of the flora.
30
Q

How does C.Diff survive antibiotic treatment?

A

Spores

31
Q

How is C. Diff spread as a HCAI?

A
  1. Direct Faecal-oral transmission from other patients and from healthcare workers. The bacteria have to be swallowed.
  2. From the environment. The bacteria can survive for 3 hours in the environment.
  3. Spores can survive for months and survive stomach acidity and hypochlorite. So are found on floors, toilets and furniture.
32
Q

What is the epidemiology of C. Diff?

A
  1. Very biased towards the older population.
  2. Almost always after antibiotic treatment.
  3. AND co-morbidity like surgery, renal failure, ITU and cancer
33
Q

What is the range of disease that C. Diff causes?

A
  1. Carrier
  2. Mild antibiotic-associated diarrhoea
  3. Antibiotic-associated colitis causing pain, distension, dehydration and bloody diarrhoea.
  4. Pseudomembranous Colitis which causes significant systemic toxicity.
  5. Toxic megacolon and death.
34
Q

What is Pseudomembranous colitis?

A
  1. A membrane of dead cells and fibres that line the colon.
  2. Stops the gut working properly
  3. This tissue underneath gets damaged by toxins
  4. Can cause Toxic megacolon
35
Q

What is toxic megacolon?

A
  1. An acute form of colonic distension.
  2. Serious condition that requires colon removal or causes death
36
Q

What was contributing to increasing C. diff mortality?

A

A new strain

37
Q

What was C. diff PCR ribotype 027?

A
  1. A epidemic clone of C. diif
  2. Produces around 16-25 times more A and B toxin.
  3. Lots of resistance to antibiotics like fluoroquinolones.
  4. More severe disease
  5. Increased diarrhoea leads to increased environmental contamination facilitating increased transmission.
  6. When patients were on antibiotics this C. diff would thrive.
38
Q

How were C. diff infections managed?

A
  1. Suspecting the cases
  2. Isolating the patient and decontamination
  3. Gloves and aprons must be used
  4. Hand washing using soap
  5. Test the stool for toxin immediately using ELISA.
39
Q

What antibiotic use measures were introduced to reduce C. diff?

A
  1. avoidance of unnecessary antibiotic use
  2. Use of narrowest spectrum antibiotic possible
  3. Use of shortest course antibiotic appropriate
  4. Use of single dose only prophylaxis for surgery
40
Q

How does infection control reduce C. diff infections?

A
  1. Isolation of the patient
  2. Aprons. gloves and hand washing
  3. Hand hygiene
41
Q

Why must hand be washed when dealing with C. diff?

A

alcohol gel is not effective against C. diff spores

42
Q

How did more accurate testing prevent C. diff infections?

A
  1. New, more rapid and sensitive lab tests for C. diff leading to earlier recognition and infection control interventions.
  2. Molecular based techniques
  3. Detection of C. diff gene sequences in stool samples
  4. Real-time PCR detection of genes associated with toxin A and B.
43
Q

What do outbreaks of HCAI indicate?

A

Problems with infection control

44
Q

What do sporadic cases of HCAI indicate?

A

Problems with antibiotic prescribing

45
Q

What does the ribotype of C. diff tell us?

A
  1. What strains are related
  2. Lots of the same ribotype means an outbreak.
46
Q

What are most C. diff HCAI now?

A

Sporadic infections

47
Q

What are most sporadic cases of C. diff provoked by?

A

antibiotic use

48
Q

Why can’t C. diff case numbers go any lower now?

A
  1. Due to the presence of C. diff in the population
  2. The necessity of antibiotic treatment
  3. We have eliminated
49
Q

What is a HCAI outbreak?

A

An HCAI with the same organism affecting 2 or more people thought to have a common exposure to a potential source.

50
Q

What is critical in an HCAI outbreak?

A
  1. Early investigation to enable identification and subsequent elimination of the point source
  2. Laboratory testing to confirm the outbreak the point source and the relatedness of the isolates obtained from the affected patients.
51
Q

What are the steps in investigating an HCAI outbreak?

A
  1. Suspect an outbreak to begin infection prevention and control. This can be hard to suspect.
  2. Verify the diagnosis and construct a working case definition.
  3. find cases systematically and record them.
  4. Perform descriptive epidemiology
  5. Develop hypothesis and evaluate hypotheses epidemiologically
  6. implement infection prevention and control measures
  7. Initiate or maintain Surveillance.
  8. communicate findings
52
Q

What are epidemiological methods?

A
  1. They mostly apply to larger outbreaks.
  2. Construction of an epidemiological curve man shed light on the source of infection
  3. Risk factors of infection can also be demonstrated using cohort or case control studies.
53
Q

Epidemiological curve for point source infections

A
  1. Simple type of outbreak like food poisoning
  2. Curve is simple
  3. Minimum incubation period before 1st case.
  4. All sick around the same time
  5. Doesn’t extend past the maximum incubation period.
  6. Use to help find the point source/common factor
54
Q

Epidemiological curve for point source infections with limited spread

A
  1. first case then minimum incubation period.
  2. Then other cases.
  3. Extends past the maximum incubation period, showing ongoing transmission.
55
Q

Epidemiological curve for continuous source infections

A
  1. Exposure starts then minimum incubation then cases start appearing.
  2. Lots of cases popping up all the time
  3. For example salmonella in a national peanut butter brand.
  4. Usually hard to work out the source
56
Q

Epidemiological curve for point source with an index case and propagated spread

A
  1. index case then incubation.
  2. 1st case and then continuous spread.
  3. Causes an exponential rise in cases until you get immunity.
  4. Like covid or flu
57
Q

What can the epidemiology of an infection tell you?

A

where to look for a potential source

58
Q

What is an antibiogram?

A
  1. A test done on clinical cases of HCAI.
  2. Shows what an infection is resistant to.
  3. different antibiogram = different infection
59
Q

What are phenotypic typing methods of infections?

A
  1. Antibiogram.
  2. Phage typing
  3. Serotyping based on cell wall antigens
  4. Bacteriocin typing based on toxins produced by particular organisms
  5. Multilocus enzyme electrophoresis which is the best and used until recently
60
Q

what is phage typing?

A
  1. Using a set of phages and seeing what the bacteria is sensitive to
  2. Doesn’t work across large location but would in a small hospital.
61
Q

What are genomic typing methods of infections?

A
  1. Restriction fragment length polymorphism
  2. PFGE for MSSA and MRSA
  3. RAPD-PCR for gram negative bacilli
  4. Ribotyping for C. diff
  5. Whole genome sequencing
62
Q

What is restriction fragment length polymorphism?

A
  1. Most important genomic typing method
  2. Chops up the DNA in chunks and look at relative sizes to see if you have the exact same organism
63
Q

What is the problem with using whole genome sequencing?

A

It is new so you need to build up the reference database

64
Q

How can whole genome sequencing give more accurate information about HCAI?

A
  1. Cases of MRSA from a Cambridge hospital
  2. 4 patients in the liver ward all with MRSA infections.
  3. Normally you would say it is an outbreak
  4. Whole genome sequencing showed they were totally unrelated infections.
65
Q

Why is there lots of MRSA in liver wards?

A

Due to high levels of liver damage

66
Q

How was whole genome sequencing used to identify MRSA cases in a baby unit?

A
  1. Closely related cases happen long periods of time apart.
  2. Looks like sporadic cases but going in cycles.
  3. Whole genome sequencing showed they were related and some were genetically identical.
  4. there was transmission from the babies to the parents, the community and the rest of the hospital and back again.
67
Q

How has whole genome sequencing led to new approaches in infection control?

A
  1. Lots of cases were missed with the old method.
  2. If you routinely sequence all pathogens you can see if there has been a transmission event.
  3. Gives you a lot more information and specific strain information
68
Q

How can whole genome sequencing be used in public health?

A
  1. All salmonella cases are sent to the same reference lab
  2. Can look into the source straight away.
  3. Can help find common sources for a variety of public health concerns and infections
69
Q

Why is whole genome sequencing not a useful for vancomycin resistance enterococci?

A
  1. They are common in haematology and ITU patients as they are often exposed to antibiotics.
  2. Most infections are from the same strain and species for WGS is less useful.
  3. 3 or 4 unrelated cases could be seen as an outbreak.

Medical Microbiology (16 decks)

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