Bloodstream Infections Flashcards
1
Q
Why should blood normally be sterile?
A
Lysozyme
Leucocytes
Immunoglobuline (sIgA)
Complement
2
Q
What is a transient bloodstream infection?
A
This is wherby bacteria can enter the bloodsteam but only for a few minutes
They are quickly moped up by the leucocytes etc
3
Q
What causes a transient blood infection to become a bloodstream infection?
A
If host defences are overwhelmed or evaded
4
Q
What is the mortality associated with bloodstream infections?
A
Between 10 and 40%
5
Q
Other than the high mortality rate associated with BSI, what is the main major concern with BSI?
A
Patients who survive sepsis have a x2 times risk of dying in the next 5 years
Patiens usually suffer physical and cognitive impairment after survival
6
Q
What is the mortality of BSI based on?
A
It is based on what organism you are infected with vs host immune system
7
Q
What are the four ways that a bloodstream infection can occur, give examples of each?
A
A focal point of infection within the body outside of the blood (most common) -> e.g. a UTI (urosepsis) or S. pneumonia pneumonia spread to blood
Normal flora of the skin/mucous membrane such as S. aureus enter through cuts or wounds/burns etc
Gut flora enter through GIT perforation, infection or diverticulitis e.g. E. Coli
Direct introduction e.g. IV drug users, intravenous catheters or contaminated medical equipment
8
Q
What are the different names for BSIs, what do they mean, what one should you use?
A
Bacteraemia - just means bacteria present in the blood
Septicaemia - focuses on clinical symptoms
BSI should be used
9
Q
What are the different names for BSIs, what do they mean, what one should you use?
A
Bacteraemia - just means bacteria present in the blood
Septicaemia - focuses on clinical symptoms
BSI should be used
10
Q
What are the four steps to a bloodstream infection?
A
Systemic Inflammatory Response Syndrome (SIRS)
Sepsis
Sever Sepsis
Septic Shock
11
Q
What is SIRS?
A
Systemic Inflammatory Response Syndrome
The initiation of clinical symptoms due to immune response to toxic bacteria or to their products
12
Q
What is sepsis?
A
This is where there is clinical evidence of infection along with a systemic response
Two of the following:
- Fever
- Tachycardia
- Tachypnoea
- White cell count >12,000
13
Q
What is sever sepsis?
A
Sepsis plus evidence of abnormal perfusion of any organ, indicating more sever organ dysfunction
i.e. sepsis + spread to one other organ
This is where we see te 5 year mortality
14
Q
What is septic shock?
A
This is where patients with septic syndrome develop hypotension
This represents a critical stage that requires immediate intervention or the patient will die
This is one of the biggest hospital emergencies
15
Q
What causes septic shock, what organisms, how does it happen?
A
It is most frequently seen with gram negative BSIs but less commonly can be seen in gram-positives
Gram negatives:
- Lipid A portion of endotoxin triggers a series of reactions including production of TNF, IL-1 and complement which contribute to shock response
Gram positives:
- Associated with pneumococal infections (GAS) or staphylococcal BSIs
16
Q
What are the three types of BSIs?
A
Transient Bloodstream Infections
Intermittent Bloodstream infections
Continuous Bloodstream Infections
17
Q
Define a transient bloodstream infection, when would you see it
A
The temporary presence of bacteria in the bloodstream lasting less than 20 minutes
Self limiting - may not cause symptoms
Often seen after dental work e.g. S. viridans, localised infections such as pneumococcal pneumonia, dental extraction or chewin with poor dental hygiene, or intravenous drug abuse
18
Q
Define an intermittent BSI
A
Bacteria present in the bloodstream at irregular intervals
Lasts for hours or longer, occuring at specific times
Symptoms may recur with each episode of bacteraemia
E.g. undrained intra-abdominal abscesses, earlly in the course of a variety of systemic and localised infections such as pneumococcal pneumonia
19
Q
Define continuous BSI, give some examples
A
The persistant presence of bacteria in the bloodstream, suggesting a severe infection that has overwhelmed host defences
Its ongoing and wont go away without treatment
Symptoms are persistant and can lead to sever illness
Infections related to catheters, S. aureus, HIV or cancer showing ongoing bacteraemia
20
Q
What are the four most common infections that cause sepsis in adults?
A
36% of patients had a lung infection
25% had a UTI
11% had a gut infection
11% had a skin infection
21
Q
What sepsis is associated with oropharynx carriage?
A
N. meningitidis colonises the oropharynx
This can spread to blood = sepsis
This can then invade meninges to cause meningitis
22
Q
What sepsis is associated with oral carriage?
A
Dentistry manipulation of teeth can lead to oral streptococci entering the blood
Occult bacteraemia -> can set up infection in damaged heart valves
results in endocarditis
23
Q
What sepsis is associated with long-term central line catheters?
A
Coagulase-negative staphylococci
These can form biofilms and give rise to a continuous bacteraemia
-> line needs to be removed
24
Q
What sepsis can be associated with bacterial pneumonia?
A
S. pnemonia caused pneumonia
Results in a transient bacteraemia
25
What sepsis is associated with cellulitis
Staphylococcus aureus
26
What sepsis is associated with liver abscesses
Liver abscesses tend to be polymicrobial -> usually sourced from appendix
Can cause a 'dirty' poymicrobial bacteraeia -> coliforms and such
27
What sepsis is associated with pyelonephritis
Urosepsis
E. Coli
Can cause septic shock (think Gram neg)
28
What kind of sepsis is associated with necrotisin fasciitis?
Group A streptococcus
29
What are the six most common causes of community acquired BSI in the immuno-cometent?
E. Coli (UTIs)
S. pneumoniae (pneumoniae)
S. aures (skin infections)
Enterobacteriaeceae
Neisseria (nasal colonisation)
B-haemalytic strep (S. pyogenes)
30
What are the nine most common causes of healtchare acquired BSIs in the immuno-competent
E. Coli (UTIs)
S. aureus (skin infections)
Enterobaceraceae -> Klebsiella
CNS -> biofilms/catheters etc
P. aeruginosa -> same as meningitis -> Beaumont etc
Enterococcus
Anaerobes -> Clostridiodes
S. pneumo -> pneumonia
Yeast -> candida/aspergillus
31
What are the some BSI pathogens associated with the immuno-compromised
Same organisms as in immuno-competent +
- L. monocytogenes (elderly)
- Corynebacterium sp
- Candida species + other fungi
- Mycobacterium
32
What are the some BSI pathogens associated with the immuno-compromised
Same organisms as in immuno-competent +
- L. monocytogenes (elderly)
- Corynebacterium sp
- Candida species + other fungi
- Mycobacterium
33
What is the most common ddrug/treatment associated with BSIs?
Chemo -> constant bacteramiae seen
34
What is a communinty associateddd BSI?
A BSI which occurs in an individual who was previously healthy
They are typically linked to focal infections:
- urinary tract infections - urosepsis
- pneumococal pneumonia - spread from lung
- skin and soft tissue infetion - staph
35
What is one of the reasons why S. aureus BSIs are so common?
S. aureus focal point might not be evident
S. aureus can cause osteomyelitis -> skin infection -> spread to bone, this infection might not be detectable i.e. might be treated and thought cleared -> metastatic spread from bone to blood etc etc
36
What are the relative frequencies of each causative organism of CA BSI in adults?
E. Coli = 25% -> NB, most common in Mater
S. pneumo = 22%
S. viridans = 10%
S. aureus = 10%
Others (Haemophilus, Neisseria, GNBs etc) = 17%
37
What are the four most common CA BSIs in children
S. pneumo (pneumonia)
N. meningitidis (carriage?)
S. aureus ( skin infections)
E. Coli
38
What has been the most significant change in CA BSI in children over the last few years?
Since the introduction of the Hib vaccine, H. influenza associated BSIs have decreased significantly
39
What are some reasons for the increase in HA BSIs, give an example of a scenario explaining this?
Increase in invasive procedures
Prolonged hospital stays
Foreign bodies such as catheters/central lines etc
e.g. a healthy pregnant woman comes into hospital for a C section (invasive procedure), she will now stay 5 days recovery in hosp (prolonged stay), a catheter will be put in (foregin body) -> patient now at very high risk of BSI
40
What are five invasive procedures with the highest risk of BSI?
Endoscopy: 0-20%
- CoNS, streptococci, diptheroids
- ?perforates bowel
Colonoscopy: 0-20%
- E. coli, Bacteroides species
- ? perforates bowel
Barium enema: 0-20%
= Enterococci, aerobes + anaerobic GNBs
- ? perforates bowel
Dental extraction: 40-100%
- transient BSI
- GBS = S. viridans
Prostate Transurethral resection: 0-40%
- Coliforms, enterococci, s. aureus
-
41
Comment on the rates of HCA BSI in ireland
2012 = 13%
2017 = 10%
2023 = 10.4%
*HCA BSI increasing slightly over last 5 years
42
What is the breakdown of the causes of BSIs in Ireland, origins of BSIs?
31/64 = Primary infections due to catheters
33/64 = Secondary infections due to focal infections:
- 33% = UTIs
- 24% = DIG
- 12% = Skin/Soft TI
- 12% = Surgical site infections
- 9% = pulmonary infection
- 9% = oher infections
43
Why are CNS BSIs often difficult to diagnose?
CNS are commensals of the skin
=> hard to determine if a CNS is a true infecion or just a commensal contaminant => hence why we take 3 sets of BCBs
44
How are E. Coli, S. aureus, S. pneumo, Enterococci, GNBs HCA BSIs trending?
E. Coli trending upwards
S. aureus flatlining
S. pneumo was high prior to covid, drop during covid, rising again
Both Ent faecium and Faecalis were rising, faecium much higher than faecalis, faecium seems to have peaked
Klebsiella increasing, P. aeruginosa flatlines and acinetobacter steadily low numbers
45
Comment on E. Coli trends and relative resistant strains
(3)
Invasive E.Coli decreased by 7.7% from 2019 to 2023
Proportion of ESBL+ decreased from 11.3% to 8.7%
=> proportion of ESBL decreasing
Very few CPEs -> stable at 3-4 cases a year
46
Comment on S. aureus trends and relative resistance
(3)
S. aureus has increased by 9.2% from 2019-2023
MRSA has decreased to 9.7% -> lowest to date
MSSA BSIs are increasing though
47
Comment on K. pneumoniae trends and relative resistance
K. pneumonia decreased by 10% between 2019 and 2023
Slight decrease in ESBLs, quinolone resistance and MDRKP
Number and proportion of Carbapenem-resistant is stable -> overall low in Ireland but needs to be monitored
48
Comment on E. faecium trends and resistance
Since 2012 the proportion of VREfm BSI has been over 40% -> we used to be 3rd worst in Ireland
VRE BSI have decreased from a peak of 46% in 2015 down to 21.4% in 2023 -> massive decrease -> still above European average but way down
49
Comment on P. aeruginosa trends and resistance
P. aer BSI have been stable between 2019 and 2023
MDR have decreased from 6.4% in 2019 to 4.8% in 2023
Pseudo high before covid, droped, high again but lower than pre-covid
50
Comment on S. pneumo trends and resistance
Pre-pandemic high of 360 cases, drop to 179 in covid years, increase again
Number of penicillin resistant non wild type strains has decreased
51
Comment on Acinetobacter trends and resistance
There was no MDR Acinetobacter resistance detected in 2023 in Ireland
Major problem in Southern and Eastern Europe
- some countried reporting relative resistance of 75% or more
- what happens in southern Europe tends to happen to us
52
Comment on GAS trends
Between October 2022 and August 2023 there was an unusual and unreasonal upsurge in GAS disease, the majority of which in children (<18)
An established relationship between Varicella infection and subsequent GAS i.e. children who got chickenpox subsequently got GAS
53
What are the most common BSIs in newborns?
Group B streptococci (from mothers flora)
E. Coli
CNS
Candida
54
What are some issues with getting BSI samples for neonatal BSIs?
Specimen collection is so difficult
Small blood volume only
Contamination - samples nearly always contaminated
55
Why has the spectrum of organisms we detect in immuno-compromised BSI changed over the years?
Lengthening periods of neutropenia and duration of hospital stay
Increased use of CVC
Increased use of broad-sepctrum antibiots -> chronically ill immuncompromised e.g chemo patients on long term broad spectrum
Were seeing a high incidence of infection with organisms that are gnerally non-virulent in the normal host and form part of the normal flora e.g. CNS, enterococci, candida etc etc
56
What are five requirements of a good blood culture?
Utilise culture medium suitable for the recovery of small numbers of all potential pathogens including fastidious
Neutralise or remove antimicrobial substances e.g. resin/charcoal
Minimise risk of contamination
Facilitate earliest possible detection
Faciliate high specimen throughput
57
What kind of systems are used for bood cultures?
Fully automated continuous monitoring systems e.g. BacT/Alert 3
58
What is the principle of the BacT?
Colorimetric detection of CO2 production
59
What is the maximum blood volume for the BacT?
10mmls
60
What are some factors that affect pathogen recovery on automated BC systems?
Method of collection
Number and timing of samples
Volume of sample - underfilled/overfilled
Media used
Neutralisation of antimicrobial agents through resin
Incubation time and temperature
Agitation of media
Headspace atmosphere
61
Why is the collecting of BCBs so important?
Need to collect three sets taken at three separate time points
Both aerobic and anaerobic bottles should be taken
Should be taken when temperature is peaking/on the rise
62
How should a BSB sample be taken?
Collect blood sample via venepuncture site
Disinfect skin and septum of blood culture bottle with alcohol and air dry
Take blood sample and divide between aerobic/anaerobic )and fungal bottle if necessary)
63
At what time should BCB be taken
Before antimicrobial therapy where possible
As soon as possible after a spike of fever
- except for query endocarditis
64
What is different about taking a babies BCB
Blood can be taken from baby's toe -> same applies to intravenous drug users with collapsed veins
65
Why do we take 3 blood culture bottle sets?
These are taken to allow for recognition of contaminants
They are taken at 3 separate time points over several hours or days - this increases yield
66
What are the most common BSI contaminants?
Coagulase-neg staphs
S. viridans
Diptheroids
67
What is the most critical factor in blood culture collection?
Volume -> underfilled vs overfilled
68
What is the most critical factor in blood culture collection?
Volume -> underfilled vs overfilled
69
Why is volume the most critical factor in blood culture filling?
There is a direct relationship between blood volume and yield
20-30mls of blood are recommended for culture (total volume)
10mls of sample should be added to bottles
70
Explain the relationship between blood volume and bacterial yield
Direct relationship
Per 1ml of blood there is a 3% increase in yield -> overfiled can result in too many leucocytes which can cause false positives??
71
How many mls of neonatal blood needed for culture
Only 0.5-2.0mls needed
The magnitude of childhood BSI is usually higher than in adults
*Never take no more than 1% of a childs blood
72
What is in a basic BC set?
Standard aerobic bottle + anaerobic bottle
Each contains 40mls of Tryptic Soy Broth Agae (TSB) Media +/- resin or activated charcoal
73
What is in a basic BC set?
Standard aerobic bottle + anaerobic bottle
Each contains 40mls of Tryptic Soy Broth Agae (TSB) Media +/- resin or activated charcoal
74
What is in a paediatric BC set?
20/30mls of peptrone enriched Tryptic Soy Broth agar
-> enriched TSB agar
Supplemented with brain/heart infusion solids (BHI) and activated charcoal
75
Why do we enrich paed BC bottles with BHI solids and charcoal?
These improve microbial recovery by absorbing antimicrobials
76
Why do we enrich paed BC bottles with BHI solids and charcoal?
These improve microbial recovery by absorbing antimicrobials
77
What media is used for Mycobacteria?
Middlebrook 7H9 broth
78
What is the ideal ratio of components of BC bottles?
Blood to broth ratio of 1:15
- needed to counteract antimicrobial effects
Blood to broth ratio of 1:5 with the addition of other specific agents that inhibit antibacterial properties
79
What is the resin used in blood culture bottles?
Resin in the forms of free-floating beads
These mop up and eliminate any antibiotics that ma be present to increase sensitivity
They also provide a larger surface area for bacterial adhesion and replication
This facilitates lysis of host cells and the release of intracellular organisms
80
What is the activated charcoal used in BCBs?
This enhances microbial recovery by absorbing antimicrobials creating a more favourable environment for bacterial growth
81
What incubation is optimal for blood cultures?
35-37 degrees celsius for 5-7 days for routine cultures - optimal for most organisms
extended incubation if query endocarditis or Brucellosis/other fastidious organisms or fungi
82
Why do a lot of places no longer extend blood cultures for query endocarditis anymore?
There has been a lot of research that proves this extenstion may be pointless
83
Why do a lot of places no longer extend blood cultures for query endocarditis anymore?
There has been a lot of research that proves this extenstion may be pointless
84
If you query a Brucella BSI what should you do?
10 days + extended incbation
Terminal subculture even if still negative
85
What safety considerations should you take when processing blood cultures?
Subculture must be performed in a safety cabinet
-> if query brucella then in cat 3
sub-vent units for subculturing is preferred
Venting needles are now plastic and not metal as there was a lot of needle stick injuries with lab staff
86
What care shouhld be taken between taking sample and loading it onto system?
Blood cultures should be transported to lab as soon as possible
Specimens should be loaded onto system as soon as possible
Sample can only be at room temperature for a max of 4 hours
Ambient temperature is preferable ro refrigeration
* BCB not to be incubated at 37 degreses -> this can cause you to miss a positive
87
What care shouhld be taken between taking sample and loading it onto system?
Blood cultures should be transported to lab as soon as possible
Specimens should be loaded onto system as soon as possible
Sample can only be at room temperature for a max of 4 hours
Ambient temperature is preferable ro refrigeration
* BCB not to be incubated at 37 degreses -> this can cause you to miss a positive
88
What did the BacT virtuo do with negative bottles?
If a bottle was negative after 5 days incubation the virtuo would simply throw the bottle off
Virtuo would let the LIS system know that the bottle was negative
Scientist will just have to report it
89
What is the main reason for having to reject blood culture bottles?
Doctors tend to send down blood cultures in batches
This means a bottle could have been left at room temp for more than 4 hours by the time we receive it in the lab
90
How long should you leave a positive blood culture on the bacT, why is this significant?
Never leave a blood culture for more than 4 hours on the BacT
Certain organisms such as S. pneumo will undergo autolysis - this will result in a negative gram from these positive cultures
91
What is done with positive blood cultures?
Gram and culture
92
How do you gram and culture directly from a blood culture bottle?
Invert the positive bottle gently to mix contents
Wipe the septum of the bottle with 70% ethanol and allow to air dry
Using the safety, venting unit inoculate the agar plates: Blood, Chocolate, MH and MacConkey
Add your ring of blood cultture antimicrobials to the muller hinton plate
Inoculate a clean microscopy slide and allow to dry for gram
93
What culture plates are put up or blood cultures
Always blood anaerobically with MTZ and chocolate in CO2 both at 37 degrees and ready daily
Additional plates include Muller Hinton, MacConkey
Candida chrom agar or malt agar for query yeast
Chromagar for query GNB
Bile aesculin for query enterococci
etc etc
94
What do we do for a query staph in blood culture?
MH + cefoxitin
MRSA = cefoxtin resitant
95
What do we do with a query S. pneumo in blood culture?
Slide latex pneumo test directly from blood culture
Can put up blood + optochin
96
What antimicrobials are put up on Muller Hinton agar, why these?
Cefoxitin
Vancomycin
Ciprofloxacin
CPD (cefpodoxime)
Meropenem
TZP (piercillin/tazobactam)
These are not for a treatment plan they are just for notifying resistance
97
How do we carry out AST for blood cultures?
(3)
We do AST straight from blood culture bottles, no subbing - direct AST
We cannot standardise the inoculum when using drops of blood so AST is only for guidance - prelim report
All suceptibility is repeated the following day with bacterial colonies from culture either by disc diffusion or E test or on Vitek
98
Why do we do AST directly from blood culture bottles, why is this significant?
it is done to save time due to the serious nature of a blood stream infection
We can have a preliminary guide report out a day earlier than full AST
99
What should a scientist doo with a positive blood culture vs negative
Positive culture:
- if gram positive phone results ASAP
- issue preliminary culture report
- when culture complete issue a final authorised report (after maldi ID)
Negatives:
- negative report is issues at 5 days and 7 days
- negatve final report issues for suspected IE culures still negative at 21 days
100
What are the two main reasons for false positive blood cultures?
Metabolic activity of WBCs
Lysis of bacteria e.g. autolysis of S. pneumo
101
What happens with S. pneumo o blood cultures
They grow but then they start to autolyse
By the time you take an S. pneumo off and look at gram the gram might already be negative
You will still incubate the plates but these also might still be negativ
102
How do you interpret a BacT growth chart?
A sigmoid curve = positive growth
A constantly increasing curve which doesnt flatline = high white cells
Flatline = negative
103
How do you deal with false positives due to high white cells?
These bottles will prematurely flag positive
The bacT will unload these thinking they are positive
Scientist will have to read growth chart and determine high whites and reload bottle
Bottle will have to be repeatedly reloaded until 5 days incubation is complete - this can be a pain
104
How often is contamination seen in blood culture bottles
Before Leen Six Sigma and scientists with LEEN belts there was a lot more contamination:
- Between 15 and 30% of bottles were contaminated
With leen processing we not have special blood culture kits with sterile gloves and more training etc which has greatly reduced contamination
- Now only between 2 and 5% of bottles
105
What are the most common contaminating organisms?
Skin flora:
- CNS (70% of contamination)
- Diptheroids
- Bacillus species
106
How can we determine if an organism is a contaminant or not?
The type of organism (is it a skin flora organism)
No of bottles positive -> across all bottles or just one set
How long did it take to go positive - 5 days usually for a contaminant but only 48hrs for a tru BSI
Clinical information - could this be infectious etc
107
What is the gold standard for detection of BSI pathogens
Blood culture
108
How sensitive are blood cultures?
Low positivity rate: only between 30-40%, 60% at best of BSI are blood culture positive
109
Why is the positivity rate for blood cultures so low?
Mostly due to patients being on antimicrobial treatment
Slow growing fastidious organism
110
Other then poor positivity rate, what is the main pitfall of blood cultures?
The slow TAT
It takes atleast 24 hours for a preliminary ID -> if culture positive within 24hours - but usually its 48
Takes an additional 24hours to have AST guide and another day to have full AST
- very slow TAT
111
Why are so many blood culture samples contaminated with antimicrobials?
For every hour that the treatment of a BSI is delayed there is a 7% increase in patient mortality
Because of this clinicians are absolutely not waiting around for blood cultures, they are treating the patient ASAP
Even if culture negative the clinicians will still treat the patient if there is high enough suspicion
112
What are the three novel approaches to BSIs being looked at?
FISH
MALDI-TOF
Multiplex PCR both direct and indirect
113
What does FISH stand for?
Fluorescence In Situ Hybridisation
114
What is FISH?
A molecular diagnostic technique used to detect bloodstream infections by identifying the presence of pathogens directly in blood culture samples
It works using fluorescntly labelled probes that specifically bind to unique sequences of the taget organisms RNA or DNA
115
Talk about the use of FISH for blood cultures
Can detect 20-25 pathogen species responsible for over 90% of BSI
Uses fluorescently labelled oligonucleotide probes specific for 16S rRNA designed for most of these pathogens
It can improve the speed of pathogen identification, it is often used alongside other diagnostic methods to overcome these limitations - but still need to culture for AST
116
What are the main pros of FISH for BSI detection
Rapid identification within hours after a positive BCB
Direct detection striaght from BCB
Highly specific probes
Very effective for fastidious/slow-growing organisms
Can detect bacteria and fungi
Complementary to other techniques such as MALDI-TOF and PCR
117
What are the cons of FISH for BSI detection
Limited target range - cant detect 10% of organisms causative of BSIs - only has certain targets
Cannot detect antibiotic resistance - AST still needed
Requires a positive blood culture - 24-48 hours wasted
Higher cost - probes are expensive compared to agar
Skilled personnel needed to interpret results
False negatives due to genetic mutations in target regions - probes wont bind
Limited quantification - can only detect if present or now etc
118
How can MALDI be used for Blood cultures
Maldi can be used in two ways:
- by IDing from actual isolates/colonies done on a quickly grown first inoclum
- Directly from positive blood culture
119
How do we use the MALDI to ID organisms straight from blood culture?
Microboial cells are harvested from blood culture
Cells are processed using the MALDI Sepsityper Kit
Cells are then identified by the MALDI Biotyper 3.0
120
What are the pros and cons for using MALDI-TOF for BC
Rapid TAT following flags positive 20-70mins
Still have to wait for growth in blood culture bottles (but not sub plate)
Have to culture for sensitivities
Sensitivity of 76% but specificity of 96%
121
What organisms does the MALDI-TOF struggle to ID from blood cultures
CNS: 24-97% sens
Enterococcus: 50-70%
Strep: 32-50%
It also struggles with polymicrobial infections
122
What are the main benefits of the MALDI-TOF for BC ID
reduced TAT
Relatively cheap, less than 25 euro a test
123
In reality very few labs use the sepsityper kit with MALDI, what do we do instead
A lot of labs do short-term incubation on solid media for blood cultures
Blood cutures positive in morning - streaked early on - growth till later in the day
GPCs and GNBs only take about 6hours to start growing
First inoculum starts to grow after a fw hours - hazy growth - can be IDd from this
124
What PCR do we use for blood cultures?
Film array BC Id panel (we didnt have this in the mater)
This was used in the maternity hospitals not so much clinical hospitals (only put up really at request of docs)
125
What targets are there on the film array for BCs
24 targets total:
- 8 gram positive
- 11 gram negativ
- 5 yeast
2 antimicorbial resistance genes (mecA, vanA/B and bla kp)
126
Compare the film array vs maldi-tof for bc id
Film array is more accurate (91% vs 81%)
Film array is quicker (+2.4hrs vs 2.9hrs after positive virtuo)
Film array can detect some resistance genes, maldi cannot
Film array is way more expensive (120 euro vs 25 euro)
127
What PCR methods can be used to indirectly test on blood
(3)
Lightcycler SeptiFast Test
SepsiTest
IRIDICA BAC BSI assay
128
Talk about the Lightcycler SeptiFast Test for Blood Cultures, what kind of PCR is it, pros and cons.
Designed to detect and identify the 25 most important bacterial and fungal species causing BSI within 6 hours
It is a 3x multiplex amplificatin reaction: gram pos master mix, gram neg master mix and fungal master mix
Only needs 1.5mls of blood to extract DNA
TAT of only 6 hours total!!
Expensive at about 200 euro a test
Can only detect expected pathogens
129
Talk about the SepsiTest for direct BSI detection. what kind of sequencing, sample type, pros and cons, compare to light cycler
1ml of EDTA-treated whole blood
Universal PCR and Sanger sequencing
Id species >200 genera bacteria and 65 genera of fungi
Costs about 190 euro
TAT of 8 hours
(more sensitive than LightCycler, slightly less expensive, a little slower)
130
Talk about the IRIDICA BAC BSI assay for direct BSI detection, sample type, PCR type, targets, pros/cons, compare to other methods
5mls of EDTA-treated whole blood
Combines broad-range PCR + electrospray ionisation MS
Also detects mecA, vanA, vamB and blKPC determinants
Detects over 780 bacterial and candidal species
Costs about 235 euros for test
TAT of 6 hours
Most amount of targets, but most expensive, short TAT though and can detect resistance
131
Why do we not use Septifast or SepsiTest in Ireland
When compared to blood culture the Septifast had a sens of 50% while the sepsitest had a 48% sense
- very low sensitivity which didnt meet hospital criteria
132
Why do we not use the IRIDICA in ireland
When compared to BC the IRIDICA had a sens of 81% -> good sens
IRIDICA has the potential to greatly decrease TAT but it is really expensive at the moment
There also hasnt been enough evidence to prove that this reduced TAT actually impacts the treatment of the patient -> patients treated with broad spectrum antibiotics usually anyways as soon as BC positive is phoned (if not before) -> still have to wait for AST to switch to different antibiotics
133
In general what are the limitations of PCR for BSIs
Low diagnostic sensitivity
High cost
Interpretation problems
- CNS and streptococci (contaminants vs infectious)
- DNAemia but not a BSI
No proven benefit on patient treatment, mortality, hospital stay etc
134
What are the potential benefits of direct PCR for BSIs
Its better than conventiona BC -> BC has low sensitivity - PCR isnt great sensitivtiy but it is better than this
PCR is much better for anti-microbial pre-treated patints
PCR is preferred for immuno-compromised patients
PCR is preferred for neonatal sepsis - quick TAT
PCR is best used when combined with positive blood cultures
