Transcript How to prescribe antibiotics: maybe it’s not as simple as

Microbiology Nuts & Bolts
Test Yourself - Sepsis
Begin here
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The patient in this test yourself case is
entirely fictitious, however it is based
on many clinical scenarios the author
has come in to contact with during his
medical career. Any similarity to a real
case is entirely coincidental.
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Carla
• 45 year old lady with a history of breast cancer
• She last had chemotherapy a week ago
• She presents with a fever and shortness of
breath
• On examination she is tachycardic and
hypotensive
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What is the most likely diagnosis?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Urinary tract infection
Community acquired pneumonia
Cellulitis
Sepsis
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Correct
• Answer: Sepsis
• At this stage the most that can be said about Carla is that
she is probably septic
• Sepsis is infection with evidence of the systemic response
to that infection
• Sepsis is a medical emergency
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Carla
• Carla is seen immediately by the medical team
and given oxygen and fluids
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What blood sciences investigations
should be done?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
FBC,
FBC,
FBC,
FBC,
U&Es, CRP
Clotting, U&Es, LFTs, CRP
Clotting, U&Es, LFTs, blood gas
Clotting, U&Es, CRP, blood gas
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Correct
• Answer: FBC, Clotting, U&Es, LFTs, CRP, blood gas
• There may be other tests required as well but these are a bare
minimum to manage to diagnose sepsis and manage this patient
effectively
• The blood sciences tests involved in diagnosing severe sepsis
include:
–
–
–
–
–
–
Total white blood cell count
Platelet count
Bilirubin
Creatinine
INR or APTT
Lactate
• CRP is not part of the sepsis diagnostic criteria, and can be
normal in rapid onset sepsis
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Which of the following is NOT a
common cause of sepsis?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Neisseria meningitidis
Staphylococcus haemolyticus
Streptococcus pyogenes
Klebsiella pneumoniae
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Correct
• Answer: Staphylococcus haemolyticus
• Despite it’s serious sounding name S. haemolyticus is actually
one of the Coagulase-negative Staphylococci and these very
rarely cause sepsis
• The most common causes of sepsis include:
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–
–
–
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Neisseria meningitidis
Staphylococcus aureus
Enterobacteriaceae e.g. E. coli, Klebsiella spp., Enterobacter spp.
Pseudomonas aeruginosa
Streptococcus pyogenes
• Sepsis can arise from infection in almost any body site
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Carla
• Carla was diagnosed with severe sepsis
• Blood cultures were taken
• Antibiotics were started within the first hour of
her admission to hospital
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Which blood culture bottle should be
taken first?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Aerobic
Anaerobic
It doesn’t matter
Other blood tests should be taken first
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Correct
• Answer: Aerobic
• Blood cultures should always be taken before other blood
samples, because the other blood sample collection
containers are not sterile
• If the needle from the venepuncture equipment is
contaminated from the other blood sample containers
then the contaminating bacterium can grow in the blood
culture causing a false positive result, also known as a
pseudobacteraemia
• The aerobic bottle should be taken first as this is most
likely to grow a pathogen
– Most human pathogens are either aerobes or facultative anaerobes,
in either case the bacterium will grow in the aerobic bottle
– Aerobes will not grow in the anaerobic bottle, and infections only
caused by anaerobes are uncommon, and usually the blood cultures
are not positive in these infections anyway
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Which of the following would be
appropriate empirical antibiotic(s)?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
IV
IV
IV
IV
Ceftazidime
Teicoplanin
Gentamicin
Piptazobactam
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Correct
• Answer: IV Piptazobactam
• Of the antibiotics listed, only Piptazobactam has a sufficiently
broad enough spectrum of activity to cover all of the common
causes of sepsis
• IV Gentamicin is often added to other antibiotics to treat sepsis
because it has excellent bactericidal activity against
Staphylococcus aureus, Enterobacteriaceae and Pseudomonas
aeruginosa
• Ceftazidime does not have adequate activity against Grampositive bacteria
• Teicoplanin has no activity against Gram-negative bacteria
• Gentamicin on it’s own does not cover Neisseria meningitidis or
Streptococci
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Carla
• The blood tests reveal that Carla is neutropaenic
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What is the correct decision about
antibiotic therapy now?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Continue IV Piptazobactam
Add IV Clarithromycin
Change to IV Meropenem
Add IV Teicoplanin
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Correct
• Answer: Continue IV Piptazobactam
• IV Piptazobactam covers the common causes of sepsis
irrespective of whether the patient is neutropaenic or not
• It is not necessary to change the antibiotics in response to
the current blood test results
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Carla
• The blood cultures taken from Carla are taken
down to the microbiology laboratory
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How are blood cultures processed in
the microbiology laboratory?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Urgent Gram film then culture
Plated to agar for culture
Loaded on to automated incubator
Left at room temperature to enhance growth
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Correct
• Answer: loaded on to automated incubator
• The number of bacteria in a blood culture from a patient who is
septic is actually very low, about 1 colony forming unit (or
bacterium) per ml of blood
• It is therefore necessary to grow these bacteria up to sufficient
numbers to be able to identify the bacterium and perform
antibiotic sensitivities
• The blood cultures are loaded on to an automated incubator as
soon as possible so that the cooler temperature of a normal
room doesn’t kill the bacteria
• The automated incubator scans the bottles every 10 minutes in
order to detect the production of carbon dioxide from living
bacteria
• Once the incubator indicates the blood culture is positive the
bottles are taken off the machine and further work begins
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Carla
• Two days after admission no longer septic
• White blood cell count improving, no longer
neutropaenic
• Remains febrile
• Worsening shortness of breath
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Chest X ray
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What is the likely diagnosis?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Pneumococcal pneumonia
PCP
Viral pneumonitis
Invasive fungal infection
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Correct
• Answer: Invasive fugal infection
• The most likely diagnosis based upon the chest x-ray
appearances and the lack of response to Piptazobactam is an
invasive fungal infection
• Streptococcus pneumoniae would be expected to respond to
Piptazobactam
• PCP and viral pneumonitis would have a more “ground glass”
appearance
• Carla would no longer appear septic because her white cells are
recovering from the chemotherapy and are starting to fight the
infection
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Carla
• A subsequent CT chest also shows a likely
invasive fungal infection
• The most likely fungus is Aspergillus spp.
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Which test would be most useful on a
bronchoalveolar lavage (BAL) sample?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Beta-D-glucan
Laboratory culture
Galactomannan
Grocott silver stain
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Correct
• Answer: Galactomannan
• All of the tests are of potential value in the diagnosis of invasive
fungal infections but Galactomannan is the most useful for
invasive aspergillosis
• Galactomannan is an antigen from the Aspergillus spp. cell wall
which can be detected in both BAL and blood samples
• Detection of galactomannan in a BAL sample has a positive
predictive value of 89%, a negative predictive value of 95%
• The PPV and NPV for the other tests is much lower
• Molecular tests (PCR) either alone or in combination with
galactomannan are the best tests but they are expensive and
not widely available
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Carla
• A galactomannan on a BAL sample confirms
invasive pulmonary aspergillosis
• Carla is started on antifungal treatment
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Which of the following is NOT active
against Aspergillus spp.?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Amphotericin B
Fluconazole
Caspofungin
Voriconazole
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Correct
• Answer: Fluconazole
• Fluconazole has no useful activity against moulds such as
Aspergillus spp. and should be regarded as treatment of
Candida spp.
• All of the other drugs have activity against Aspergillus
spp. although Voriconazole is regarded as the most active
• Voriconazole has a lot of side effects and drug interactions and
so it is not always possible to use it to treat patients
• Amphotericin B and Caspofungin are IV whereas Voriconazole is
available both IV and PO
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Carla
• Carla received 6 weeks of treatment for her
pulmonary aspergillosis and made a full
recovery
The End
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