interpretative reading (4)

7/28/2019 Interpretative Reading (4)

1/11

INTERPRETATIVEREADING

Tan Thean Yen

To Interpret

interpret

explain the meaning of

(information, words, or

actions)

To Interpret

analyse susceptibility results

based: organism identificationall antibiotic results (pattern)

interpret susceptibility based on above

Courvalin P. Interpretive reading of in v itro antibiotic susceptibility tests (the antibiogramme).

Clinical Microbiology and Infection. 1996;2:S26S34.

Why interpret?

To detect unusual results that need further

testing or confirmation

To report appropriate antibiotic results for the

organism-infection combination

To detect emerging resistance


2/11

Description of action to be taken, based on

current evidence, in response to specific

antimicrobial susceptibility test resultsEX

PERT

RULE

Expert rule

If you obey all of the rules, you miss all of the fun.

- Katharine Hepburn

Actions

Recommendations on reporting

Inference of susceptibility

Edit results from S to I or R, from I to R,but NEVER I or R to S

Suppression of results

Addition of comments

Advice on further tests

Advice on referral of isolates

EX

PERT

RULE

Brown, D. Concepts and needs for expert rules and intrepretive reading of the antibiogram. The EUCAST perspective

Requirements

Identification of the organism (fully)

May need to test an extended range of

appropriate antibiotics

Access to a set of expert rules

EXPER

T

RUL

E

Three areas to cover

1. Intrinsic resistance

2. antibiogram reading

3. Exceptional phenotypes


3/11

INTRINSIC RESISTANCE

Part One

Chromosomal

(born with it)

INT

RINS

IC

RE

SIST

ANCE

resistance which is a

characteristic of thespecies

Susceptible results?

errors in identification or

susceptibility testing

drug should be used withcaution

IN

TRI

NSIC

RESIS

TAN

CE

ExamplesOrganism Antibiotic resistance

Enterobacteriaceae Vancomycin

Gram-positive organism Aztreonam

Klebsiella species Ampicillin

Proteus mirabilis Nitrofurantoin

Polymyxins

Serratia marcescens Polymyxins

Livermore DM, et al. Interpretative reading: recognizing the unusual and inferring resistance mechanisms from resistance phenotypes.

J Antimicrob Chemother. 2001 Jul 1;48(suppl 1):87102

IN

TRI

NSIC

RESIS

TAN

CE


4/11

INT

RINS

IC

RE

SIST

ANCE

http://www.eucast.org/expert_rules/

ANTIBIOGRAM READING

Part Two

Test susceptibility

Infer resistance mechanism

Interpret clinical susceptibility on the basis

of the resistance mechanism

AN

TIB

IOGRA

M

REA

DIN

G

Canton, R. Expert Rules In Susceptibility Testing Rationale, Advantage And Disadvantages.

ECCMID 31 March-3 April, 2012

EXPER

T

RUL

E

Species identification

Antibiotic susceptibility

REPORT


5/11

EX

PERT

RULE

Species identification

Antibiotic susceptibility

Antibiogram

interpretation

REPORT

deduce phenotype

deduce biochemical

resistance

clinical

relevance

additional

tests

1. re-define susceptibility

(categorical)

2. deduce susceptibility to

non-tested antibiotics

3. clinical comments

4. clinical advice

Simple..

Staphylococcus aureus

Result: resistant to cefoxitin

Infer: resistance mediated by mecA

Interpret: resistant to all beta-lactams

ANT

IBIO

GRAM

READ

ING

More complicated..

Enterobacteriaceae

Result: tobramycin non-susceptible

amikacin & gentamicin susceptible

Infer: acquired AAC(6)-I enzyme

Interpret: report amikacin as Intermediate

AN

TIB

IOGRA

M

REA

DIN

G

Escherichia coliAN

TIB

IOGRA

M

REA

DIN

G

Antibiotic Category

Ampicillin R

Amoxicillin-clavulana te S

Piperacillin-tazobactam S

Cephalothin R

Ceftriaxone R

Ceftazidime S

Cefepime R

Cefoxitin S

Ertapenem S

Gentamicin S

Amikacin S

Ciprofloxacin S

Trimethoprim-sulfamethoxazole S

Infer:

Extended spectrum beta-lactamase(CTX-M)

Interpret:

Consider reporting ceftazidimeas

resistant

OR

Reporting presence of ESBL with

comment


6/11

Klebsiella pneumoniaeANT

IBIO

GRAM

READ

ING

Infer:

ampCenzyme

(plasmid-acquired)

Interpret:

Consider reporting ceftriaxone as

resistant

Antibiotic Category

Ampicillin R

Amoxicillin-clavulana te R

Piperacillin-tazobactam S

Cephalothin R

Ceftriaxone I

Ceftazidime R

Cefepime S

Cefoxitin R

Ertapenem S

Gentamicin S

Amikacin S

Ciprofloxacin S

Trimethoprim-sulfamethoxazole S

Limitations

High complexity of resistance mechanisms

Limited information about some mechanisms of

resistance

Multifactorial multiresistance

Oversimplification of interpretative reading

Mistakes when deducing mechanisms ofresistance

EXCEPTIONAL PHENOTYPE

Part Three

Resistance in a species

where resistance has not

been seen or is rare

may change with time

may also be regional or national

differences

EXC

EPT

IONAL

PHEN

OTY

PE


7/11

Resistance in a species

where resistance has not

been seen or is rare

errors in identification or

susceptibility testing

send the isolate to a reference

laboratory for independentconfirmation

EXCE

PTIO

NAL

P

HENO

TYPE

Streptococcus pyogenes resistant to penicillin

Staphylococcus aureus resistant to vancomycin

Haemophilus influenzae resistant to any third-

generation cephalosporin, carbapenems, and

fluoroquinolones

EXCE

PTIO

NAL

P

HENO

TYPE

Examples

Anaerobes

resistant to metronidazole

Neisseria gonorrhoeae

resistant to third-generation cephalosporin

Enterobacteriaceae

resistant to carbapenems

EXC

EPT

IONAL

PHEN

OTY

PE

Examples

HOW TO BE AN EXPERT


8/11

ICU patient28 days in hospital

oxidase negative

non-fermentative Gram-

negative bacillus

ICU patient

28 days in hospital

oxidase negative

non-fermentative Gram-

negative bacillus

Antibiotic Zone(mm)

Result

Amoxicillin-clavulana te 6 R

Piperacillin-tazobactam 6 R

Ceftriaxone 6 R

Ceftazidime 26

Cefepime 18

Imipenem 6 R

Ertapenem 6 R

Meropenem 6 R

Amikacin 6 R

Gentamicin 6 R

Ciprofloxacin 30

Trimethoprim-sulfamethoxazole

35

What is the likely organism?

How would you report

susceptibility to:

ceftazidime

imipenem

ciprofloxacin

Antibiotic Zone(mm)

Result

Amoxicillin-clavulanate

6 R

Cefoxitin 6 R

Ceftriaxone 27 S

Ceftazidime 26 S

Cefepime 24 S

Imipenem 24 S

Ertapenem 23 S

Meropenem 24 S

Ciprofloxacin 25 S


20 S

Enterobacter cloacae

Isolate from blood culture

Patient with suspected ventilator-

associated pneumonia


9/11

Antibiotic Zone(mm)

Result

Amoxicillin-clavulanate

6 R

Cefoxitin 6 R

Ceftriaxone 27 S

Ceftazidime 26 S

Cefepime 24 S

Imipenem 24 S

Ertapenem 23 SMeropenem 24 S

Ciprofloxacin 25 S


20 S

Enterobacter cloacae

Isolate from blood culture

Patient with suspected ventilator-

associated pneumonia

How would you report

susceptibility to:

ceftriaxone

cefepime

imipenem

ARTIFICIAL INTELLIGENCE

Computerised expert

modificationDisc susceptibility

Adagio

Biomic

MIC equivalent

Phoenix

Vitek

Microscan

Vitek AES

Changed

cefepime to

Resistant


10/11

Lab Information System Alerts

The Real Expert Summary

Systems vary in accuracy

design

update frequency

See

Winstanley T, Courvalin P. Expert Systems in

Clinical Microbiology.Clin Microbiol Rev. 2011; 24(3):51556.


11/11

Conclusions

Some resistant organisms may need

supplemental methods to detect

Susceptibility testing can be complicated

Resistance mechanism or tested MIC?

Not yet quite sure.

interpretative reading (4)

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