Nosocomial Infections
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Transcript Nosocomial Infections
Role of the Microbiology
Laboratory in Hospital
Epidemiology
Karen C. Carroll, M.D.
Associate Professor, Pathology
Adjunct Associate Professor, Infectious
Diseases
University of Utah Medical Center
Nosocomial Infections
Infections not incubating on admission
to a health care institution (acquired
during a stay)
Infections may involve patients, visitors
or hospital personnel
Nosocomial
Infections:Impact
Major public health problem worldwide
Affects 5-10% of patients admitted to U.S.
hospitals-- 2 million patients annually
Significant annual expenditures-- $4.5
billion
Contribute significantly to morbidity and
mortality
– nosocomial BSI--25% attributable mortality
– 20,000 deaths annually from HAP
– catheter-related UTIs also contribute to risk of
dying
Major Types of Nosocomial
Infections
35
30
25
UTI
Pneumonia
SWI
Bloodstream
Other
20
15
10
5
0
Overall
ICU
Richards, MJ. 1999.
Crit Care Med 27; 887.
Nosocomial Infections:
Changing Microbiology
Mid-1980’s
– Enterobacteriaceae
– S. aureus
– P. aeruginosa
– CoNS
Mid-1990’s
– Decline in
Enterobacteriaceae
– Increase in grampositive cocci
– Emergence of fungi
– Recognition of
viruses
Major Pathogens Associated with each
Category of Nosocomial Infections
BSI
Pneumonia SSI
UTI
Pathogen (%) Pathogen (%) Pathogen (%) Pathogen (%)
CoNS
39 S. aureus 17 Enterococci 17 E. coli
19
S. aureus
12 P. aerug
16 CoNS
Enterococci 11 Enterobact 11 P. aerug
Candida sp. 11 K. pneumon 7 S. aureus
12 C. albicans 15
10 Enterococci 14
9 P. aerug.
10
Selected Antimicrobial Resistant
Pathogens: Nosocomial Infections in
ICU Patients
Resistance Pattern
2000 Resistance
Rate (%)
% Increase in
Resistance
26
1995-1999
Resistance Rates*
(%)
14-25
Vanco/Enterococci
Meth/S. aureus
55
33-51
29
Meth/CoNS
87
85-88
1
rd
3
2-5
15
3 ceph/K. pneumo
rd
11
9-11
5
Imipenem/P. aerug
18
12-16
23
Quinolone/P. aerug
27
12-23
53
26
35
19-23
33-37
24
-1
3 ceph/E. coli
rd
3 ceph/P. aerug
rd
3 ceph/Enterobact
31
*Mean rates +/- one standard deviation. CDC website NNIS ICU data. AJIC 29:410, 2001.
Role of the Microbiology
Laboratory
Grow and detect microbial pathogens
Identify causative organisms rapidly
and accurately to species level
Perform accurate susceptibility testing
– Recognize limitations of automated
methods
– Provide supplemental testing for problem
bacteria
– Recognize and survey for MDR organisms
Glycopeptide Intermediate
S. aureus
All labs should have a procedure for
selection of S. aureus strains for
additional testing
– S. aureus with MICs > 4 g/ml
– S. aureus with MICs > 8g/ml
– Select and test all MRSA
– Select isolates growing on screening agar
BHI agar containing 6 g/ml vancomycin
Use inoculum of 106 cfu/ml
Glycopeptide Intermediate
S. aureus:Testing
Disk diffusion is unacceptable
MIC testing method should be used
– broth microdilution
– agar dilution
– agar gradient diffusion
Incubate for full 24h at 35° C
Use S. aureus ATCC 29213 as neg.
control strain
Send to State Lab/CDC for confirmation
– [email protected]
Role of the Microbiology
Lab
Timely reporting
“Early warning system”
Infection control critical values
–
–
–
–
–
–
Positive AFB smears and Mtb cultures
VRE
MRSA. GISA
Legionella
Salmonella/shigella
Multi-drug resistant GNR
Data summaries, monitoring trends
Direct Infection-Control Related
Functions: Micro Lab
Participate as a member of the
infection control committee
– Ensures communication
– Enhances education
– Allows for allocation of resources
Organize and report microbiology data
– Antibiograms
– Customized epidemiological reports
Store data and isolates
Direct Infection-Control Related
Functions:Micro Lab
Collaborate with IC personnel on
outbreak investigations
Perform standard typing tests
Serve as an educational resource
– basic microbiology training
– periodic updates: changes in technology,
taxonomy
Role of the Microbiology Lab in
Investigation of an Outbreak
Investigative Step
Laboratory’s Role
Recognize the problem
Form case definition
Look for additional cases
Calculate rates
Laboratory surveillance
Communication
Microbiologic confirmation
Store data and isolates
Characterize the outbreak
Who
Where
When
What
Characterize isolates
Type isolates
Assess number and location
Role of the Microbiology Lab in
Investigation of an Outbreak
Investigative Step
Laboratory’s Role
Consider possible causes
Define mode of transmission
Identify potential reservoirs
Identify potential vectors
Conduct supplementary studies
Cultures from personnel,
patients’ environment
Control/terminate the outbreak Adjust lab procedures to
Define/implement control
support control activities
measures
Continue lab surveillance
Evaluate efficacy of control
Store isolates
measures
Maintain communication
Continued surveillance
Application of Typing
Techniques
Epidemiological investigations
– increase in prevalence of infections due to
a particular species
– clusters of patients
– identification of isolates that have a
distinctive susceptibility pattern
Distinguishing relapse from re-infection
Establishing clonality of isolates
Epidemiologic Typing
Systems
Criteria for evaluation
Typeability
Reproducibility
Discriminatory power
Ease of interpretation
Ease of performance
Epidemiologic Typing Systems:
Classification
Phenotypic
Traditional
–
–
–
–
–
biotyping
antimicrobial susceptibility testing
serotyping
bacteriophage typing
bacteriocin typing
Protein-based
– multi-locus enzyme electrophoresis
– polyacrylamide gel electrophoresis of cellular proteins
– Immunoblot fingerprinting
Phenotypic Typing
Methods
Limitations
Influenced by environmental selective
pressure
– unstable antigenic traits
– alterations in expression of traits being assessed
Labor-intensive
Impractical
Slow
Lack discriminatory power
Epidemiologic Typing Systems
Classification
Genotypic methods
Plasmid analysis
Restriction endonuclease analysis
chromosomal DNA (REA)
Southern blot analysis of RFLP
Ribotyping
PFGE
PCR techniques
Sequence analysis
Gene expression--microarrays
Genotypic Typing
Methods
Limitations
Patterns generated may be complex
and difficult to interpret
Technically demanding
Methodology/ interpretation is not
standardized
PFGE Principles
Variation of conventional agarose gel
electrophoresis
Suspension of organism is embedded in
agarose plugs to minimize shearing of DNA
DNA is cut with restriction enzymes that
have infrequent recognition sites
Larger pieces of DNA are separated by
shifting direction of current frequently
5-20 fragments ranging in size from 10kb
to 800 kb in length are generated
Pulsed-Field Gel
Electrophoresis (PFGE)
Tenover Criteria for PFGE
Interpretation
Identical isolates--all bands match
Isolates are subtypes--patterns differ by
1 to 3 bands
Isolates are possibly related--patterns
differ by 4-6 bands
Isolates are unrelated--patterns differ
by more than 6 bands
Tenover FC, et. al. J Clin Microbiol 33:2233, 1995.
Modified Tenover Criteria
< 3 differences in restriction-fragment
positions
– could have occurred by a single genetic event
– may represent subtypes of the same strain
>3 restriction differences in restriction
fragment positions
– less likely to be epidemiologically related
Goering RV. In Rapid Detection of Infectious Agents, Specter, et.al.
(eds), Plenum Press, New York, 1998, p.131.
University of Utah Medical Center
VRE Outbreak
First isolate--mediastinal surgical wound
10 subsequent cases over 15 months in
MICU
Source of isolates
– blood--4
– urine or stool--4
– other sites--2
University of Utah Medical Center
VRE Outbreak
Characteristics of Isolates
All isolates were E. faecium, Van B
phenotype
Resistant to ampicillin, vancomycin,
ofloxacin, imipenem
HLR streptomycin, not gentamicin
Susceptible to teicoplanin,dalfopristinquinupristin, chloramphenicol
PFGE: Utility
Community Outbreaks
Hospital clusters
Laboratory contamination
Resolution of pseudo-outbreaks
Individual patient management
– Relapse vs. Re-infection
– Demonstration of persistence of infection
– Distinction between contamination vs..
infection
PFGE
Advantages
Patterns easier to
interpret compared to
other techniques
Highly reproducible
Excellent discriminatory
power
Theoretically all bacteria
are typeable, some
fungi as well
Disadvantages
Cost of equipment
Tedious
Slow
Certain organisms may
not be typeable e.g..
C. difficile, Aspergillus
sp
RiboPrinter® Microbial
Characterization System
RiboPrinter System
Features
Eight samples at a time; 32
samples/shift
Results in eight hours
Completely automated
Results stored electronically
Electronic sharing of data
PFGE vs. Ribotyping for VRE
Characterization
Study Objectives
Compare PFGE vs. ribotyping using two
restriction enzymes for VRE
94 total VRE isolates
– Late 1995 - mid-2000
– outbreak and non-outbreak isolates from
University of Utah
Automated Ribotyping:VRE Study
Two restriction endonucleases
simultaneously (1:1 mix of AseI and BamHI)
DNA electrophoresed and transferred to
nylon membrane (Southern Blot)
Probed for rRNA operon-specific DNA
fragments
Band pattern captured by CCD camera,
normalized and stored in computer memory
TAT of < 24 hours
Riboprint Patterns
Results
24 unique PFGE types
26 unique ribotype patterns
Multiple PFGE types - same
ribotype
– 2 instances
Single PFGE type - multiple
ribotypes
– 3 instances
Outbreak vs. Non-outbreak
Able to differentiate non-outbreak strain during an outbreak period. During the outbreak
involving PFGE type 11, PFGE type 16 was isolated. The RiboPrinter® System, using AseI and
BamHI simultaneously, was able to differentiate outbreak vs. non-outbreak associated strains
that were temporally related.
Isolate #
40.00
15.00
PFGE
8.00
6.00
3.00
4.00
2.00
1.00
RiboGroup
§ Non-outbreak associated strain
PFGE RiboGroup
Type
00-116-10237 .. ..
16
17
§
00-111-08430 .. ..
11
15
†
† Outbreak associated strain
Study Conclusions
Ribotyping using double RE digest
comparable to PFGE
PFGE able to discriminate subtypes
Ribotyping uses higher degree of
automation
Ribotyping has faster TAT
– more amenable to real-time characterization
Overall costs / sample are comparable
rep-PCR Core Technology
BACTERIA 2
BACTERIA 1
Primer
Primer
DNA Primer
DNA
Primer
DNA
DNA
DNA
DNA
Primer
Rep-PCR
Primer
DNA
Primer
Strain Differentiation
With reproducible fingerprints
Comparison of Competing
Technologies
Cultures
Subspecies
Discrimination
Low cost
Universal
equipment
Rapid
Universal
Primers
Reproducible
Database
capable
PFGE
X
AFLP
X
Ribotyping
X
X
repPCR
X
X
X
X
X
X
X
X
X
X
X
X
DiversiMap Phase I: Gel
Analysis
Epidemiologic Typing Methods
Basic Principles
Perform only with clear objectives
Variability exists in all methods
– evaluate all implicated isolates
simultaneously
– compare to epidemiologically unrelated
control isolates
Demonstrate not only relatedness of
clustered isolates, but differences
from isolates not involved
epidemiologically
Integrated Infection
Control Program
Active surveillance of high-risk patients
Incorporation of molecular typing into
routine surveillance
Weekly meetings to discuss trends
Information used to implement
appropriate infection control practice
– education of staff
– physical barriers
Integrated Infection
Control Program:Impact
Nosocomial infections decreased from
6.49/1,000 pt. days to 5.60/1,000 pt. days
Percentage of patients with nosocomial
infections dropped by 23%
Costs avoided averaged more than $2
million/yr.
Costs for the program paid by the hospital
– initial equipment/remodeling $180,050
– $400,000 annual costs for med techs
Peterson LR and Noskin GA. Emerg Infect Dis 7:306, 2001.
Expanded Roles of Infection
Control and Microbiology Labs
Infection Control
Shift toward focused
surveillance
– ICUs
– devices
– antimicrobial
resistance
Control strategies
are more proactive
– active intervention
– control of resistance
Microbiology Labs
Increasingly complex
and demanding work
– increasing resistance
– emerging pathogens
– new technology
Monitoring resistance
Implementation of
molecular
epidemiology