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Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Bioburden estimation of reusable and single use medical devices –
methodology and evaluation
Egil LingaasDepartment of Infection Prevention
RikshospitaletOslo
Norway
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Sterilization is a special process
The effectiveness of the process can not be fully verified by subsequent inspection and testing of the product
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Bioburden
Population of viable microorganisms on or in product and/or a package
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Origins of bioburden
● raw materials● manufacturing of components ● assembly process● manufacturing environment● assembly/manufacturing aids● cleaning process● packaging of finished products
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Use of bioburden determination
● Validation and revalidation of sterilization processes
● Routine monitoring of:● raw materials● components● packaging● manufacturing processes
● Assessment of the efficiency of cleaning processes
● Environmental monitoring
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Bioburden determination common as part of sterile production
Sterilization in industry
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Bioburden determination not common➨ In validation of sterile production➨ For routine monitoring
Medical devices– Multiple use– Single use
Sterilization in hospitals
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Microorganisms on surgical instruments
0
20
40
60
80
100
120
< 10 > 10 > 100 > 1000
CFU per instrument
Pro
po
rtio
n o
f in
stru
men
ts (
%)
Before w ashing
After w ashing I
After w ashing II
Modified from Nyström B. J Hosp Infect 1981;2:363
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Bioburden on surgical instruments before sterilzation
Modified from Rutala WA, et al. AJIC 1998;26:143
0
1020
30
40
5060
70
80
0-10 11-100 > 100
Microorganisms per instruments (CFU)
Pro
port
ion
of in
sttr
umen
ts (%
)
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Bioburden on surgical instruments after use and after washing
0
5
10
15
20
25
30
35
< 10 10-100 100-1000 1000-10000
CFU
Num
ber o
f ins
trum
ents
After use
After washing
Modified from Chu NS, et al. AJIC 1999;27:315
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Change of bioburden on surgical instruments during washing
Modified from Chu NS, et al. AJIC 1999;27:315
02468
10121416
-3 -2 -1 0 1 2 3
Log10 change
Num
ber o
f ins
trum
ents
Increase: 45%Decrease: 32%
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Non-medical devices– Multiple use– Single use
Bioburden determination and sterilization in hospitals
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
ISO 11737 Sterilization of health care products
- Microbiological methods
Part 1: Determination of a population of microorganisms on product
Part 2: Tests of sterility performed in the validation of a sterilization process
Part 3: Guidance on evaluation and the determination of bioburden data
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Selection of product
● Representative of the batch● Whole product, if feasible● If not: As large a portion as possible
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Selection of an appropriate method
● Removal of microorganisms● Culturing● Enumeration● Characterization
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
TECHNIQUES FOR REMOVAL OF MICROORGANISMS
FROM PRODUCT
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Adhesion of microorganisms to surfaces
● Surface characteristics● Microorganisms involved● Origin of contamination● Presence of other substances
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Removal techniquesRemoval techniques
● Stomaching● Ultrasonication● Shaking (mechanical or manual)● Vortex mixing● Flushing● Blending (disintegration)● Swabbing
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Removal techniquesRemoval techniques
● Stomaching● Ultrasonication● Shaking (mechanical or manual)● Vortex mixing
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Removal techniquesRemoval techniques
● Stomaching● Ultrasonication● Shaking (mechanical or manual)● Vortex mixing● Flushing● Blending (disintegration)● Swabbing
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
EluentsDiluentsTransport media
No proliferation or inactivation of microorganisms
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Eluents and diluents
● Sodium chloride 0.25 – 0.9 %● Ringer● Buffered peptone water● Phosphate buffered saline● Thiosulphate Ringer● ---------------● ---------------
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Additives to eluents and diluents
● Surfactant●Polysorbate (Tween) 80
● Neutralizers for microbicidal and microbistatic substances
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Release of substances from product
Substances released into suspending fluid should neither promote nor inhibit the growth of microorganisms
bacteriostasis test
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Methods where removal of Methods where removal of microorganisms is not employedmicroorganisms is not employed
● Contact plating● Agar overlaying
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Membrane filtration
● Filtration of an eluent followed by incubation of the filter on appropriate growth medium
● Plates are incubated
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Membrane filtration
Particularly useful for:➨ Suspensions with low concentrations of microorganisms
➨ Suspensions with microbicidal or microbistatic substances
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Pour plating
● Defined aliquots of suspension mixed with molten agar medium at 45 oC
● Agar allowed to solidify in the plate
● Plates are incubated
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Spread plating
● An aliquot of defined volume is spread on the surface of a nutritient medium
● Plates are incubated
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Spiral plating
● A defined volume spread in a spiral track on a rotating agar plate
● Plates are incubated
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Media and incubation conditions
Several combinations of media and incubation conditions are usually required
BacteriaYeasts and mouldsAnaerobic bacteria
30 - 35 oC20 - 25 oC
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
● Detecting small colonies ● Counting and reporting unusual colonies
e.g. spreaders● Enumerating and reporting crowded plates ● Reporting counts from multiple dilutions
Enumeration procedures
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
● staining properties● cell morphology● colony morphology● use of selective culturing● biochemical or other means of identification● genetic analysis
Characterization
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Validation of method for Validation of method for removing microorganismsremoving microorganisms
● Repetitive recovery
● Inoculating a known number of microorganisms onto product
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Repetitive recovery
Treatment no. Colonies 1 86 2 6 3 1
4 1Total 94
Removal by first treatment 80,8%Correction factor 1,24
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
●Sample size●Sampling frequency●Acceptable limits and actions taken
if a limit is exceeded●Trend analysis
Routine monitoring of bioburden
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
0
100
200
300
400
500
600
700
1 3 5 7 9 11 13 15 17 19 21 23 25 27
Endoscope no
Bio
bu
rden
(C
FU
)
Median:
0 CFU
Mean:
39 CFU
Bioburden in air/water channel of flexible endoscopes after disinfection
Ashurst L, Kjos B, Lingaas E. 2004
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Does bioburden determination tell the truth ??
Sampling deficiency?
Adhesion
Biofilm
Incomplete dispersion
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Does bioburden determination tell the truth ??
Lack of growth ?
Germination of spores
”Dormant” bacteria
Small colony variants
------
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Raw materials
Cleaning/lubrication/manufacturing liquid
Transport/holding containers
Work surfaces
Personell attire/hygiene practices
Handling/assembly
Packaging materials and procedures
Storage conditions
Characterization of organisms recovered
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Can the problem be solvedsimply by addinganother minute
to the sterilization cycle?
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Sykehushygiene 03/2002Universitetsklinikk
1.000.000
10.000
100
1
0.01
0.0001
0.000001
Num
bero
forg
anis
ms
Bioburden, inactivation factorand sterility assurance level (SAL)
SAL 10 -6
Exposure to inactivation process
: 1012
Inactivation required:
: 10 9 : 106
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
Dead microorganisms can also create problems EndotoxinProteinsTeichoic acid---
Sykehushygiene 05/2004Egil LingaasUniversitetsklinikk
● 0● 10● 100● 1000● 10000● 10.0000● 1.000.000● 10.000.000● 100.000.000
What is the maximum
allowable number of dead bacteria
on a sterile device?
?