Determination of the efficacy of sterile barrier systems against microbial
challenges during transport and storage
Hartmut Dunkelberg and Ulrich SchmelzMedical Institute of General Hygiene and Environmental Health,
University of Goettingen, Germany
11th World Sterilization Congress and the 7th International Symposium of Sterilization and Hospital Infection Control,
July 30 – August 01, 2010Sao Paulo, Brazil
Theoretical probability of a non-sterile product ≤ 1 : 1,000,000
= Sterility Assurance Level (SAL) of 10-6 *
*CDC: Guideline for disinfection and sterilization in healthcare facilities, 2008
Sterile: state of being free from all living microorganisms
Microbial inactivation by steam sterilization (121°C)
0,0000010,0001
0,011
10010000
1000000
0 2 4 6 8 10 12 14 16 18 20
Exposure time (min)
Num
ber o
f col
ony
form
ing
units
(cfu
)D121°C-value*
SAL ≤ 10-6
*D-value= decimal reduction time
Sterilization procedures resulting in a product´s initial sterility
• Steam
• Ethylene oxide
• Formaldehyde steam
• Ionizing radiation
• Hydrogen peroxide gas plasma
Event-related factors limit shelf life
Impacts causing visible changesto the packaging:
- Cuts or breaks on gaskets,
- Punctures, tears,- Wetness, water stains,- Loosened locks and- Settled dust following
storage on open shelving.
Broken seals as a result of multiple handling
Dye penetration test
Impacts by air flow into the packaging during transport and storage challenge the filtration efficiency:
Transport to different heights above sea level,
Weather-influenced atmospheric pressure changes and Temperature variations.
Demonstration of gas permeability: Entering of gaseous bromine into the packaging
Event-related factors limit shelf life
Example of impact by challenging the filtration efficiency of the packaging
Air flow induced by cooling the packaging from 60 to 20 °C:
volume of the baskets: 2,600 cm³
381 cm³ of air entering the packaging.
Airborne microbial concentration in CSSD: 100 CFU/m³
Microbial challenge of the basket: 0.038 CFU
The confirmation of the product’s sterility at the point of use based on the SAL of 10-6
requires exact data about
the filtration efficiency of the packaging material and
the microbial challenge of the packaging during transport and storage.
Nebulizer
Impinger
Time control module
Vacuum pump
Exposure chamber method
Loading the packaging with nutrient agar
Atmospheric Pressure Changes
-20
0
20
40
60
80
09:4
2:21
09:5
3:54
10:0
5:27
10:1
7:00
10:2
8:33
10:4
0:06
10:5
1:39
11:0
3:12
11:1
4:45
11:2
6:18
11:3
7:51
11:4
9:24
12:0
0:57
12:1
2:30
12:2
4:03
12:3
5:36
12:4
7:09
12:5
8:42
13:1
0:15
13:2
1:48
13:3
3:21
13:4
4:54
13:5
6:27
14:0
8:00
14:1
9:33
14:3
1:06
Time
hPa
Humidity
0
20
40
60
80
09:3
6:40
09:4
8:20
10:0
0:00
10:1
1:40
10:2
3:20
10:3
5:00
10:4
6:40
10:5
8:20
11:1
0:00
11:2
1:40
11:3
3:20
11:4
5:00
11:5
6:40
12:0
8:20
12:2
0:00
12:3
1:40
12:4
3:20
12:5
5:00
13:0
6:40
13:1
8:20
13:3
0:00
13:4
1:40
13:5
3:20
14:0
5:00
14:1
6:40
14:2
8:20
Time
%
835
80
020406080
100120
2,600 cm³ 5,300 cm³ 7,900 cm³
Packaging volumenum
ber o
f mic
roor
gani
sms
(CFU
) per
pac
kage
± Standard error
Microbial barrier efficiency of double wrapped baskets
Determination of the efficacy of the sterile barrier system
N0 = Number of bacteria in the air volume passingthe porous packaging material during the test(= microbial challenge)
N1 = Number of bacteria registered on the plates in the packaging
Microbial barrier effectiveness in terms of the Logarithmic Reduction Value (LRV.):
N0
LRV = Log ---- N1
N1
Filtration efficiency (%) = [1 – ---- ] x 100 N0
4,81 4,53 4,27
0123456
2,600 cm³ 5,300 cm³ 7,900 cm³Packaging volum e
LRV
± Standard error
Filtration efficiency: 99.998 %
99.997 % 99.995 %
Logarithmic reduction value (LRV) of double wrapped baskets
1. Sterility assurance level ≤ 10-6
2. N0 = Microbial challenge during transport and storage
3. LRV = Microbial barrier efficiency of the packaging
Confirmation of the maintenance of sterility
Log N0 – LRV ≤ - 6
4,81 4,53 4,27
0123456
2,600 cm³ 5,300 cm³ 7,900 cm³Pack aging volum e
LRV
± Standard error
Assessment of maintenance of sterility. Example: 2,600 cm³-basket, cooling from 60 to 20 °C
Air flow : 381 cm³
Microbial challenge (N0) in the CSSD: 0.038 CFU Log 0.038 = - 1.42
Sterility is confirmed.
- 1.42 - 4.81 = - 6.23
0,0000010,00001
0,00010,001
0,010,1
110
99,99
999
99,99
990
99,99
900
99,99
000
99,90
000
99,00
000
90,00
000
0,000
00
Required filtration efficiency (%)
Mic
robi
al c
halle
nge
SAL ≤ 10-6
Relationship between the airborne microbial challenge and the required filtration efficiency for the assessment
of sterility
Airborne microbialbarrier efficiency isprinted on the package: LRV or % Filtration Efficiency
Assessment of maintenance of sterility in the healthcare setting
… … …
Assessment of maintenance of sterility in the
healthcare setting
Filtrationefficiency in %
www.microbial-evaluation-of-sterile-barrier-systems.com/
0,22
1,5 2,2
63,951,7164,8
0,1
1
10
100
1000
0 20 40 60 80
Atmospheric pressure changes (hPa)
Mea
n co
lony
form
ing
units
(C
FU) p
er p
acka
geMicrobial barrier efficiency of flexible
peel pouches
Microbial barrier efficiency of flexible peel pouches
1,4
1,92,1
1,6
1,2
1,5
0
1
2
3
0 10 20 30 40 50 60 70 80
Atmospheric pressure changes (n=21)
LR
V
Filtration efficiency 99,2 %
Mean filtration efficiency 93,7 %
Microbial barrier efficiency: 16 commercial porous medical packaging materials:
exposure chamber method*
0
2
4
6
8
Num
ber o
f Sa
mpl
es
< 1 % 1 - 10 % >10 %
% Maximal Spore Penetration
103/cm³ airborne bacterial spores; flow rate of 2 cm³ min-1 cm-1
*Data from: Sinclair CS, Tallentire A 2002 PDA J Pharm Sci Tech 56:11-19
Conclusion• The sterility of the packaging can be confirmed
at the SAL at the point of use. • This requires data on the microbial barrier
efficiency and information about the airborne microbial challenge during transport and storage.
• This stability program ensures the safety and the high quality of sterile supplies.
• The described concept of stability testing opens possibilities to optimize the packaging barrier properties by the modification of the design, the volume, and the method of packaging.
References• CDC: Guideline for disinfection and sterilization in healtcare
facilities, 2008; www.cdc.gov/ncidod/dhqp/pdf/guidelines/Disinfection_Nov_2008.pdf
• Food and Drug Administration. Guidance for industry – container and closure system integrity testing in lieu of sterility testing as a component of stability protocol for sterile products. Food and Drug Administration, Rockville, MD, February 2008. Available at: http://www.fda.gov/cber/guidlines.htm. Accessed: June 30, 2008.
• Sinclair CS, Tallentire A. Definition of a correlation between microbiological and physical particulate barrier performance for porous medical packaging materials. PDA J Pharm Sci And Tech 2002;56:11-19
Thank you for your attention!
