Determination of the efficacy of sterile

barrier systems against microbial

challenges during transport and storage

Hartmut Dunkelberg and Ulrich Schmelz

Medical 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, 2010

Sao 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)

0,000001

0,0001

0,01

1

100

10000

1000000

0 2 4 6 8 10 12 14 16 18 20

Exposure time (min)

Nu

mb

er

of

co

lon

y f

orm

ing

un

its (

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 changes

to 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

2:2

1

09:5

3:5

4

10:0

5:2

7

10:1

7:0

0

10:2

8:3

3

10:4

0:0

6

10:5

1:3

9

11:0

3:1

2

11:1

4:4

5

11:2

6:1

8

11:3

7:5

1

11:4

9:2

4

12:0

0:5

7

12:1

2:3

0

12:2

4:0

3

12:3

5:3

6

12:4

7:0

9

12:5

8:4

2

13:1

0:1

5

13:2

1:4

8

13:3

3:2

1

13:4

4:5

4

13:5

6:2

7

14:0

8:0

0

14:1

9:3

3

14:3

1:0

6

Time

hP

a

Humidity

0

20

40

60

80

09

:36

:40

09

:48

:20

10

:00

:00

10

:11

:40

10

:23

:20

10

:35

:00

10

:46

:40

10

:58

:20

11

:10

:00

11

:21

:40

11

:33

:20

11

:45

:00

11

:56

:40

12

:08

:20

12

:20

:00

12

:31

:40

12

:43

:20

12

:55

:00

13

:06

:40

13

:18

:20

13

:30

:00

13

:41

:40

13

:53

:20

14

:05

:00

14

:16

:40

14

:28

:20

Time

%

8

35

80

020

4060

80100

120

2,600 cm³ 5,300 cm³ 7,900 cm³

Packaging volume

nu

mb

er

of

mic

roo

rga

nis

ms

(CF

U)

pe

r p

ac

ka

ge

± Standard error

Microbial barrier efficiency of double wrapped

baskets

Determination of the efficacy of the sterile

barrier systemN0 = Number of bacteria in the air volume passing

the 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

4,814,53 4,27

0

1

2

3

4

5

6

2,600 cm³ 5,300 cm³ 7,900 cm³

Packaging volume

LR

V

± 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

4,814,53 4,27

0

1

2

3

4

5

6

2,600 cm³ 5,300 cm³ 7,900 cm³

Packaging volume

LR

V

± 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

99,9

9999

99,9

9990

99,9

9900

99,9

9000

99,9

0000

99,0

0000

90,0

0000

0,00

000

Required filtration efficiency (%)

Mic

rob

ial c

ha

lle

ng

e

SAL ≤ 10-6

Relationship between the airborne microbial challenge

and the required filtration efficiency for the assessment

of sterility

Airborne microbial

barrier efficiency is

printed 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

Filtration

efficiency in %

www.microbial-evaluation-of-sterile-barrier-systems.com/

0,22

1,52,2

63,951,7

164,8

0,1

1

10

100

1000

0 20 40 60 80

Atmospheric pressure changes (hPa)

Me

an

co

lon

y f

orm

ing

un

its

(CF

U)

pe

r p

ac

ka

ge

Microbial 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

Nu

mb

er

of

Sam

ple

s

< 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!