Central Sterile Services
Understanding Thermal Disinfection Using A0
What is A0?
A0 is an expression of the expended energy (time/temperature)needed for the disinfection process in a washer/disinfector to achievea desired level of kill. Another way to express this is “area-under-the-curve”– the amount of energy that was applied to a load.
Specifically, A0 is the time required to achieve a specified log reduction ofmicroorganisms based on the temperature of the thermal disinfection cycle.
The A0 concept is used mainly outside the United States and is described byEN (European Norm) ISO 15883. The number following the A0 symbol
represents the number of seconds needed at 80°C/176°F to achieve thelevel of disinfection specified by the particular A0 designation. According
to EN ISO 15883, the minimum disinfection requirement for human waste
containers is A0 60 and the mimumum disinfection requirement for surgicalinstruments is A0 600. No application for A0 3000 has yet been established.
Nevertheless, EN ISO 15883 specifies that a washer/disinfector must be
capable of achieving A0 3000.
Since the A0 represents a combination of time and temperature, there
are different ways to achieve specific levels of A0 disinfection. A0 600, forexample, may be achieved using the time and temperature combinations
seen below:

A0TEMP ºF/ºC

TIME
[SEC]
[MIN]

600

176/80600

10600

194/9060

1600

199/9330

0.5

Source: ISO 15883-1; annex B

References:
1.

Rosenberg U, Thermal Disinfection – The A0 Concept and the Biological Background, Central Service, Vol. 11, 2003

2. Rohm-Rodowald E, Jakimiak B, Chojecka A, Wiercinska O, Ziemba B, Kanclerski K, Recommendations for Thermal Disinfection Based on the Concept According toEN ISO 15883, Przegl Epidemiol, 2013;67:787-690
3. A0 Made Simple, STERIS Corporation 2008
4. Class II Special Controls Guidance Document: Medical Washers and Medical Washer-Disinfectors; Guidance for the Medical Device Industry and FDA Review Staff
http://www.fda.gov/RegulatoryInformation/Guidances/ucm073357.htm

One Integrated Approach to Healthcare.

What are the benefits of A0?
1.

Communication:		a. A0 refers to a specific disinfection level, regardless of which temperature was used or 						for how long.		b. The usage of A0 allows the direct comparison of disinfection levels
2. Time Savings:
Thermal disinfection begins to take place at 149° F (65° C) which is below the time/temperatureplateau for a typical washer/disinfector cycle. A0 takes the heating time during which thermal
disinfection is taking place into account. Often the A0 600 can be obtained shortly after reaching
the plateau.

Temperature C		a.									Time (Seconds)

NOTE: Countries using A0 continue to debate the benefits of A0 3000 or higher. The incremental gain inmicrobes killed going from A0 600 to A0 3000, depending on the specific organisms or strains, for example,
could easily be zero. As a result, a number of experts have argued that routine disinfection using A0 3000 is
not justified and that the time saved by using A0 600 versus A0 3000 can be put toward more cleaning andincreased throughput. In other words, A0 = 3000 is considered “doing-too-much” and it would be more usefulto spend the extra time required to achieve A0 3000 on cleaning instead.1, 2

What are the differences in requirements for thermal
disinfection in the United States versus Europe?

UNITED STATESEUROPE

FDA does not recognize A0, but does stipulatethat any washer/disinfector sold in the UnitedStates claiming thermal disinfection for reusable
medical devices must be capable of achieving
intermediate level disinfection.

Europe follows EN ISO 15883, which stipulates that:

Intermediate level disinfection is defined by FDA
as a 6 log reduction of a mixed suspension ofvegetative organisms and a 3 log reduction ofan appropriate thermophilic mycobacterium
species.3
All STERIS washer/disinfectors currently
being sold for disinfection of reusable medicaldevices meet or exceed FDA requirements forintermediate level disinfection and are
EN ISO 15883 compliant.

• A0 60 is a minimum requirement for human wastecontainers• A0 600 is a minimum requirement for disinfectionof surgical instruments.
• Washer/disinfectors must be capable of achieving
A0 3000, but does not define an application for
this.
National requirements can vary, but most hospitals
in Europe target disinfection above the minimum
requirement specified in EN ISO 15883 (e.g. BGA
or Bundesgesundheitsamt in Germany, now RKI,
specifies 93 °C/ 200°F for 10 minutes which would
yield A0 12,000)Summary: In the United States, the responsibility for ensuring compliance with thermal disinfection
requirements rests with the manufacturer. In Europe, the manager of the CSSD may decide in light ofprofessional advice, to program the washer/disinfector to perform the appropriate cycle on a given load.
FDA specifies a minimum log reduction requirement. Manufacturers must be able to produce
documentation to prove their equipment meets this requirement. EN ISO 15883 requires thermal mapping
documentation that a specific A0 value was achieved.

STERIS: Meeting and exceeding all accepted standards
and requirements globally
STERIS PLC is a global company and, as such, its washer/disinfectors comply with and exceed all
accepted standards and requirements for thermal disinfection worldwide. All STERIS washer/disinfector
cycles can be set to run using a time/temperature-based model (A0 600, 3000, 12000) if desired.
Regardless of a country’s specific thermal disinfection requirement, however, the unique efficacy profile
of STERIS washer/disinfectors delivers Customers the fastest cycle time of any washer/disinfectors
currently available.

Document # M4383EN.2016-11 Rev. A©STERIS Corporation. All Rights Reserved.