Investigating
Sterilizer Test Failures
By Charles A. Hughes
What does a facility do when faced with a “positive” spore
test after monitoring their sterilizer? According to the CDC (Center
for Disease Control and Prevention) guidelines… “If spores
are not killed in routine spore tests, the sterilizer should immediately
be checked for proper use and function and the spore test repeated. If
the spore tests remain positive, use of the sterilizer should be discontinued
until it is serviced”.
Now that private-offices and clinics are spore testing sterilizers as
recommended and/or required by local, state and federal agencies; more
and more questions are being asked regarding the proper use and function
of sterilization equipment. The spore test itself is sometimes even questioned
along with the person or Lab culturing the test to see if it grows (Positive
= Non Sterile) or does not grow (Negative = Sterile). Let’s review
each of these questions as they are related to possible sterilizer failure.
STERILIZER
FUNCTION
Depending on the type of sterilizer, it will function differently from
other types used to process instruments and materials. For example, a
Steam sterilizer functions differently than a Chemical vapor, which functions
differently from a Dry heat sterilizer. What type(s) of sterilizers do
your facilities use? All users must know the sterilizer type, as operation,
packaging materials, loading instructions and even the spore test are
all specific to the type of sterilizer being used.
Steam sterilizers commonly
operate at 250F/121C for 30 minutes or 270-273F/132-134C
for 10 minutes. These are exposure times only and
do not include temperature come up, come down or
dry times. Special Note: Proper drying of wrapped
loads is critical in order to maintain sterility
until point of use. At 250F,
pressure should read between 15-18 psi and 30-32
psi at 273F. If your sterilizer times, temperatures
or pressure readings vary from these, be sure to
check the Operator/Service Manual to verify you
are running an approved cycle. Users who do not
have an Operator/Service Manual should contact
the sterilizer manufacturer for a replacement.
Steam sterilizers require distilled water and all
manufacturers warn against using tap water as it
can damage the sterilizer and reduce the quality
of the steam, which can cause sterilizer failure.
In addition, door gaskets should be cleaned daily
and repaired or replaced as needed. A poor door
seal, clogged air trap jet, blocked safety valve
and/or inadequate water fill levels can all cause
a steam sterilizer to fail. Steam sterilizers should
be tested at least weekly with Bacillus stearothermophilus spores
that are commercially available in paper strip,
self-contained vials or sealed glass ampoule formats.
Chemical vapor sterilizers operate
at 270F/132C for 20 minutes with no dry time. Newer
units also have a 7-minute FLASH cycle, but is
limited to “single, unwrapped instruments” only.
This type of sterilizer does not use distilled
water, but rather a proprietary solution (alcohol/formaldehyde)
available from the manufacturer (Barnstead/Thermolyne,
formerly MDT Corp.). It is important that the sterilizer
dispense the proper amount of solution during each
cycle, because 270F/132C for 20 minutes with heat
only, is not enough to kill spores. Again, door
seals must be secure, traps must be cleaned and
the solution must be viable (shelf-life = 24 months).
Chemical vapor type sterilizers should be tested
at least weekly with Bacillus stearothermophilus spores,
but only in the paper strip format.
Dry heat sterilizers are
available in convection and rapid heat transfer
designs with drastically different cycle parameters.
For example, traditional convection type sterilizers
should be operated at 320F for 1-2 hours depending
on load size. The Cox Rapid Heat Transfer type
sterilizer available from Alfa Medical operates
at 375F with preset cycles of 6, 8 and 12 minutes.
Dry heat sterilizers only require electricity to
operate and depending on the manufacturer, some
units run on 110V and some require 220V. Convection
and Rapid Heat Transfer dry heat sterilizers should
be tested at least weekly with Bacillus subtilis
spores, but only in the paper strip format.
OPERATOR
ERROR
Selecting the correct cycle conditions, packaging materials and spore
tests are the responsibility of the Operator. For example, running an “unwrapped” cycle
with a “wrapped” load will cause sterilization failure, as
will using the wrong packaging materials with the correct cycle. Be sure
your facilities know how to select cycle conditions and proper packaging
materials. Overloading is another reason why sterilizers fail, as the
recommended cycle time is not enough to compensate for the load size.
New sterilizers are now required to submit maximum load testing to the
FDA when applying for approval, showing they have compensated for large
loads; however, older sterilizers usually have not. Users should limit
the size of their loads or add additional time to compensate for large
loads per the manufacturers instructions. Chemical vapor type sterilizers
and convection type dry heat sterilizers have been found to be especially
load sensitive.
Operating a sterilizer from a COLD START can also cause sterilizers to
fail and therefore, as many manufacturers now recommend running a warm
up cycle first, in order to preheat the sterilizer; while other manufactures
tell you to add a specific amount of exposure time to their standard
cycle when running from a COLD START. Once again, be sure to check the
Operator/Service Manual from the manufacturer.
SPORE
TESTS and TESTING LABS
Since most chemical indicators turn color by heat only, spore testing
is considered the best way to document all parameters for sterilization
(time, temperature & sterilant contact) have been achieved.44 Distributors
who sell spore tests are not required to be FDA registered as they typically
do not re-package or re-label them. Testing labs; however, usually do
and therefore, they must be FDA registered and meet strict QSR (Quality
Systems Regulations) guidelines. Lab technicians who are not careful
can contaminate the spore test during transfer and culturing, especially
with Bacillus subtilis spores, which are incubated at 35-37C. When selection
a Testing Lab for 3rd party verification, be sure they are experienced
(i.e. gram stain all positives to verify spore growth and not Lab error
prior to reporting that your test has failed), are FDA registered and
can document that their spore test is approved for your specific type
of sterilizer!
References:
- CDC
Guideline for Handwashing & Hospital Environmental
Control, Biological Monitoring of Sterilizers, 1985.
- OSHA
Technical Notes, #23, March 1, 1990.
- Hughes,
C., Surgical Services Management: Sterility is Event
Related, Not Time Related. Vo. 2, No. 10, October
1996.
- JADA,
Biological Indicators for Verifying Sterilization.
Vol 117, October 1988.
About
the author…
Charles is the General Manager of SPSmedical
Supply Corp. located in Rochester, NY. SPSmedical
is the largest sterilizer testing laboratory in N.
America and the company develops, manufactures and
markets a full line of sterility assurance products.
Certified as a Health Education teacher, Charles
has worked for over 15 years in the manufacturing
industry in areas of R&D, Regulatory Affairs,
Microbiology, Marketing and Sterilization Training.
A member of AAMI, IHSCMM, ASHSCP and OSAP, Charles
has extensive lecturing experience, including presentations
to sterilizer and instrument manufacturers, OR departments,
Dental organizations, and CS organizations throughout
the U.S. and Canada. You may contact the author @
(800) 722-1529 or E-mail: chughes@spsmedical.com
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