Webcast Transcript
CDC Responds: Coping with Bioterrorism—The Role of the Laboratorian
(November 9, 2001)
(View the webcast on the University of North Carolina School of Public Health site.)
Segment 6 of 9
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Ms. Rayam:
I would like to thank you all for your very timely and very
important information contributing to this very important discussion
on the effectiveness of the laboratory, safety precautions, and
testing. Dr. Tenover, I’d like to take this a step further with
yet another question that might spark some more discussion. How
is the CDC determining what antibiotics are effective for treating
these anthrax infections?
Dr. Tenover:
Lisa, it’s very important to note that there is no standard
method yet defined for Bacillus
anthracis testing. So here at CDC we’re using the reference
broth microdilution method as defined by the National Committee
for Clinical Laboratory Standards. So far, of the 15 clinical isolates
of anthrax that we tested from the U.S., all have been susceptible
to penicillin, doxycycline, and ciprofloxacin. At this time, however,
we are not recommending that other laboratories, including state
health departments, do this testing, and there’s really 3 reasons:
the first one is one of safety. It’s very important to recognize
that susceptibility testing potentially could produce aerosols.
So we do this testing in a Biosafety Level 3 laboratory in a biological
safety cabinet.
The second one is a scientific one. That is, we are still understanding
the ways that this organism can become resistant to antimicrobial
agents, and the optimal method for testing has not yet been determined.
So we hope to work out these procedures, and at that point we will
reconsider disseminating the methods to other laboratories.
The last one really is the practical issue, though, and that is
we have evaluated alternate methods of susceptibility testing that
potentially could be done within the safety cabinet. However, at
this point none of them reflect the methods and the results that
we get by the broth microdilution reference method. So right now,
again, that is the method we are using here at CDC.
It raises several other questions, though, that we’ve received during
the past week, and I’d like to share some of those with our panel.
Again, Tanja, let me start with you. We’ve had a lot of discussion
about typing, molecular subtyping of this organism. Can you comment
on the use of pulsed-field gel electrophoresis or ribotyping or
other molecular methods?
Dr. Popovic:
Certainly. I think we can all appreciate the importance
of the issue of molecular typing at this time, because that is the
approach that allows us quite frequently to trace the origin of
organisms in question. Let me start by saying that Bacillus
anthracis is extremely homogeneous. A number of methods, including
those that you have mentioned, have been tested and tried. Unfortunately,
it seems that all organisms—all
Bacillus anthracis organisms—when tested by these methods look either
identical or very much alike. So it does not appear to be a lot
of differentiation potential. As I have briefly mentioned, therefore,
currently the method of choice is multilocus VNTR typing approach,
in which we focus on a number of chromosomal and plasmid targets,
and we come out with a pattern that can then later be associated
with temporal or geographic or other relevant epidemiological markers,
and this method has been used again in a real-time manner throughout
this investigation, and we have found it to be extremely useful.
Dr. Tenover:
Good, thank you. Richard, in your presentation you mentioned
that some states have more than one Level B laboratory. So how do
we know which specimen to send to which laboratory?
Mr. Kellogg:
Well, yes; in general, most states have more than one B
level laboratory. For example, Texas (for Bacillus
anthracis) has eight. There are B level laboratories, though,
not only at the state level facilities, but also at large city and
county public health laboratories, and federal and military facilities
as well. By contacting your state public health laboratory director,
your closest B level facility can be identified in advance. Always
keep in mind that the designation, the rating is agent-specific.
Dr. Tenover:
Good, thank you. Michael, we received a lot of questions
from Level A laboratories about how do we disinfect our benches,
and do we need to do special autoclaving to get rid of these samples?
Can you comment about using bleach versus maybe a quaternary ammonium
compound for disinfecting lab surfaces?
Dr. Miller:
Sure. A lot of people are really concerned about how to
take care of their disinfectant issues here. We recommend a 10%
solution of household bleach, and that’s simply made by one part
bleach into 9 parts of water. This takes care of virtually all vegetative
cells. While it’s not by definition a sporicide, it actually reduces
the number of spores 3 to 5 logs. Now, quaternary ammonium compounds,
alcohol, other normal hospital disinfectants are not effective against
these spores, so we are recommending the 10% bleach solution.
Now, what about autoclaving? In our laboratories, we for our own
purposes use a one-hour autoclave time, but that’s because we have
large loads and large amounts of potential anthrax inside those
loads. But the clinical laboratory need not vary from the routine
15-minute autoclave time that they’re using now. That should adequately
kill the spores of Bacillus
anthracis.
Dr. Tenover:
Good, thank you. Tanja, in the news there’s been a lot about
hand-held devices for finding spores in the environment. Recently
we heard about a new PCR test from the Mayo Clinic. I wonder if
you could comment about these procedures?
Dr. Popovic:
Well, this is certainly not an unexpected question and I’ll
be happy to comment. I’d like to make a distinction between the
hand-held devices that are primarily used to detect spores of Bacillus
anthracis in the environment and those PCR-based tests that
are used to detect genetic material of Bacillus
anthracis, either directly,
in clinical specimens, or on the growing culture. Regarding
hand-held devices, CDC is not recommending use of these hand-held
devices for testing environmental samples. Data that is currently
available and provided by the manufacturers of these devices suggests
that the number of spores necessary for the test to be positive
is very large, and they go up to 10,000—in the range of 10,000. And while that
might be of value in heavily contaminated areas or samples, we might
actually miss areas where that level of contamination is not so
high. So CDC has been asked to assist in validation and evaluation
of these assays. As soon as the studies are underway and completed,
the results will be shared.
The second is the comment about the PCR assay such as that as reported
by the Mayo Clinic. I’d like to say, over the past 2 years, we have
worked with a number of partners and have developed a PCR-based
assay that has proven to be extremely sensitive and very specific
that has been used for the past 5 weeks intensively, primarily in
our Advanced Technology Laboratory that serves for that screening
purpose. And, specifically, about the Mayo Clinic assay: just like
any other new assay, it does need to be compared to the assays that
are already available, and until such tests are done, it is very
difficult to talk about specificity, sensitivity, and appropriateness
of a general use of these assays.
Dr. Tenover:
Good, thank you. Michael, maybe we can talk a little bit
about environmental sampling at the Level A laboratory level. What
are sort of the boundaries if the laboratory director is approached
by the hospital administrator and wants to have their mailroom cultured?
How would you advise these people, the laboratory directors?
Dr. Miller:
Well, the good point is that you’re approached by your own
management, and I believe if that’s the case, where you have been
asked to sample an area within your own hospital where there’s a
low risk or no risk, then probably it’s okay to provide this type
of sampling. And all this would mean would be using, again, a non-cotton
swab that has been moistened, rubbed over a specified area of a
tabletop or a mailbox or whatever you’re sampling within your institution,
taken to the laboratory and heat shocked in 1½ ml of saline, and
then plated. The heat shock takes place at 65°C for 30 minutes,
then you plate 100 microliters. That’s what we do. Now, I don’t
think at this point that hospitals at all should be taking on specimens
from which there really may be a credible threat, or we just don’t
want to bring into the hospital laboratory (or into the facility
where our patients are) specimens that may likely be contaminated
with anthrax spores. So if we’re going to do environmental sampling,
it probably needs to be done within the institution, and management
certainly needs to be involved in that decision.
Dr. Tenover:
Good, thank you. Our last question goes to you, Richard,
and that is sort of a follow-up to what Michael just said. What
problems would you see in performing Level B type of activities
in a Level A laboratory?
Dr. Kellogg:
Well, I really do want to reiterate what Mike has said,
and that for Bacillus anthracis, the LRN does not recommend
that clinical labs, especially those located in patient care facilities,
pursue LRN B level status and high-risk environmental sample testing.
The LRN has particular concerns about potentially high-risk environmental
samples, such as spore powders, especially those that could further
contaminate and cause contamination problems in a facility. Other
environmental samples not related to a credible threat assessment
or established area of exposure may be done at Level A labs. But
again, this should be very low-risk work, often taken to calm people’s
fears, and again, at the discretion of the laboratory management.
Dr. Tenover:
Good. Thank you all for your responses.
Ms. Rayam:
Again, thank all of you. Very timely responses during a very critical
time in America. Thanks to you all.
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