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Can I
get screened or tested to find out whether I have been exposed to anthrax?
There is no screening test for anthrax; there is no test that a doctor
can do for you that says you've been exposed to or carry it. The only
way exposure can be determined is through a public health investigation.
Nasal swabs and environmental tests, are not tests to determine whether
an individual should be treated. These kinds of tests are used only to
determine the extent of exposure in a given building or workplace.
If patients
are suspected of being exposed to anthrax, should they be quarantined
or should other family members be tested?
Direct person-to-person spread of anthrax is extremely unlikely and anthrax
is not contagious. Therefore, there is no need to quarantine individuals
suspected of being exposed to anthrax or to immunize or treat contacts
of persons ill with anthrax, such as household contacts, friends, or
coworkers, unless they also were also exposed to the same source of infection.
Does
CDC collect samples to test the bacteria?
CDC is engaging its partners in the Laboratory Response Network (LRN)
in states all across the United States. The LRN is a collaborative partnership
and multilevel system linking state and local public health laboratories
with advanced capacity laboratories --including clinical, military, veterinary,
agricultural, water, and food-testing laboratories -- to rapidly identify
threat agents, including anthrax. Local clinical laboratory testing is
confirmed at state and large metropolitan public health laboratories.
CDC conducts the definitive or highly specialized testing for major threat
agents. There are 100 laboratories in the network; none of them are commercial
labs.
When
an area is tested for the presence of Bacillus anthracis, how long
does it take to get the results?
Before testing can begin, samples must be collected in a form suitable
for testing. The length of time it takes to get test results depends on
both the kind of test to be performed and the laboratory’s workload.
Some tests may take only a short time to perform, but confirmation takes
longer. It may take many days to get the test results.
Testing
is a two-step process. The first test, a screening test, may be positive
within 2 hours if the sample is large and contains a lot of Bacillus
anthracis, the organism that causes the disease anthrax. However,
a positive reading on this first test must be confirmed with a second,
more accurate test. This confirmation test, conducted by a more sophisticated
laboratory, takes much longer. The length of time needed depends in part
on how fast the bacteria grow, but results are usually available 1 to
3 days after the sample is received in the laboratory.
Does
CDC recommend the use of home test kits for anthrax?
Hand-held assays (sometimes referred to as “Smart Tickets”)
are sold commercially for the rapid detection of Bacillus anthracis.
These assays are intended only for the screening of environmental samples.
First responder and law enforcement communities are using these as instant
screening devices and should forward any positive samples to authorities
for more sensitive and specialized confirmatory testing. The results of
these assays should not be used to make decisions about patient management
or prophylaxis. The utility and validity of these assays are unknown.
At this
time, CDC does not have enough scientific data to recommend the use of
these assays. The analytical sensitivity of these assays is limited by
the technology, and data provided by manufacturers indicate that a minimum
of 10,000 spores is required to generate a positive signal. This number
of spores would suggest a heavy contamination of the area (sample). Therefore
a negative result does not rule out a lower level of contamination. Data
collected from field use also indicate specificity problems with some
of these assays. Some positive results have been obtained with spores
of the non-anthrax Bacillus bacteria that may be found in the environment.
For these
reasons, CDC has been asked to evaluate the sensitivity and specificity
of the commercially available, rapid, hand-held assays for B. anthracis.
When this study is completed, results will be made available. Conclusions
from this study are not expected in the near future.
Is a
nasal swab test an approved diagnostic tool for determining whether a
person has been exposed to anthrax?
No. At present, CDC does not recommend the use of nasal swab testing on
a routine basis to determine whether a person has been exposed to B.
anthracis or as a diagnostic tool. At best, a positive result may
be interpreted only to indicate exposure; a negative result does not exclude
the possibility of exposure. Nasal swab screening may be used by public
health officials to assist in an epidemiological investigation of potentially
exposed persons to evaluate the dispersion of spores. See also http://www.bt.cdc.gov/documentsapp/faqanthrax.asp#Q602.
Are health
department laboratories capable of conducting testing?
All state health departments are capable of obtaining results of tests
on suspected infectious agents. Laboratories are usually classified as
Level A, B, C, or D. Level A laboratories are those typically found in
community hospitals, and these laboratories should be able to perform
initial testing on all clinical specimens (usually blood or some other
body fluid). Public health laboratories are usually Level B; these laboratories
are valuable for confirming or refuting preliminary test results and can
usually perform antimicrobial susceptibility tests on bacteria and viruses.
Level C laboratories, which are reference facilities and can be public
health laboratories, can perform more rapid identification tests. Level
D laboratories are designed to perform the most sophisticated tests and
are located in federal facilities such as CDC. Every state has a Laboratory
Response Network (LRN) contact. The LRN links state and local public health
laboratories with advanced-capacity laboratories, including clinical,
military, veterinary, agricultural, water, and food-testing laboratories.
Laboratorians should contact their state public health laboratory to identify
their local LRN representative. CDC’s
public bioterrorism Web site provides access to CDC’s Centers
for Public Health Preparedness, a national network of academic institutions
and local health departments whose goal is to ensure that local public
health workers are fully prepared to respond to current and emerging health
threats, including bioterrorism.
How effective
and reliable are anthrax tests?
There are many kinds of tests, and the reliability of each has not been
determined. In general, findings from culturing environmental samples
are specific; that is, a positive result reflects the true presence of
Bacillus anthracis, and a negative result likely means that no
B. anthracis is present.
What
is subtyping?
Subtyping is a laboratory process to identify different subtypes of organisms,
which is not possible with standard microbiological testing. Most Bacillus
anthracis subtyping is done by examining the organism’s molecular
structure for certain genetic characteristics that can then be compared
with those of other B. anthracis organisms to determine whether
they are the same or different. Differences between these two organisms
would indicate different strains.
Is subtyping
different from polymerase chain reaction (PCR)?
Polymerase chain reaction (PCR) is a laboratory method used to detect
and amplify genetic material from organisms. It can be used to diagnose
disease by identifying genetic material (DNA) commonly found in all Bacillus
anthracis strains or it can be used to subtype the organism by amplifying
specific genetic material and comparing it with known strains of B.
anthracis to see if it matches or if it is different. When PCR is
used for subtyping, the amplified genetic material is usually further
analyzed by other molecular methods, such as DNA sequencing.
What
method does CDC use to subtype Bacillus anthracis?
CDC uses a method called MLVA, which is the acronym for multi-locus
variable-number of tandem (consecutive) repeat analysis.
How does
MLVA (multi-locus variable-number of tandem [consecutive] repeat analysis)
identify different strains of anthrax?
MLVA examines a number of DNA segments within the chromosome or plasmids
of Bacillus anthracis that have specific repeat patterns of nucleotides
(fundamental DNA units). These repeats may differ by sequence and length,
as well as the number of times that they are repeated. Different types
of these repeats and the number of times that they are repeated provide
a specific pattern that will identify different strains of the organism.
More than 100 different strains of B. anthracis have been identified
using this method.
When
is environmental sampling performed?
Environmental sampling is the sampling of the air, soil, dust, water,
and physical surfaces to identify the presence or absence of bacteria,
chemicals, and radiological materials (see “Procedures for Collecting
Surface Environmental Samples for Culturing Bacillus anthracis“).
In the case of anthrax, this is used to identify its location and presence
in the environment. Environmental sampling would be conducted if there
were a threat or possibility of Bacillus anthracis contamination.
However, the presence of B. anthracis in an environmental sample
does not mean the person will get the disease.
Why is
environmental sampling performed?
- To identify
the site or source of B. anthracis that could lead to exposure
and disease,
- To trace
the route of an exposure (e.g., a letter),
- To guide
clean-up efforts in a facility with known exposure, and
- To assess
biosafety procedures in laboratories processing anthrax specimens.
What
is a nasal swab test?
A nasal swab involves placing a swab inside the nostrils and taking a
culture. The CDC and the U.S. Department of Health and Human Services
do not recommend the use of nasal swab testing by clinicians to determine
whether a person has been exposed to Bacillus anthracis, the bacteria
responsible for anthrax, or as a means of diagnosing anthrax. At best,
a positive result may be interpreted only to indicate exposure; a negative
result does not exclude the possibility of exposure. Also, the presence
of spores in the nose does not mean that the person has inhalational
anthrax. The nose naturally filters out many things that a person breathes,
including bacterial spores. To have inhalational anthrax, a person must
have the bacteria deep in the lungs, and also have symptoms of the disease.
Another
reason not to use nasal swabs is that most hospital laboratories cannot
fully identify anthrax spores from nasal swabs. They are able to tell
only that bacteria that resemble anthrax bacteria are present.
What
is the turnaround time for an anthrax test of an environmental sample?
Before testing can begin, samples must be collected and arrive in a form
suitable for testing. The length of time necessary to get results of tests
depends on transportation to the laboratory and the specific tests to
be done. Testing is a two-step process. Initial screening tests (such
as Gram stain) may be positive within two hours if the sample is large
and the concentration of bacteria is high. These tests are used to narrow
the definition of the sample. The confirmation tests take much longer,
depending in part on how fast the bacteria grow, but are usually available
24-48 hours after the sample is received by the laboratory. (See “Basic
Laboratory Protocols for the Presumptive Identification of Bacillus
anthracis".)
Is the
Mayo Clinic/Roche Rapid Anthrax Test a new test?
This is not a “new test.” The Laboratory Response Network (LRN) has been
using a validated real-time polymerase chain reaction (PCR) assay on the
LightCycler for some time. CDC has also developed and validated real-time
PCR assays for Bacillus anthracis for the SmartCycler™, ABI/PE
7700 and 5700. In addition, Idaho Technology has a real-time PCR assay
for B. anthracis that can be used with the R.A.P.I.D.™, which is
similar to the LightCycler™. SmartCycler is a trade name of Cepheid; R.A.P.I.D.
is a trade name of Idaho Technology; LightCycler is a trade name of Roche;
Idaho Technology is the name of a company.
Is the
Mayo Clinic assay the same as the assay available to Laboratory Response
Network (LRN) laboratories?
No. The Mayo Clinic assay targets the Lethal Factor (lef) gene
on the virulence plasmid p0X1 and the Protective Antigen gene (pag)
on p0X2. This assay has been tested with DNA from 32 strains of Bacillus
anthracis, 26 Bacillus species, and 21 different bacterial
genera commonly encountered in human specimens. The Mayo Clinic assay
has not been validated in multiple laboratories.
The CDC
assay uses targets on p0X1, p0X2, and the chromosome. A total of 100 Bacillus
anthracis isolates were used to evaluate the sensitivity of the assay.
Of the 100, 77 were selected to provide the best possible representation
with respect to geographic origin and date isolated. The strains were
obtained from infected animals, humans, and from industrial sites associated
with anthrax outbreaks; they span 58 years (1939-1997) and are from various
countries. In addition, five p0X1-cured strains (including the Sterne
strain) and one p0X2-cured strain (Pasteur strain) were included. For
evaluation of the specificity of the assay, 54 Bacillus species
were used (B. subtilis, 9; B. cereus, 23; B. thuringiensis,
12; and B. megaterium, 10) as well as 250 other DNAs of various
viruses and bacteria from human, animal, and insect sources. The assay
was validated in a multicenter study by using state public health laboratories
that had the specific platform.
What
are the limitations of the Mayo Clinic test?
Because the Mayo Clinic assay uses only two plasmid targets, it cannot
identify Bacillus anthracis strains such as Sterne or Pasteur that
may be present in environmental specimens. This would not be a problem
if the assay were used to confirm the identity of a gram-positive, non-motile,
non-hemolytic rod.
Is CDC
going to validate this assay?
CDC is testing samples from the current anthrax outbreak. When we have
sufficient time, we will study this and other anthrax assays.
Are we
aware of any sensitivity or specificity issues with the Mayo Clinic test?
Should we expect a large number of false positive/negative results?
On the basis of the data provided by the Mayo Clinic, the assay appears
to be sensitive and specific. However, the results are only as good as
the method used to prepare the sample for analysis. There have been no
data provided to indicate the types of samples that can be assayed or
how they are to be processed. The Food and Drug Administration (FDA) has
not seen the package insert for this test. The CDC assay has been validated
for different types of samples and sample processing methods.
Are we
furnishing CDC-tested equipment and reagents to laboratories?
Through the bioterrorism cooperative agreement, CDC has funded the purchase
of platforms for real-time polymerase chain reaction (PCR) assays for
the Laboratory Response Network (LRN). To date, 61 instruments have been
purchased or ordered. Among these are 17 LightCyclers,™ 23 SmartCyclers™,
13 7700s, and 5 5700s. Reagents for real-time anthrax assays are made
at CDC and placed in inventory. They are available at no charge to LRN
laboratories. Currently, reagents for the LightCycler™ anthrax assay are
available; reagents for the other platforms will be available soon. All
of the assays have undergone the same rigorous validation procedure.
If a
laboratory asks our opinion on whether to use Mayo Clinic/Roche Rapid
test, what is our answer?
The Food and Drug Administration (FDA) considers this an investigational
assay. As such it should be used only in conjunction with other tests,
such as culture tests. Currently, polymerase chain reaction (PCR) assays
are not considered confirmatory assays.
Will
CDC accept results from laboratories that use this assay?
Currently, polymerase chain reaction (PCR) assays are not considered confirmatory
tests for anthrax. PCR-positive specimens (or cultures) should be forwarded
to the nearest LRN laboratory for confirmation.
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