WHAT’S IN THE FIELD: AN OVERVIEW OF FIRST
RESPONDER TECHNOLOGIES
by Christopher Chadwick, MS, specialist, public health preparedness and response
On a daily basis, suspicious packages and powders elicit a rapid response from law enforcement, fire fighters,
hazardous materials technicians and
Weapons of Mass Destruction Civil Support
Teams. These first responders rely on field
kits and devices to screen for the presence of
potentially harmful agents, such as anthrax
or ricin, in order to protect the public’s safety.
First responders use a variety of technologies
to screen samples in the field; however, these
technologies are not confirmatory and a
positive result does not necessarily indicate a
bioterrorism attack. The technologies do help
determine the initial steps of an investigation, including communications with public
health laboratories, members of the nation’s
Laboratory Response Network, for confirmatory testing.
non-specific assays
Some of the more common field tests are
non-specific assays that simply screen for
the presence of biological material (e.g., DNA,
proteins or ATP) in suspicious environmental samples, including liquids and powders.
While the presence of biothreat agents will
provide positive test results, so will the
presence of any bacteria if the amount falls
within a test’s limit of detection. Many of
these tests employ a simple process of adding
the sample, mixing it and reading the
results, which are typically available in as
little as five minutes. Fourier Transform
Infrared (FT-IR) spectroscopy is also a non-specific test that will match properties of a
sample to a variety of compounds in a library.
FT-IR systems are used primarily for screening samples for chemical threats and are
not generally recommended for screening
suspicious powders for biological materials.
Despite the ease of use, rapid results and low
cost, there are several details to consider
before using these assays in the field.
Because they are non-specific, positive
results are not indicative of a biological threat
when assessing suspicious packages or
powders. Additionally, the assays typically
have low sensitivity (how often the test will
correctly identify a positive) and specificity
(how often the test will correctly identify a
negative). Given these limitations, first
responders should only use these assays for
initial screening and follow up with more
specific tests.
Immunoassays
In contrast to the non-specific assays,
immunoassays aim to differentiate specific
biothreat agents in a sample. These assays
utilize a lateral flow assay format such that
the sample flows through a reagent zone
containing dye-labeled antibodies specific to
the various agents. If the antibodies bind to
the target agent, the antibody-agent complex
will be immobilized by secondary antibodies
in the capture zone, resulting in a visible line
on the test strip. There are a variety of assays
ranging from single-target to multi-target
tests capable of testing for Bacillus anthracis,
Yersinia pestis, Brucella species, Francisella
tularensis, botulinum toxin, ricin toxin and
staphylococcal enterotoxin B.
First responders utilize a handheld FT-IR spectrometer to screen
a suspicious environmental sample in the field. Photo courtesy of
Dana El-Hajjar, MBA, Nebraska Public Health Laboratory
Like the non-specific assays, immunoassays
are advantageous due to their ease of use,
rapid results and low cost, but because the
strips require liquid samples, a suspicious
powder would require the first responder to
have a collection kit that would solubilize the
sample. Due to the sensitivity of tests with
sample concentrations, a primary concern for
these assays is false negatives. Highly concentrated samples often result in the blocking of the secondary antibodies in the capture
zone. Thus, the antibody-agent complex for
a positive sample may not bind effectively,
leading to a false negative result on the test
strip. Also, further manipulation of threat
powders in the field is not recommended due
to the potential to aerosolize the sample.
PCr-Based systems
Although not as commonly used as non-
specific assays and immunoassays, hand-
held polymerase chain reaction (PCR)-based
systems are an emerging technology for field
screening by first responders. These systems
utilize disposable assays and reagents to
amplify DNA regions that are unique to a
panel of biothreat agents. Integrated optical
components will measure the DNA prod-
ucts—usually by fluorescence— and the
system’s output will indicate if a sample is
positive for any of the agents.
Although the actual systems are emerging,
the PCR technology is advanced and advantageous due to its high sensitivity and specificity. Manufacturers have made adjustments
to some of these systems to better accommodate the first responders’ needs (e.g.,
more rugged design, reduced weight, battery
power). In contrast to the other assays and
kits, PCR-based systems can be expensive
and require longer assay times. PCR inhibitors do pose a threat to results, but some
systems have integrated sample preparation
to remove the inhibitors while others will
instruct the user to dilute a sample to reduce
the effects of any inhibitors. Additionally, the
systems are not capable of detecting toxins,
unless there is an associated DNA component, as is with castor bean DNA in
the preparation of ricin toxin.
Due to the sensitive nature of the results of
all field technologies, first responders should
require that field screening kits and devices
be accurate and reliable and produce high-confidence results. The sensitivity and specificity of the technologies are very important:
false positives can lead to public panic and
inappropriate action and false negatives can
lead to life-threatening exposures and loss
of public trust. In its position statement, The
Need for a Quality Assurance Program for Kits and
Devices Used in the Field to Screen for Hazardous
Biological and Chemical Warfare Agents, 1 APHL
echoes these needs of the first responders
while also focusing on the need for an overall
quality assurance program to ensure first
responders have access to performance verification, field validation, proficiency testing,
training and annual competency assessment
for field screening technologies. It should be
noted that many of the technologies described above have not undergone comprehensive evaluation studies in the laboratory
and field. Existing partnerships among public
health laboratories and their first responders help address several of these needs and
ensure the public’s safety and health with the
timely reporting of high-confidence results
during potential emergencies. u
1. APHL. The Need for a Quality Assurance Program for Kits and
Devices Used in the Field to Screen for Hazardous Biological and
Chemical Warfare Agents. www.aphl.org/policy/positions/Pages/
default.aspx
