Epidemiology and the PulseNet
Lets begin with a little
background on this subject... Molecular epidemiology is a science that combines the
field of molecular biology with traditional epidemiologic research. Molecular
biology refers to the study of the molecules that are building blocks associated
with living organisms. The two types of molecules that molecular biology studies are proteins
and nucleic acids. The two nucleic acids are known as deoxyribonucleic acid
or DNA, and ribonucleic acid or RNA. The genetic information of each
living organism is carried in either their DNA (for every living thing except for some
viruses), or their RNA (for some viruses only).
Each human has a unique DNA sequence (with the exception of identical
siblings) that is the result of a combination of their mothers and fathers DNA
sequences. While bacteria also carry their genetic information in DNA sequences, there is
no combination of these sequences during normal reproduction. One bacterium simply divides
into two bacteria. So, unless there is a mutation or another alteration in the genetic
sequence, bacteria that descend from a single bacterium (known as a clone) will all
have identical DNA sequences. Even after a few generations of growth, bacteria with a
common single ancestor will have similar, if not identical, DNA sequences.
Pulsed-field gel electrophoresis (PFGE) is a technique used to
produce the DNA fingerprints from these DNA sequences. DNA fingerprinting by PFGE
involves isolating a DNA sequence from an organism, cutting it into pieces, and then
measuring the number and size of the pieces. The pieces are separated by running them
through a gel, which functions as a sieve. Smaller pieces go through quickly, while larger
pieces travel more slowly. The resulting pattern of bands, which looks like a bar code, is
the DNA fingerprint.
Prior to the introduction of PFGE, we could identify bacteria by name
(e.g., Salmonella or Shigella), and, in some instances, by other
characteristics (e.g., antibiotic resistance patterns or serotypes) to help us determine
if bacteria were related to one another. We are now able to determine much more precisely
how closely related bacteria are to one another by comparing their DNA fingerprints.
Identical or very similar DNA fingerprint patterns strongly suggest a close relationship,
while bacteria with distinctly different patterns are not closely related.
What is PulseNet? PulseNet is a national computer network of
public health laboratories. (Utahs Public Health Laboratory is one of 22 state
public health laboratories currently participating in the PulseNet.) These laboratories
use PFGE to obtain DNA fingerprints of bacteria that are believed to be associated with
foodborne illnesses. Once a DNA fingerprint is identified by a laboratory in the PulseNet,
it is loaded into the computer network. This network allows laboratories to compare their
DNA fingerprints with those that have been isolated from other PulseNet sites throughout
the country. In a short time after submitting the DNA fingerprint to the network, the
laboratory is notified whether or not there is a match for it in PulseNet. The pattern is
also stored for three months in the network so that it may be compared to fingerprints
that may be subsequently submitted. PulseNet contains DNA fingerprints of Escherichia
coli O157:H7 isolates now. There are plans to add DNA fingerprints of Salmonella
This new system should permit public health experts to identify
foodborne outbreaks associated with a common source rapidly and accurately. This computer
network provides a nationwide database of DNA fingerprints that can be searched within
hours. A mechanism to share such complex data at this speed has never existed before. An
additional strength of this new system is that it requires participating laboratories to
use the same procedures to identify DNA fingerprints. In the past, all laboratories did
not use the same procedures, and this made the comparison of DNA fingerprints between
laboratories difficult or impossible.
Why is PulseNet necessary? When people think of foodborne
outbreaks, the classic bad potato salad at the church supper scenario often
comes to mind. Obviously, the advanced technology behind PulseNet may not be nearly as
important as old-fashioned epidemiology in this kind of situation. With changing food
distribution patterns, however, foods may be distributed to multiple states or even
multiple countries before bacterial contamination is detected. For example, two recent
recalls involved tons of ground beef possibly contaminated with E. coli O157:H7
that had been purchased by consumers throughout the United States. PulseNet allows public
health experts to compare the DNA fingerprints of bacteria from widely dispersed locations
so they can determine if the bacteria are related to each other (and may be from a common
exposure). The DNA fingerprints from patient specimens can also be compared to the DNA
fingerprints obtained directly from the implicated food itself.
How can I learn more about PulseNet? You could visit the CDC on
the Internet at www.cdc.gov/ and enter PulseNet on the CDC web search for more details
about PulseNet. You may also contact your local health department or the Utah Department
of Health to learn more about foodborne disease surveillance.
Promotes Safer Use of Insect Repellent DEET
New labeling requirements to ensure the safe use of insect repellents containing
DEET (N,N-diethyl-meta-toluamide) have been issued by the EPAs Office of Pesticide
Programs. The EPA is issuing the new labeling requirement as a result of a comprehensive
review of the most recent health and safety data available on DEET, the active ingredient
most widely used in insect repe- llents.
About one-third of the US population uses a product containing DEET
annually. If DEET is used as directed, it will not pose significant health risks to
consumers. However, the EPA is requiring changes to current labels to ensure that DEET is
applied safely, particularly on children. New labels will direct parents to not allow
children to handle this product. The product should not be used near eyes and mouths of
young children, and should be washed off after returning indoors. More information on DEET
and the use of this product and other insect repellents is available at: http://www.epa.gov.
Once you have the EPA Homepage, search in pesticides, DEET. You can also call EPAs
Communication Services Branch at 703-305-5017. (Source: EPA Press Release April 24, 1998).
How to use DEET products
Consumers can reduce their own risks when using DEET by
reading and following product labels. Statements on all DEET product labels will be
revised to include the following directions:
- Read and follow all directions and precautions on the product label.
- Do not apply over cuts, wounds, or irritated skin.
- Do not apply to hands or near eyes and mouth of young children.
- Do not allow young children to apply this product.
- Use just enough repellent to cover exposed skin and/or clothing.
- Do not use under clothing.
- Avoid over-application of this product.
- After returning indoors, wash treated skin with soap and water.
- Wash treated clothing before wearing it again.
- Use of this product may cause skin reactions in rare cases.
The following additional statements will appear on the labels of all aerosol and pump
spray formulation labels:
- Do not spray in enclosed areas.
- To apply to face, spray on hands first and then rub on face. Do not spraydirectly onto
1997 - 1998 Influenza Season in Utah
The intensity of the 1997-1998 influenza season peaked in the latter part of
December and the first part of January (see chart). Laboratories and physicians reported a
total of 50 laboratory confirmed cases to the Utah Department of Health, with the last
case reported during the first week in April. The second variable measured was the
percentage of children absent from school for the previous week. Every health district in
the state contributed weekly numbers by contacting school districts in their boundaries.
In the past, selected physician offices have been contacted weekly to
collect numbers of influenza-like illness seen during the previous week. This year the
Centers for Disease Control and Prevention wanted to expand the physician-based
surveillance of influenza-like illnesses. To do this, a toll-free number was provided, and
each week the physicians, or someone in their office, would dial up and provide numbers
for the previous week. Initially, Utah had nearly a dozen physicians who agreed to
participate in the physician based surveillance. Unfortunately, the physician based
surveillance did not work as expected and participation waned as the season progressed.
Consequently, we may be going back to weekly calls to selected offices.
In summary, Utah experienced a mild influenza season. Unlike last year,
there was no influenza type B isolated in the state during this season.
Report of Diseases of Low Frequency
Year-to-Date January 1 - June 30, 1998
(including a comparison for same time period 1994 -1997)
Utah Department of
Health, Bureau of Epidemiology
Monthly Morbidity Summary - June
1998 - Provisional Data
The Epidemiology Newsletter is published monthly by the
Utah Department of Health, Division of Epidemiology and Laboratory Services, Bureau of
Epidemiology, to disseminate epidemiologic information to the health care professional and
the general public.
Send comments to:
The Bureau of Epidemiology
Salt Lake City, UT 84114-2104
or call (801) 538-6191
Approval 8000008: Appropriation 3705
Rod Betit, Executive Director Utah Department of Health
Charles Brokopp, Dr.P.H. Division of Epidemiology and Laboratory Services
Craig R Nichols, MPA, Editor, State Epidemiologist, Director Bureau of Epidemiology
Cristie Chesler, BA Managing Editor