The Disease
Salmonella typhimurium DT104 causes a zoonotic food-borne
disease. It can be particularly severe in humans, affecting
the gastrointestinal tract and some times causing septicemia,
which can result in death. In most healthy individuals however,
S. t. DT104 infections are mild and self-limited.
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Foodborne transmission of S. t. DT104 has been documented
in several outbreaks. Suspected vehicles for transmission
of the organism included roast beef, ham pork sausage, salami
sticks, "cooked meats", chicken leg, and unpasteurized milk.
Analyses of 786 samples of fresh and frozen sausages in England
in 1994 demonstrated that 17% were contaminated with Salmonella
spp., including S.t. DT104. This indicates that these bacteria
are commonly present in some types of meats and pose a significant
risk if such foods are not cooked and handled properly. More
recently, disease in household pets has been linked to dried
"pigs ears" used as doggie treats. Animals infected with S.t.
DT104 have diarrhea and can carry this organism up to several
months after recovery. Farm families caring for sick farm
animals or people caring for sick pets can acquire the infection.
People can also acquire illness from exposure to other sick
people.
Following ingestion, the organism travels across the gastric
acid barrier and gains access to the small intestine, invading
the cells of the intestinal mucosa, and damaging them. Inside
the intestinal cell, the bacteria grow and multiply, spreading
to the other cells. They may colonize the intestine and can
enter the blood stream. Two or three days after ingestion,
symptoms associated with the intestinal invasion start: diarrhea,
abdominal cramps, nausea and vomiting and fever.
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Clinical signs of S.t. DT104 infection in humans may include
diarrhea, fever, headache, nausea, abdominal cramps, bloody
stools, and vomiting. In some cases, particularly in the very
young and in the elderly, dehydration can become severe and
life threatening. A study in the UK reported severe illness
including septicemia, which resulted in hospitalization among
41% of the patients and death in 3% of them. The symptoms
become evident 12 to 36 hours after ingestion of the contaminated
food and usually last for about 5 days. The duration and severity
of symptoms is dependent on host factors and the dose of the
bacteria ingested.
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S.t. DT104 is diagnosed by fecal testing. S. t. DT104 infection
should be considered in any patient with moderate to severe
gastroenteritis, especially if fever and headache are present.
Diagnosis may also be made though a positive blood culture.
Tests for identification of this organism include culturing
for Salmonella, serotyping of Salmonella isolates to determine
if they are typhimurium, phagetyping, and antibiograms to
determine the pattern of antibiotic resistance.
Other, more molecular-based diagnostic tools such as plasmid
profile analysis, pulsed field gel electrophoresis (PFGE),
and polymerase chain reaction (PCR), are also important in
identifying S.t. DT104. PCR which requires minute amounts
of DNA, has been used to subtype S. typhimurium isolates
in preliminary experiments and may prove to be vital in the
diagnosis of carrier individuals, both human and animal. Initial
reports indicate that these methods hold great potential for
fast , accurate diagnosis of S.t. DT104 in acute outbreaks
as well as in herd monitoring/screening programs. These molecular
tests are only available in reference laboratories.
S.t. DT104 infections in healthy persons are usually self-limited
and management consists of supportive medical care (fluid
and electrolyte replacement). Antibiotics are reserved for
treatment of severely ill persons who have systemic (septicemic)
disease.
The common antibiotics used for treating Salmonella infections
cannot be used for people infected with S.t. DT104 because
this strain is resistant to five commonly used antibiotics
(ampicillin, chloramphenicol, streptomycin, sulfonamides,
and tetracycline). Fluoroquinolones are the drugs of first
choice for bacteremia and serious intestinal infection. However,
recent reports from Denmark and UK have suggested increasing
resistance of S.t. DT104 to fluoroquinolones (ciprofloxacin)
related to the use of this antibiotic for the treatment of
Salmonellosis in farm animals. This will pose further problems
for treating this infection especially in patients with underlying
health problems.
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Although not all cases of S.t. DT104 infections are reported,
and precise information on the incidence is not available,
several countries have reported significant increases during
the last several years. The clinical features associated with
infection with S.t. DT104 may be more severe than other Salmonella
infections. In a study in the United Kingdom of 83 cases of
S.t. DT104 infection, 3% died, compared to a case-fatality
rate for non-typhoid Salmonella infections of approximately
0.1%.
In the U.S., infections caused by multi-resistant strains
of S. t DT104 were more likely to cause bacteremia and were
associated with longer hospitalization. In the UK, there was
a ten-fold increase in the number of human cases caused by
this multi-drug resistant strain over a six year period (1990-1996).
There has also been an increase in the number of isolates
with additional resistance to trimethoprim and ciprofloxacin.
These strains have been associated with hospitalization rates
twice that of other salmonella infections and with ten times
higher case-fatality rates. In a report from British Columbia,
Canada, it was shown that the highest incidence rate of case
persons with S.t. DT104 was in the 1-4 year old age group.
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