G.I. Tract Infections Student Copy - Page 1
MECHANISMS OF HUMAN DISEASE
MICRO CASE-BASED SMALL GROUP DISCUSSION
Session 13
G.I. TRACT INFECTIONS
Monday, January 22, 2001
9:30 A.M. - 11:30 A.M.
Reading Assignment:
Sherris Medical Microbiology, Chapter 20, pp. 321-338
Sherris Medical Microbiology, Chapter 21, pp. 345-352
G.I. Tract Infections Student Copy - Page 2
CASE HISTORY 1
A 26 year old woman comes to the traveler's clinic complaining of profound weakness and
severe diarrhea of one and one-half days' duration. She has just returned from Africa where she
worked for two months in a refugee camp on the border of Rwanda and Zaire. On the plane she
developed abdominal bloating, intestinal gurgling and nausea followed by two loose bowel
movements. Soon she was having profuse watery diarrhea occurring hourly. Stools were clear
and without odor.
You meet her in the clinic. She looks very weak but has no fever. Blood pressure is 94/60 lying
down and drops to 72/40 standing. She is admitted to the hospital. Admitting laboratory studies
include the following: .
Sodium
Potassium
Chloride
CO2
Fecal leukocytes
Fecal occult blood
138 meq/L
2.1 meq/L
95 meq/L
15 meq/L
None seen
Negative
1.
What is the mechanism of transmission of Vibrio cholerae?
2.
What host factors increase the likelihood of infection with V. cholerae?
3.
Describe the mechanism of action of cholera toxin.
4.
Besides toxin production, what other virulence determinant is essential for the
development of cholera?
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5.
How would you manage the dehydration? Why can oral rehydration fluid be used in many
cases of cholera?
6.
What advice would you provide to other travelers to Rwanda concerning avoidance of
cholera?
7.
List three public health solutions to the global problem of epidemic cholera.
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Case History 2
An 8 year old boy was admitted to the Pediatric Service with edema and high blood pressure. He
had been well until 8 days prior to admission when he developed severe abdominal pain, nausea,
vomiting and diarrhea. On the second day the diarrhea became bloody. The diarrhea continued
but had lessened in amount, remaining bloody. The mother did not report any fever. On
examination he appeared pale and had mild facial edema. Temperature was 37.6'C pulse 104 and
regular and the blood pressure was 140/95. His abdomen was tender. Chest x-ray was clear.
Abdominal x-ray disclosed edema of the transverse and descending colon with thumbprinting.
Laboratory studies included the following.
Hemoglobin
Peripheral smear
WBC
Platelet count
Creatinine
Lactic dehydrogenase
Fecal leukocytes
Stool culture
8.5 gm/dl
Schistocytes present
17.5x103/mm3
42,000/mm3
5.4 mg/dl
485 IU/ml
Absent
Sorbitol-negative
Escherichia coli
1.
What enteropathogenic type of Escherichia coli is causing this infection?
2.
What complication of E. coli enteritis did this patient develop? Define the complication.
3.
List the virulence characteristics of E. coli that are responsible for this syndrome?
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4.
Describe the pathogenic process. In your response address how the infectious
microorganism might be responsible for hemorrhage, anemia, and renal failure.
5.
How is the infection acquired? Include in your answer an explanation of how the most
common vehicle of transmission is likely to cause large outbreaks.
6.
What are the other mechanisms by which E. coli is able to cause diarrhea?
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7.
Should the child be isolated in the hospital?
8.
How does one diagnose the infection?
9.
Should antibiotics be used to treat the child? If so, which ones are used?
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Case History 3
A 59 year old man presents with a one day history of fever, abdominal cramps and diarrhea. His
symptoms began six hours after the onset of the "runs" in two of his grandchildren and their
mother all of whom had been visiting from their dairy and poultry farm in Wisconsin. The day
before becoming ill all had eaten a meal consisting of Caesar salad, pasta with stir fried
vegetables, bread and apples. Other than the abdominal pain and six unformed bowel
movements which contained mucus, he had no complaints.
On examination the man appeared ill. Temperature was 39.3 C, pulse 100 and blood pressure
110/80 standing. He had no rash. The abdomen was tender in the periumbilical area.
WBC
Fecal leukocytes
Fecal occult blood
9.8 X 103 /mm3
Positive
Negative
Stool culture is growing motile, lactose non-fermenting, gram rod that is H2S.
Positive.
1.
What is the likely cause of this man's diarrhea'
2.
Do these organisms cause diarrhea by invasion or toxin production? Describe what is
known of the pathogenesis of diarrhea caused by these organisms?
3.
How did the members of the family become infected? What is the usual route of
infection with this pathogen?
4.
What is the preferred therapy of enteritis due to salmonella?
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5.
What other clinical syndromes are described with salmonella infection?
6.
Given the present distribution systems for meat, poultry and dairy products in the United
States, what measures could be adopted to reduce the spread of salmonella infection?
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Case History 4
A 49- year- old woman presented to the emergency room complaining that she had vomited up
blood at home. She had been suffering with sharp epigastric pain, especially in the morning, for
one week before the vomiting began. The pain was accompanied by mild nausea and was
relieved by food or antacids. She had a long history of peptic ulcer disease and was initially
diagnosed with duodenal ulcer at age16. Despite at least six discrete episodes of ulcer
documented by x-ray or endoscopy, she had never undergone surgery. Workup for
Zollinger-Ellison syndrome (a gastrin producing pancreatic adenoma) was negative.
A nasogastric tube was placed revealing blood in the stomach which cleared after gastric lavage
with iced saline. Immediate endoscopy revealed scarring of the pylorus with a 2 cm ulcer in the
first portion of the duodenum. Biopsy of the ulcer revealed curved bacilli with Warthin-Starry
silver staining and a positive urease test.
1.
Describe the morphologic and microbiologic features of Helicobacter pylori?
2.
What is the frequency of infection with H. pylori in the United States? How does the
distribution of H. pylori infection differ in populations from underdeveloped countries?
3.
What phenotypic characteristics of H. pylori are thought to account for its virulence?
Which of them appear to be most important?
The nasogastric tube aspirate remained blood free and the tube was removed. She was started on
an H2 blocker and the pain rapidly subsided.
4.
What further treatment might be helpful? What long term benefits could she expect if she
were to receive the additional treatment?
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