Question 1

Disease caused by which of the following organisms has fever, abdominal cramping, diarrhea, and stools with gross blood and pus?

Accepted Answer

The symptoms described are typical of an infectious diarrheal disease caused by Campylobacter jejuni. Staphylococcus aureus typically causes food poisoning with rapid onset nausea, vomiting and abdominal cramps. Clostridium difficile causes diarrhea usually with recent antibiotic use, but without blood or pus. Bacillus cereus causes vomiting and diarrhea, but usually without blood or pus.

Question 2

What is the most significant predisposing factor to Clostridium difficile-associated disease?

Accepted Answer

Antimicrobial therapy is the most significant predisposing factor for Clostridium difficile-associated disease because it disrupts the normal gut microbiota, allowing for C. difficile overgrowth and toxin production. Young age, consumption of undercooked beef, and travel to developing countries are not significant predisposing factors.

Question 3

What is the environmental reservoir of Campylobacter?

Accepted Answer

Wild and domestic animals are considered the primary environmental reservoirs of Campylobacter. The bacteria are commonly found in the gastrointestinal tract of many animals, including poultry, cattle, sheep, swine, wild birds, and rodents. Contaminated water and soil can also serve as sources of infection, but these are typically secondary to animal reservoirs. Fish and arthropods are not considered significant sources of Campylobacter infection.

Question 4

What virus causes an acute self-limiting diarrheal illness that is highly contagious through contaminated food, water, fomites, or person-to-person contact and is associated with vomiting and low-grade fever?

Accepted Answer

The described symptoms (acute diarrheal illness, highly contagious through various means, vomiting and low-grade fever) are characteristic of norovirus. Astroviruses and rotaviruses can also cause viral gastroenteritis but do not necessarily present with all of these symptoms. Enteric arenaviruses are not known to cause gastroenteritis in humans.

Question 5

What is the most common cause of bacterial gastroenteritis in the world?

Accepted Answer

Campylobacter jejuni is the most common cause of bacterial gastroenteritis worldwide, causing an estimated 400-500 million infections and 100,000 deaths annually. Salmonella Typhi is the cause of typhoid fever, which is a less common form of gastroenteritis. Shigella sonnei and Yersinia enterocolitica are also less common causes.

Question 6

All of the following organisms can cause enterotoxin-mediated diarrhea, except

Accepted Answer

Salmonella Typhi causes typhoid fever, which is not related to enterotoxin-mediated diarrhea. The other organisms listed can cause enterotoxin-mediated diarrhea.

Question 7

A fecal isolate identified as E. coli produces clear colonies on MacConkey agar with sorbitol. You should suspect

Accepted Answer

E. coli strains that are capable of producing Shiga toxins, also known as verotoxins, are referred to as Enterohemorrhagic E. coli (EHEC). Sorbitol-fermenting E. coli strains are typically indicative of EHEC which often cause severe diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. The inability to ferment sorbitol is one of the key characteristics that differentiate these strains from Enterotoxigenic E. coli (ETEC), which is associated with traveler's diarrhea. Shigella is not capable of fermenting sorbitol and would not grow on MacConkey agar containing sorbitol. Therefore, the correct answer is C) Enterohemorrhagic E. coli.

Question 8

The presence of yellow colonies on thiosulfate-citrate-bile salt-sucrose medium is suggestive of

Accepted Answer

Thiosulfate-citrate-bile salt-sucrose (TCBS) agar is a selective and differential medium used to isolate Vibrio species. Yellow colonies on TCBS agar indicate the fermentation of sucrose, which is characteristic of Vibrio cholerae.

Question 9

What common organism invades the full thickness of the bowel with lymphatic spread?

Accepted Answer

Salmonella Typhi is the only option out of the given organisms that is known to invade the full thickness of the bowel with lymphatic spread. Vibrio cholerae, Campylobacter jejuni, and Aeromonas spp. typically cause infections that are limited to the lining of the intestines.

Question 10

Presence of red colonies with black centers on xylose-lysine-decarboxylase medium is indicative of

Accepted Answer

The presence of red colonies with black centers on xylose-lysine-decarboxylase medium is indicative of nonlactose fermentation and H₂S positive. This is because the medium contains lysine and xylose, which are both substrates that can be used by nonlactose fermenters, and the black center is produced by the breakdown of lysine via the enzyme lysine decarboxylase, which is encoded by the H₂S gene.

Question 11

All of these patient history questions will help focus the search for the cause of diarrhea, except:

Accepted Answer

Asking if the patient ate any hot food is not relevant to the search for the cause of diarrhea. The other three questions are important in guiding the investigation.

Question 12

What type of diarrheal illness produces fever, leukocytosis in peripheral blood, and fecal leukocytes?

Accepted Answer

Diarrhea in which the mucosal surface is invaded by pathogens such as bacteria, parasites, or viruses, can cause an inflammatory response with the production of fever and leukocytosis in peripheral blood, as well as fecal leukocytes being present. Invasion of the full bowel thickness (option B) is more commonly associated with bloody diarrhea, and both endotoxins (option C) and enterotoxins (option D) can cause non-inflammatory diarrhea.

Question 13

What type of diarrheal illness has a rapid onset of symptoms after food ingestion (usually <12 hours)?

Accepted Answer

Diarrhea caused by enterotoxins typically has a rapid onset of symptoms after food ingestion, usually within 12 hours. This is in contrast to diarrhea where the mucosal surface is invaded or diarrhea where the full bowel thickness is invaded, which may have a longer incubation period before symptoms appear. Diarrhea caused by endotoxins is not commonly associated with food ingestion.

Question 14

What is the most common cause of travelers' diarrhea?

Accepted Answer

The most common cause of travelers' diarrhea is Escherichia coli, specifically strains that produce heat-stable enterotoxins. Other pathogens that can cause travelers' diarrhea include Giardia lamblia, Entamoeba histolytica, and Clostridium difficile, but they are less common.

Question 15

What virus is the leading cause of diarrhea in children younger than age 5 years?

Accepted Answer

Rotavirus is the leading cause of diarrhea in children younger than age 5 years, responsible for over 40% of all diarrhea cases in this age group worldwide.

Question 16

All the following organisms invade the bowel mucosal surface to produce diarrhea, except

Accepted Answer

Vibrio cholerae does not invade the bowel mucosal surface to produce diarrhea. Instead, it releases cholera toxin, which causes extensive secretion of fluids and electrolytes from the intestinal cells into the lumen, leading to watery diarrhea. Salmonella spp., Campylobacter spp., and Shigella spp. invade the intestinal mucosa to produce diarrhea.

Question 17

What is the most common cause of death among patients with diarrhea?

Accepted Answer

The most common cause of death among patients with diarrhea is dehydration, which occurs due to loss of fluids and electrolytes from the body. Sepsis and septic shock can occur as complications of severe diarrhea in some cases, but dehydration is the primary cause of mortality. Secondary bacterial infections can also occur but are not as common as dehydration.

Question 18

What defense mechanism does the colon have to guard against infection?

Accepted Answer

The colon has specialized cells that secrete immunoglobulin A (IgA) which is an important defense mechanism against infection in the gut. IgA acts as a barrier by preventing harmful pathogens or toxins from penetrating the mucosal lining and entering the body.

Question 19

What type of diarrheal illness has no fever and no blood or pus in the stool?

Accepted Answer

Diarrhea caused by enterotoxins typically does not involve fever or the presence of blood or pus in the stool, as the toxins affect the intestinal lining and cause an imbalance in electrolytes and water absorption. Examples of enterotoxigenic bacteria include Vibrio cholerae and enterotoxigenic strains of Escherichia coli (ETEC).

Question 20

The urea breath test is a noninvasive test to detect infection caused by

Accepted Answer

The urea breath test is specifically used to detect infection caused by Helicobacter pylori, a bacterium that can cause peptic ulcers and gastritis. It works by measuring the amount of carbon dioxide in a patient's breath after they ingest a small amount of urea that has been labeled with a radioactive or non-radioactive tracer. As H. pylori breaks down the urea, it produces carbon dioxide, which can be detected in the patient's breath.

Quiz 34: Gastrointestinal Infections and Food Poisoning