Infectious Diarrhea and Diarrhea Self-Study Flashcards by Matthew Miller

What is the definition of diarrhea?

Passage of abnormally liquid / unformed stool at increased frequency

Stool weight exceeds 200 grams/day (made mostly of water)

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What is acute vs persistent vs chronic diarrhea?

Acute: <2 weeks
Persistent: 2-4 weeks
Chronic: >4 weeks

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What most commonly causes diarrhea and what is on the differential?

Infectious agents more than 90% of the time

Differential:
Med-induced or poison-induced
Ischemic colitis
Diverticulitis
IBD

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What pathogens cause watery diarrhea via entertoxins and usually involve upper small bowel?

Vibrio cholerae
ETEC
Bacillus cereus - reheated rice
Clostridium perfringens

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What pathogens interfere with absorption to cause watery diarrhea?

Giardia
Cryptosporidium - esp. immunocompromised
EPEC
Rotavirus
Norovirus

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What are the most common causes of inflammatory diarrhea in the US?

Campylobacter
Salmonella enteriditis (non-typhoid)
Clostridium difficile
EHEC - in pediatrics

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What are other important causes of inflammatory diarrhea worldwide?

Shigella
Entamoeba histolytica
Salmonella typhi

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What diarrheal pathogens commonly spread systemically via bacteremia?

Typhoid

Non-typhoidal Salmonella

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Which Salmonella / Shigella strains have an animal reservoir?

Only non-typhoid Salmonella (most common in US, normally spread by poultry)

Salmonella typhi / paratyphi and Shigella species are human only

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What cells does Salmonella typhi spread to and what is it’s main virulence factor?

Invades thru M cells then lives intracellularly in macrophages and reticuloendothelial system, including liver and spleen.

Virulence factor includes a Type III secretion system from a Salmonella pathogenicity island which translocates proteins from its intracellular vacuole into the macrophage cytoplasm, preventing maturation of mature phagolysosome.

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What are important intestinal consequences of Salmonella typhi and why?

Host immunologic reaction may contribute to necrosis of Peyer’s patches in severe disease:

Intestinal hemorrhage and/or perforation (distal ileum) are feared complications

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What are the stages of Typhoid fever?

Early constipation or diarrhea for 1-2 weeks (BEFORE fever)

Flu-like symptoms begin by end of first week

Second week - high fever, often with loss of diarrhea, and appearance of rose spots, hepatosplenomegaly, and relative bradycardia

3rd-4th week: Systemic complications

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What are the systemic complications of typhoid fever?

Bacteremia may cause:

Meningitis
Liver abscess
Septic joints / osteoarthritis
Endocarditis
Mycotic aneurysms in atherosclerotic plaques
Immune-complex glomerulonephritis

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How is typhoid fever usually diagnosed?

Blood cultures are usually first.

Cultures of stool, urine, rose spots, and bone marrow may also be positive

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What’s the treatment for typhoid fever?

Fluoroquinolones (flower in sketchy) or ceftriaxone

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What are common reservoirs for nontyphoidal Salmonella?

Birds, poultry, and REPTILES (pet reptiles)

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What membrane changes does Salmonella produce before it tries to invade?

Adhere by means of fimbrae, and then induce cytoskeletal rearrangements inducing formation of “membrane ruffles” that reach out to phagocytose bacteria
-> bacterial-mediated endocytosis

What is the major difference between type of inflammation and disease produced by typhoid and nontyphoidal Salmonella strains?

Nontyphoidal - Neutrophil inflammation and gastroenteritis

Typhoid - monocytic inflammation and significantly less diarrhea

What is the treatment for Salmonella gastroenteritis? How long does it last? What type of diarrhea is it?

Inflammatory but non-bloody, watery diarrhea:

Usually self-limiting infection in 3-7 days

> diagnosis is confirmed by stool culture
> antibiotics not needed / recommended

When are antibiotics needed for nontyphoidal strains?

Usually only with bloodstream infections causing infections of vascular sites, and in immunocompromised patients
-> bacteremia is less common following gastroenteritis

What is the carrier frequency of Salmonella?

Low in both typhoid and nontyphoid (even more so)

-> carriage occurs in gallbladder and leads to biliary abnormalities like stones

What liver and GI tract damage does Salmonella sometimes cause?

Liver - parenchymal necrosis in which hepatocytes are replaced by phagocytic mononuclear infiltrates called typhoid nodules. Can coalesce to cause liver abscess

GI tract - Elongated ulcers, especially in distal ileum

What antibiotic should be given for EHEC?

I tricked you -> antibiotics are not effective in the treatment of EHEC and may promote HUS

What type of E. coli is pathologically similar to Shigella? Which one is only found in pediatrics really & what type of diarrhea does it cause?

EIEC - invasive, like shigella

EPEC - Pediatrics, watery diarrhea

What is the typical cause of Norovirus? Does it affect adults?

Contaminated food / water (buffets), poorly cooked shellfish Typically causes outbreaks of vomiting in winter in adults, but can go year round. Think of Rotavirus as the one which mainly affects you during childhood

What's the treatment for cholera?

Doxycycline 300mg, tetracycline, or azithromycin -> shortens disease course Oral rehydration to prevent hypokalemic hyperchloremic acidosis

By what two mechanisms does the colon determine whether diarrhea is present?

1. Increased colonic load - if small bowel fluid exceed maximal absorptive capacity of colon 2. Altered colonic fluid movement - decreased absorptive ability or net secretion of colon induced

What are some entities which will lead to increased active secretion of solute in the small bowel? Will fasting help this?

1. Cholera 2. VIPoma - stimulates enterocytes to secrete 3. Celiac sprue - crypt hyperplasia with increased secretion Fasting will not help the active secretion. However, fasting would help conditions of decreased absorption (i.e. other mechanism of Celiac sprue, lactose malabsorption)

What is a cause of increased secretion from stomach? How does this contribute to further malabsorption?

Gastrinoma - increased gastric acid and volume Highly increased volumes of gastric acid -> decrease functioning of pancreatic enzymes -> malabsorption

What are the humoral peptides which are secretagogues of interest?

``` VIP - as in VIPoma PGE - as in colitis Gastrin - as in Gastrinoma Serotonin - as in carcinoid syndrome Calcitonin ```

How can lowered motility lead to diarrhea?

Leads to small bowel bacterial overgrowth and diarrhea i.e. glucagonoma

What are some causes of increased secretion (i.e. endogenous laxatives) from colon?

Colon: Bile acid malabsorption (direct secretagogues), fatty acid malabsorption (fatty acids interact with gut bacteria to increased net secretion), colitis (increased PGE)

What is VIPoma also known as and what are its symptoms?

Pancreatic cholera - tumor normally found in pancreatic islets WDHA syndrome: Watery Diarrhea Hypokalemia Achlorhydria

When does bile salt diarrhea occur and what is the effective treatment?

Whenever there is a partial iliectomy (<100 cm lost) -> enough of bile salts are reabsorbed for liver to make enough daily, so you don't have malabsorption, but many bile salts reach colon and act as secretagogues on colonic epithelium Treatment: Cholestyramine - bile salt binding resin

What type of diarrhea occurs when a patient has lost more than 100 cm of distal ileum and what are the associated problems? Will cholestyramine help?

Steatorrhea -> liver cannot make enough bile salts to compensate for loss -> bile salts and fatty acids act as secretagogues as well Associated with cholesterol stones, megaloblastic anemia, and calcium oxalate kidney stones (due to increased fatty acid delivery colon) Cholestyramine will just worsen the problem in this case (less bile salt resorption)

What are the treatments for steatorrhea from short ileum?

Decrease fat intake, use medium chain fatty accids for diet, supplement FADEK, oral calcium to bind oxalate, colectomy may be needed for recurrent stones

What type of anemia will Celiac disease cause? What will a patient need to do in order to test for it?

Iron deficiency - iron absorbed in duodenum, and Celiac affects mostly proximal small bowel Patient will need to be on a gluten diet in order for anti-TTG antibodies to be high enough to test for abnormality

What is the definition of short bowel syndrome? What will the symptoms be?

Less than 1/3 of small bowel left (<200 cm) Symptoms of extreme malabsorption and thus increased diarrhea: - steatorrhea - fluid / electrolyte imbalances - malnutrition - increased gastrin to compensate with further diarrhea

What are the causes of short bowel syndrome?

Surgical, ischemia, radiation, or other disease In children: Often necrotizing enterocolitis Just need at least functional loss of enough bowel to cause it

What are the management options for short bowel syndrome? Long-term complications?

PPIs to decreased acid from increased gastric, antibiotics to stop bacterial overgrowth Parenteral nutrition which can cause vein and liver disease Small bowel +/- liver transplant may be indicated