Gastrointestinal System Infections

Question 1

What is gastroenteritis?

Answer 1

• inflammatory process of the stomach or intestinal mucosal surface
• most commonly associated with ingestion of contaminated foods and/or contaminated water, but more common in developing countries
• can also be caused by infection

Question 2

How does infection cause gastroenteritis?

Answer 2

• pathogen enters gastrointestinal tract via fecal-oral route and multiplies
• delay in appearance of gastrointestinal symptoms (generally 1 – 3 days), while pathogen increases in number or damages invaded tissue
• associated with fever

Question 3

How does intoxication cause gastroenteritis?

Answer 3

• associated with the ingestion of preformed toxin in food or water
• characterized by a sudden appearance of symptoms about 2 – 10 hours after consumption of the exotoxin
• fever rarely a symptom

Question 4

What is acute diarrhea?

Answer 4

• caused by gastroenteritis from intoxication or infection
• increased frequency of stools (3+ BMs/day)
• increased stool volume (> 200 mL of fluid/day excreted in feces)
• stools take the shape of their container

Question 5

Gastroenteritis is characterized by…

Answer 5

1) Abdominal pain/cramping
2) Nausea and vomiting
3) Dehydration
4) Weight loss
5) Fever (infectious)
6) Acute diarrhea (< 2 weeks)

Question 6

What are the 3 clinical syndromes of acute diarrhea?

Answer 6

1) Non-inflammatory or secretory
2) Inflammatory
3) Invasive inflammatory

Question 7

What is non-inflammatory (secretory) diarrhea?

Answer 7

• most common diarrheal syndrome in North America
• typically caused by viruses: norovirus, rotavirus
• more severe attacks caused by bacteria:
  Enterotoxigenic E. coli, Vibrio Cholerae
• associated with some parasites: Giardia intestinalis (beavers)
• characterized by infection of the small intestine leading to large volumes of watery diarrhea
• absence of fecal leukocytes

Question 8

What is inflammatory diarrhea?

Answer 8

• caused by bacteria:
  Shigella spp., Salmonella enterica, Campylobacter jejuni
• associated with some parasites
• characterized by an infection of the colon, causing frequent, small volume loose stools
• blood (gross or occult) often present
• presence of fecal leukocytes and mucous
• can lead to dysentery, a specific term referring to severe diarrhea containing visible blood and often mucous and/or pus

Question 9

What is invasive diarrhea?

Answer 9

• subset of inflammatory diarrhea associated with an invasion of the intestinal mucosa, and increased risk of bacteremia
• caused by bacteria:
  Salmonella spp., Verocytotoxin-producing E. coli
• associated with some parasites

Question 10

What symptoms indicate a need for physician consultation? What does initial evaluation involve?

Answer 10

Any of the following:

• fever (> 38.5°C)
• dysentery
• significant abdominal pain
• dehydration
• Initial evaluation should include patient history, physical exam and screening stool examination
• Further laboratory testing and antimicrobial therapy warranted for specific patients, based on results of initial evaluation

Question 11

What should a patient history include for a patient with gastroenteritis?

Answer 11

• focus on disease severity and risk factors for significant disease
• symptom duration, fever, abdominal pain, nausea, vomiting, and dehydration
• description of diarrhea especially important
• frequency, volume, visible blood, pus or mucous
• investigate potential for common source outbreak
• inquire about friends and relatives with similar symptoms
• past 24 hour diet
• recent travel

Question 12

How are incubation periods relevant for gastroenteritis?

Answer 12

• short incubation periods from time of exposure to onset of symptoms suggests ingestion of a preformed toxin
• ex. Staphylococcal food poisoning and C. perfringens food poisoning have a short incubation period of a few hours, whereas infectious pathogens take longer to cause illness

Question 13

When vomiting is a dominant complaint, suspect…

Answer 13

• viral infection or food poisoning

Question 14

What are risk factors for clinically significant disease?

Answer 14

• age over 70
• neonates
• recent travel or camping
• recent antibiotic use
• immunosuppression
  (prednisone, chemotherapy, HIV/AIDS)

Question 15

What is the purpose of a physical exam for gastroenteritis?

Answer 15

• used to establish severity of disease, specifically, level of dehydration: orthostatic hypotension, tachycardia, decreased skin turgor, dry mucous membranes
• rectal exam recommended if rectal bleeding is indicated; need to determine if due to mechanical erosion or infection

Question 16

What is a screening stool examination?

Answer 16

• fresh cup specimen (orange cap)
• evaluate for fecal leukocytes and occult blood
• presence of leukocytes or blood in feces predictive of positive stool cultures and disease requiring antimicrobial therapy
• positive tests most commonly associated with: Campylobacter jejuni, Salmonella spp., Shigella spp., C. difficile
  and Verocytotoxigenic E. coli

Question 17

When should bacterial cultures be performed?

Answer 17

• all patients with severe or persistent disease (> 1 week)
• positive stool screening examination results with leukocytes or blood
• fever (> 38.5°C)
• grossly bloody stools
• dehydration
• positive cultures are rare (less than 2 - 5%) for patients without fever, occult blood or fecal leukocytes
• cultures not recommended if patient has been in hospital for over 72 hours & has new onset of symptoms

Question 18

When are studies for ova and parasites indicated?

Answer 18

• persistent diarrhea
• international or wilderness travel, daycare centres
• AIDS
• fecal leukocyte negative, but occult blood positive stool
• sensitivity increases to 98% if 3 ova and parasite examinations are performed on 3 separate days
• yellow cap bottle containing formaldehyde that fixes eggs so they can be examined

Question 19

What other non-infectious causes are associated with acute diarrhea?

Answer 19

• IBS
• bowel obstruction
• GI hemorrhage
• medications: metformin, colchicine, diuretics, ACE inhibitors, PPIs magnesium containing antacids
• a broad differential diagnosis should be considered

Question 20

How is diarrhea managed via rehydration and diet?

Answer 20

• rehydration is the focus of initial management
• goal is to pass relatively dilute urine every 2 to 4 hours
• oral fluids (e.g. Pedialyte, Hydralyte) are usually sufficient
• I.V. fluids recommended in cases of severe dehydration or persistent emesis
• patients should eat judiciously until stools are formed (cereals, boiled foods, bananas, crackers)
• dairy-based foods, caffeine and carbonated drinks should be avoided

Question 21

What agents are used to control diarrhea?

Answer 21

• bulking agents
• bismuth compounds (e.g. bismuth subsalicylate)
• antimotility drugs (e.g. loperamide), which should only be used in cases of non-inflammatory (secretory) diarrhea
• antimicrobial therapy indicated in a limited subset of patients
• remember that body is trying to flush out pathogen via diarrhea

Question 22

Why are antibiotics often contraindicated for gastroenteritis? When are they recommended?

Answer 22

• can wipe out normal flora
• only used for clinically significant pathogens or extremes of age
• empiric therapy (ciprofloxacin) recommended for: severe traveller’a diarrhea, dysentery, or patients with high fever and positive stool screening
• once a positive stool culture or parasite examination is identified, antibiotics should be targeted to treat a specific pathogen

Question 23

What infection control implications exist for gastroenteritis?

Answer 23

• prevent transmission: ingestion of contaminated food and water, fecal-oral route, person to person
• use routine practices and contact precautions
• case notification and outbreak notification
• source control to prevent new cases

Question 24

What is Campylobacter jejuni? What are the symptoms of Campylobacter enteritis?

Answer 24

• gram negative, helical shaped bacteria
• infection characterized by: fever,
  abdominal pain and cramping and blood streaked, inflammatory diarrhea (≥10 BM per day)
• symptoms typically resolve within 1 week
• leading cause of foodborne illness in North America
• about 80% of retail chicken is contaminated with C. jejuni
• approximately 60% of cattle excrete the bacterium in feces and milk

Question 25

How is C. jejuni transmitted? How is it controlled?

Answer 25

• transmitted via ingestion of contaminated food and water; fecal-oral route
• infectious dose: 100 - 10,000 organisms
• antibiotic treatment only for severe illness or in those at high risk for severe illness
• hospital: routine practices and contact precautions
• community: hand hygiene after handling raw poultry, cat/dog feces, avoid cross-contamination of uncooked foods with poultry, pasteurization of milk and chlorination of water supply

Question 26

What is Salmonella enterica? What two conditions does it cause?

Answer 26

• gram negative, bacillus-shaped bacteria
• associated with 2 conditions:
  1) Typhoid (enteric) fever (Typhi and Paratyphi serotypes)
  2) Salmonellosis (Enteritidis and Typhimurium serotypes)
• invades and multiplies within intestinal mucosa
• Typhi and Paratyphi serotypes may subsequently enter the bloodstream causing a more serious infection, lasting up to 4 weeks – requires antibiotic therapy due to risk of life threatening complications

Question 27

How do Typhi and Paratyphi serotypes move into the bloodstream?

Answer 27

• salmonella trigger endocytosis via invasins into the epithelial cells
• salmonella kills host cell and moves into bloodstream
• travel through bloodstream via phagocytes into liver, spleen, bone and gallbladder – causing secondary infections
• carriers may shed the pathogen for > 6 months even when aymptomatic
• causes typhoid fever

Question 28

What is salmonellosis?

Answer 28

• Salmonella infection characterized by: fever, nausea, loss of appetite, headache, myalgias, malaise, abdominal pain and cramps, and inflammatory diarrhea (negative for blood in most cases, positive for fecal leukocytes)
• symptoms typically resolve within 1- 2 weeks, and generally require supportive therapy only; antibiotics reserved for severe cases

Question 29

How is salmonellosis transmitted and controlled?

Answer 29

• transmitted via ingestion of contaminated food/water (raw or undercooked meat, eggs, raw fruits and veg, seafood)
• also transmitted via fecal-oral route from people and pet turtles and iguanas
• hospital: routine practices and contact precautions
• community: good sanitation practices to deter food contamination, proper refrigeration to prevent increases in bacterial numbers, avoid cross-contamination of uncooked foods with raw foods that may contain Salmonella enterica, good hand hygiene after handling animals (e.g. turtles)

Question 30

What is Enterotoxigenic E. coli (ETEC)?

Answer 30

• gram negative, bacillus-shaped bacteria
• produces an enterotoxin similar to V. Cholerae
• commonly referred to as “Traveler’s Diarrhea”
• infection characterized by watery, non-inflammatory diarrhea, 4-5 loose/watery stools per day, abdominal cramps, nausea and vomiting, mild fever, bloating
• symptoms typically resolve in 1 – 3 days
• in severe cases, patients will experience dehydration, bloody stools (due to microfissures) , persistent vomiting, and high fever (> 38.9°C)

Question 31

What is the action of the cholera toxin in the intestinal epithelial cells?

Answer 31

• A-B toxin
• active portion enters cell and activated adenylate cyclase
• increase cAMP
• cAMP stimulates cells to secrete Cl, Na, and other electrolytes
• water follows electrolytes into the intestinal lumen, causing secretory diarrhea

Question 32

How is ETEC transmitted and controlled?

Answer 32

• transmission via ingestion of contaminated food and water and person to person (fecal-oral)
• infectious dose: 100 organisms
• antibiotic treatment reserved for severe cases
• vaccine available (Dukoral)
• hospital: routine practices and contact precautions
• community: “boil it, cook it, peel it, or forget it” and avoid consuming non-sterile sources of water

Question 33

What is Dukoral?

Answer 33

• oral vaccine for preventing ETEC and V. Cholerae
• used for adults and children at least 2 years of age
• contains killed V. Cholerae and attenuated V. Cholerae enterotoxin
• administered in 2 doses, 1 – 6 weeks apart
• confers 3 months of protection
• often taken prior to travel

Question 34

What is Verocytotoxigenic E. coli (VTEC)?

Answer 34

• also gram negative, rod-shaped
• E. coli 0157:H7 is most common strain in Canada
• also referred to as enterohemorrhagic E. coli (EHEC)
• produces a verocytotoxin that damages intestinal mucosa, causing lesions and bleeding; can bind to neutrophils
• infection characterized by: inflammatory diarrhea (10+ bowel movements/day), abdominal cramping, pain or tenderness, and low-grade fever (30% of patients)
• hemorrhagic colitis occurs in 6% of infected patients typically 24 hours after symptom onset
• symptom resolution within 1 week in healthy adult

Question 35

How is VTEC transmitted and controlled?

Answer 35

• transmitted via contaminated milk, fruit juice, ground beef, and produce (spinach, sprouts), and person to person (fecal-oral)
• hospital: routine practices and contact precautions
• community: avoid consuming non-sterile sources of water, observe public health notifications related to contaminated foods, proper cooking of contaminated meats

Question 36

What is hemolytic uremic syndrome?

Answer 36

• rare complication of VTEC associated age extremes
• occurs 3-7 days after symptom onset
• verocytotoxin invades bloodstream and destroys RBCs
• damaged RBCs clog microvasculature in the kidney, causing kidney failure
• aggravated by anti-motility drugs and antibiotics
• leading cause of acute kidney failure in children
• most cases resolve with no long-term consequences

Question 37

What are signs and symptoms of hemolytic uremic syndrome?

Answer 37

• fever, abdominal pain
• pale skin tone, fatigue and irritability d/t low RBCs
• unexplained small bruises or bleeding from nose or mouth
• decreased urination
• swelling of the face, hands and feet (sometimes whole body)

Question 38

How is hemolytic uremic syndrome treated?

Answer 38

• red blood cell and platelet transfusions, plasma exchange, kidney dialysis

Question 39

What is Shigella spp.?

Answer 39

• gram negative, rod-shaped bacteria
• S. Sonnei most common species in North America
• children between 2 and 4 years of age most susceptible
• produce invasins, and an enterotoxin similar to V. Cholerae

Question 40

How is shigellosis transmitted and controlled?

Answer 40

• transmitted via contaminated food and water, person to person contact (fecal-oral route)
• most commonly associated with poor hygienic conditions and overcrowding
• infectious dose: 10-100 organisms
• hospital: routine practices and contact precautions
• community: good sanitation practices to deter food contamination and proper hygiene

Question 41

What is shigellosis?

Answer 41

• infection from shigella bacterium characterized by inflammatory diarrhea; often bloody and may contain mucous
• abdominal cramps, rectal pain, fever, nausea
• symptoms typically resolve in health adults in 2-3 days
• carrier for about 4 weeks
• antibiotic treatment in severe cases only; dysentery (Shigella dysenteriae) associated with severe purulent bloody stools; produces Shiga toxin similar to the exotoxin produced by VTEC

Question 42

Can Shigella spp. cause sepsis?

Answer 42

No; is able to enter colon cells and enter bloodstream, but is quickly wiped out by immune defences

Question 43

What is Clostridium difficile?

Answer 43

• gram positive endospore-forming bacteria
• produce exotoxins that cause inflammation of the colon accompanied by increased fluid secretion and permeability of intestinal mucosa
• enterotoxin (Toxin A): diarrhea & inflammation
• cytotoxin (Toxin B): induces cell damage & facilitates lesion formation
• NAP1 strain: associated with serious hospital outbreaks and more severe disease; produces more toxin (A&B) than previous strains
• infections associated with hospitals and nursing homes

Question 44

Why is a C. diff infection also called “antibiotic-associated diarrhea”?

Answer 44

• nutrients are typically limited for this organism when the spore is in the human gut (due to normal flora)
• can gain access to nutrients and grow when antibiotics wipe out normal flora
• suspect C. diff in any client who has diarrhea in association to broad-spectrum antibiotic exposure (≤ 2 months of symptoms)
• fluoroquinolones, clindamycin, penicillins

Question 45

What are symptoms of C. difficile infection?

Answer 45

• watery, foul smelling diarrhea, mild abdominal cramping and tenderness
• can advance to pseudomembranous colitis; life threatening complication associated with declining host factors

Question 46

What is pseudomembranous colitis?

Answer 46

• overgrowth of C. diff
• > 10 bloody stools per day with or without pus
• intestinal mucosal lesions from CT, dying leukocytes, and dead cells appearing as small, raised yellowish plaques

Question 47

How is C. diff infection treated?

Answer 47

• discontinuation of implicated antimicrobial agent and supportive therapy
• metronidazole or vancomycin to target C. diff if symptoms do not resolve
• probiotics
• relapse in 10-20% patients, fecal transplants may be required if frequent relapses

Question 48

Vancomycin is highly specific to…

Answer 48

Gram positive organisms

Question 49

What are some complications of C. diff infection?

Answer 49

• bowel perforation; due to damage to intestinal wall

- toxic megacolon; gross distension of colon putting pressure on other organs

Question 50

What infection control precautions exist for C. diff?

Answer 50

Contact precautions and isolation for all patients, do not share equipment, ensure consistent environmental cleaning and disinfection, hand washing with soap and water preferred due to absence of sporicidal activity in waterless antiseptic handwashes

Question 51

Viral gastroenteritis are generally less…

Answer 51

Severe than bacterial gastroenteritis

Question 52

What are common symptoms of viral gastroenteritis?

Answer 52

• secretory diarrhea
• abdominal cramping
• nausea and vomiting
• fever, chills, and clammy skin
• weight loss and lack of appetite
• symptoms appear within 24 hours of infection and resolve within 12 to 60 hours after symptom onset

Question 53

How do viruses cause gastroenteritis?

Answer 53

• viruses infect epithelial cells of the intestinal tract where all undergo lytic replication
• as the host cell’s die, the normal function of the GI tract is lost
• self-limiting
• once epithelial layer is destroyed, replacement cells grow and function is restored
• transmitted via contaminated food and water (fecal-oral), person to person, aerosols from vomit

Question 54

What is rotavirus?

Answer 54

• incubation period of 2 - 3 days
• most common in children between 6 months and 2 years of age
• accounts for ~ 50% of all cases of childhood diarrhea requiring hospitalization (due to dehydration)
• symptoms persist (high fever, vomiting, diarrhea) for 1 week
• peak incidence in February and May
• infection control via routine practices and contact precautions
• infected children shed about 1000 organisms per gram of stool
• oral vaccine administered at 2 and 4 months of age

Question 55

What is norovirus?

Answer 55

• leading cause of viral gastroenteritis
• transmitted via fecal-oral route, direct contact with oral secretions, contaminated fomites and aerosolized vomit
• infectious dose: 10 organisms
• incubation period of 12 – 48 hours
• symptoms include; secretory diarrhea, nausea and vomiting, stomach cramps, fatigue, low grade fever, chills, headache
• symptoms persist for approximately 2 – 3 days
• patients can shed asymptomatically for up to 14 days post resolution of symptoms
• can live on hard surfaces for up to 3 weeks
• resistant to many disinfectants
• require routine and contact precautions, cohort affected patients to separate rooms
• good hand hygiene
• supportive treatment only

Question 56

What are intoxications?

Answer 56

• associated with the ingestion of preformed toxin
• often referred to as “food poisoning“
• nausea, vomiting, abdominal cramps and diarrhea, in the absence of fever, suggests food poisoning
• especially if symptoms occur within 1 to 16 hours after exposure and resolve in less than 24 hours
• symptoms associated with enterotoxin production
• common causes of intoxications include
  Staphylococcus aureus and Clostridium perfringens

Question 57

What foods are commonly associated with intoxications?

Answer 57

• processed meats, custard pastries, potato salad, ham, meat stews
• contamination often results from food contamination by a food handler with a superficial staphylococcal infection

Question 58

What treatment exists for intoxications?

Answer 58

• fluid replacement (oral rehydration usually sufficient)

- antiemetic drugs

Question 59

What is a Staphylococcus aureus intoxication?

Answer 59

• gram positive cocci-shaped bacteria
• produces an enterotoxin that is heat stable and can survive roughly 30 minutes of boiling
• once toxin is formed, it cannot be destroyed – even if food is reheated
• takes ~ 2 hours for bacteria to grow and secrete toxin
• causes no obvious sign of spoilage or change in the food’s taste
• self-limiting illness, no treatment necessary
• oral rehydration sufficient in cases of mild dehydration