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What is the cause of intestinal wall bleeding?
What is the purpose of testing for WBC in stool samples?
What types of bacteria are typically included in routine stool cultures?
What is the primary goal of treatment for diarrhea?
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When are antibiotics effective against diarrhea?
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What is the primary mechanism of action of antidiarrheal medications?
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What is the recommended approach to preventing diarrhea when traveling?
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What is the most important measure to prevent diarrhea?
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What percentage of health problems in Ethiopia are attributed to communicable diseases due to unsafe water supply and poor sanitation?
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What is the recommended approach to dealing with nausea and vomiting while traveling?
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Study Notes
Types of Diarrhea
- Acute bloody diarrhea (also called dysentery) and acute watery diarrhea (including cholera) typically last for several hours or days.
- Persistent diarrhea lasts for several weeks (2-4 weeks).
- Chronic diarrhea lasts for more than 5 weeks.
Pathogenesis/Pathophysiology
- Diarrhea occurs when there are subtle abnormalities in input or output at any level of the GI tract, resulting in excessive osmotic load, increased secretion, or diminished fluid resorption.
- The causes of diarrhea include inflammatory, osmotic, secretory, motility, and other factors.
Common Causes of Diarrheal Diseases/Food Poisoning
- Bacterial causes:
- Staphylococcus aureus
- Vibrio cholerae
- Shigella spp.
- Escherichia coli
- Salmonella spp.
- Campylobacter jejuni
- Bacillus cereus
- Clostridium botulinum
- Yersinia enterocolitica
- Non-bacterial causes:
- Viruses (e.g., Rotavirus, Norovirus, Adenovirus, Hepatitis A)
- Parasites (e.g., Giardia lamblia, Entamoeba histolytica)
Invasive Diarrhea
- Caused by bacterial invasion of the bowel mucosal surface
- Organisms involved: Salmonella spp., Campylobacter spp., Shigella spp., E. coli, Vibrio spp.
Shigella Species
- Gram-negative, facultatively anaerobic rods
- Most communicable of the diarrheal bacteria
- Requires a low microbial load
- Symptoms include fever, malaise, fatigue, anorexia, and diarrhea with blood and pus
- Symptoms appear 12-50 hours after exposure
Fecal WBC Lab Test
- Observe blood, WBCs, and pus
- Culture: Colorless colonies on MAC, blue-green colonies on HE, and red/colorless on XLD
Escherichia coli
- Gram-negative, facultative anaerobic rods
- At least five different pathogenic groups cause gastroenteritis:
- ETEC: Enterotoxigenic (cause of traveler's diarrhea)
- EIEC: Enteroinvasive (bacteria dysentery)
- EPEC: Enteropathogenic (diarrhea outbreaks in infants in hospital setting)
- EHEC: Enterohemorrhagic (presence of Shiga-like toxin)
- EAEC: Enteroaggregative (chronic diarrhea in HIV patients, travelers, and children in poor countries)
Enterotoxin-Mediated Diarrhea
- Caused by toxins produced by bacteria
- Examples: S. aureus, Clostridium botulinum, Bacillus cereus, Vibrio cholerae, Enterotoxigenic E. coli
Staphylococcus aureus
- Found on the skin, hair, noses, and throats of people and animals
- Can multiply quickly at room temperature and produce a toxin that causes food poisoning
- Sources: Salads, macaroni, bakery products, cream pies, milk, and dairy products
Clostridium perfringens
- Part of the normal flora of the vagina and GIT
- Produces multiple toxins, including alpha toxin that causes lysis of endothelial and blood cells
- Generates spores in improperly cooked foods
- Causes loss of fluid in intracellular protein
Bacillus cereus
- Gram-positive rods that are spore-forming
- Also acquired by penetrating injuries and intravenous injections
- Produces toxins (diarrheal toxin, emetic toxin)
- Incubation period: 1-6 hours
- Source: Soil, and in raw, dried, and processed foods
- Lab diagnosis: Produces hemolytic colonies on blood agar
Vibrio species
- Gram-negative rods, highly motile, facultative anaerobes, with one to three flagella at one end
- Associated with raw or undercooked seafood harvested from contaminated water
- Infects the small intestine
- Enterotoxin activates adenylate cyclase, which initiates an outpouring of fluid into the intestine
- Watery diarrhea (rice water stools) evident
Lab Diagnosis
- Utilize TCBS media (Thiosulphate Citrate Bile Salt Agar)
- Yellow and profuse colonies
- Inhibits colonic flora
- Differentiates sucrose fermenters from species of Vibrio that are non-fermenters
- Stool contains no RBCs or WBCs since it is toxin-mediated and non-inflammatory
Viral Agents
- Rotavirus: Primarily affects children < 5 years old, spread by fecal-oral route, peak incidence from December to June
- Calicivirus: Norovirus, spread by fecal-oral route, outbreaks on cruise ships, cause of stomach flu
Parasitic Infections
- Giardia lamblia: By ingestion of contaminated water or person-person spread, only lives in the host, chronic infection results in malabsorption syndrome
- Entamoeba histolytica: Exists in cyst and trophozoite form, transmitted by feco-oral with food, water, or hand, symptoms include abdominal discomfort, intense pain in the right side, and dysentery
Diagnosis
- Stool Sample: Direct saline wet mount microscopy, Trichrome Stain (for trophozoites), Biopsy
- Histologically, villi appear flattened
- Fluorescent Antibody Tests
Risk Factors
- Number of ingested organisms: Median infectious dose (ID50)
- Achlorhydria: Inadequate stomach acidity
- Reduction in normal flora: Use of antibiotics
- Age, improper food handling, personal hygiene
Laboratory Dx of Gastrointestinal Pathogens
- Specimen Collection and Handling: Collect within 4 days of onset of symptoms, process ASAP, do not refrigerate
- Fecal Leukocytes: Direct microscopic exam to detect presence of WBCs and RBCs
- Routine stool cultures: Test for Salmonella species, Shigella species, and Campylobacter jejuni
Treatment of Diarrhea
- Patients must be watched for dehydration
- Antibiotics are not effective against viral pathogens, give supportive care for hydration
- Antibiotics may shorten illness due to invasive bacteria or an enterotoxin-mediated process
- Antidiarrheal medications: Decrease bowel motility or the acid (Lomotil, Pepto-Bismol), primarily used with enterotoxin-mediated diarrhea or viral gastroenteritis
Prevention
- Key measures to prevent diarrhea include:
- Access to safe drinking water
- Use of improved sanitation
- Hand washing with soap
- Exclusive breastfeeding for the first 6 months of life
- Good personal and food hygiene
- Health education about how infections spread
- Rotavirus vaccination
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Description
This quiz covers the characteristics of Shigella species, a type of diarrheal bacteria, and how to diagnose it through a fecal WBC lab test. Learn about the symptoms and laboratory tests used to identify Shigella.
