Gastroenteritis

Campylobacter

Pathogen

• Campylobacter Campylobacter Campylobacter ("curved bacteria") is a genus of thermophilic, S-shaped, gram-negative bacilli. There are many species of Campylobacter, with C. jejuni and C. coli most commonly implicated in human disease. Campylobacter jejuni are curved, gram-negative, oxidase-positive rods with polar flagella.
• Distinguishing features: 
  • Require a CO₂-rich environment
  • Grow at 42.0°C (107.6°F)
  • May appear S-shaped or like seagull wings due to their helical structure
• The most common pathogen responsible for foodborne gastroenteritis in the United States
• Highly contagious

Transmission

• Fecal-oral
• Foodborne (undercooked poultry and unpasteurized milk) and contaminated water
• Direct contact with infected animals (cats, dogs, pigs) or animal products

Pathogenesis

• Invades the mucosa of the intestines → produces endotoxins, enterotoxins, and cytotoxins → destroys mucosal surfaces → blood and pus in stools (inflammatory diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea)
• Rarely penetrates to cause septicemia

Clinical presentation

• Acute watery and bloody diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
• Fever
• Severe right lower quadrant abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain resembling appendicitis Appendicitis Appendicitis is the acute inflammation of the vermiform appendix and the most common abdominal surgical emergency globally. The condition has a lifetime risk of 8%. Characteristic features include periumbilical abdominal pain that migrates to the right lower quadrant, fever, anorexia, nausea, and vomiting. Appendicitis (“pseudoappendicitis”)
• Headache
• Myalgias

Management

• Most cases will have a spontaneous resolution.
• Macrolides Macrolides Macrolides and ketolides are antibiotics that inhibit bacterial protein synthesis by binding to the 50S ribosomal subunit and blocking transpeptidation. These antibiotics have a broad spectrum of antimicrobial activity but are best known for their coverage of atypical microorganisms. Macrolides and Ketolides and fluoroquinolones
• A 3rd-generation cephalosporin, imipenem, ampicillin, or gentamicin can be given for extraintestinal infections.

Complications

• Guillain-Barré syndrome Guillain-Barré syndrome Guillain-Barré syndrome (GBS), once thought to be a single disease process, is a family of immune-mediated polyneuropathies that occur after infections (e.g., with Campylobacter jejuni). Guillain-Barré Syndrome (cross-reaction between C. jejuni antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins and human gangliosides)
• Reactive arthritis Reactive arthritis Reactive arthritis is a seronegative autoimmune spondyloarthropathy that occurs in response to a previous gastrointestinal (GI) or genitourinary (GU) infection. The disease manifests as asymmetric oligoarthritis (particularly of large joints in the lower extremities), enthesopathy, dactylitis, and/or sacroiliitis. Reactive Arthritis (in HLA-B27–positive patients)
• Hemolytic anemia Hemolytic Anemia Hemolytic anemia (HA) is the term given to a large group of anemias that are caused by the premature destruction/hemolysis of circulating red blood cells (RBCs). Hemolysis can occur within (intravascular hemolysis) or outside the blood vessels (extravascular hemolysis). Hemolytic Anemia
• Endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis and myopericarditis
• Meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis

Non-typhoidal Salmonella

Pathogen

• S. enteritidis and S. typhimurium are gram-negative, non–lactose fermenting bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview.
• Produce hydrogen sulfide and are motile (unlike Shigella Shigella Shigella is a genus of gram-negative, non-lactose-fermenting facultative intracellular bacilli. Infection spreads most commonly via person-to-person contact or through contaminated food and water. Humans are the only known reservoir. Shigella)
• The 2nd most common pathogen responsible for bacterial foodborne gastroenteritis

Transmission

• Foodborne bacterial infection (poultry, raw eggs, milk)
• Reservoir: enteric tracts of humans and domestic animals (turtles, reptiles, chickens)
• Salmonella Salmonella Salmonellae are gram-negative bacilli of the family Enterobacteriaceae. Salmonellae are flagellated, non-lactose-fermenting, and hydrogen sulfide-producing microbes. Salmonella enterica, the most common disease-causing species in humans, is further classified based on serotype as typhoidal (S. typhi and paratyphi) and nontyphoidal (S. enteritidis and typhimurium). Salmonella is sensitive to stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach acid. Lowered stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach acidity (antacids or gastrectomy) increases the risk for infection.
• Other risk factors: 
  • Hemolytic conditions (sickle cell anemia, malaria Malaria Malaria is an infectious parasitic disease affecting humans and other animals. Most commonly transmitted via the bite of a female Anopheles mosquito infected with microorganisms of the Plasmodium genus. Patients present with fever, chills, myalgia, headache, and diaphoresis. Malaria)
  • Splenectomy
  • Cirrhosis Cirrhosis Cirrhosis is a late stage of hepatic parenchymal necrosis and scarring (fibrosis) most commonly due to hepatitis C infection and alcoholic liver disease. Patients may present with jaundice, ascites, and hepatosplenomegaly. Cirrhosis can also cause complications such as hepatic encephalopathy, portal hypertension, portal vein thrombosis, and hepatorenal syndrome. Cirrhosis
  • Leukemia and lymphoma
  • HIV infection HIV infection Human immunodeficiency virus (HIV), a single-stranded RNA virus belonging to the Retroviridae family, is the etiologic agent of acquired immunodeficiency syndrome (AIDS). The human immunodeficiency virus is a sexually transmitted or blood-borne infection that attacks CD4+ T lymphocyte cells, macrophages, and dendritic cells, leading to eventual immunodeficiency. HIV Infection and AIDS

Pathogenesis

• Bacteria invade the mucosa in the ileocecal region and are released into the lamina propria → influx of neutrophils → inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation → ↑ prostaglandins and cAMP → loose diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea and necrosis of the upper mucosa
• Septicemia is not common (< 5%) with S. enteritidis, but may occur with other subtypes.

Clinical presentation

• Incubation period of 8–72 hours, lasts 3–7 days
• Inflammatory watery diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea (occasionally bloody) 
• Fever, chills
• Headache
• Myalgias
• Severe vomiting 
• Abdominal cramping

Management

• Supportive care
• Antibiotics:
  • Not required for most uncomplicated cases
  • Prolongs fecal excretion of the pathogen
  • Only indicated for systemic manifestations or severe diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea:
    • Fluoroquinolones Fluoroquinolones Fluoroquinolones are a group of broad-spectrum, bactericidal antibiotics inhibiting bacterial DNA replication. Fluoroquinolones cover gram-negative, anaerobic, and atypical organisms, as well as some gram-positive and multidrug-resistant (MDR) organisms. Fluoroquinolones (ciprofloxacin) 
    • TMP-SMX 
    • Azithromycin
    • 3rd-generation cephalosporins Cephalosporins Cephalosporins are a group of bactericidal beta-lactam antibiotics (similar to penicillins) that exert their effects by preventing bacteria from producing their cell walls, ultimately leading to cell death. Cephalosporins are categorized by generation and all drug names begin with "cef-" or "ceph-." Cephalosporins (ceftriaxone)

Complications

• Bacteremia
• Reactive arthritis Reactive arthritis Reactive arthritis is a seronegative autoimmune spondyloarthropathy that occurs in response to a previous gastrointestinal (GI) or genitourinary (GU) infection. The disease manifests as asymmetric oligoarthritis (particularly of large joints in the lower extremities), enthesopathy, dactylitis, and/or sacroiliitis. Reactive Arthritis
• Osteomyelitis Osteomyelitis Osteomyelitis is an infection of the bone that results from the spread of microorganisms from the blood (hematogenous), nearby infected tissue, or open wounds (non-hematogenous). Infections are most commonly caused by Staphylococcus aureus. Osteomyelitis (particularly in sickle cell patients)
• Meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis 
• Myocarditis Myocarditis Myocarditis is an inflammatory disease of the myocardium, which may occur alone or in association with a systemic process. There are numerous etiologies of myocarditis, but all lead to inflammation and myocyte injury, most often leading to signs and symptoms of heart failure. Myocarditis, endocarditis

Shigella

Shigella Shigella Shigella is a genus of gram-negative, non-lactose-fermenting facultative intracellular bacilli. Infection spreads most commonly via person-to-person contact or through contaminated food and water. Humans are the only known reservoir. Shigella causes bacilliary dysentery, also known as shigellosis.

Pathogen

• S. dysenteriae, S. flexneri, S. sonnei, and S. boydii are gram-negative rods.
• Gastric acid resistant
• S. dysenteriae type 1 produces Shiga toxin (enterotoxin).

Transmission

• Fecal-oral
• Humans are the only natural reservoir.
• Flies are vectors.
• Foodborne (unpasteurized milk products and raw, unwashed vegetables)
• Contaminated water
• Highly contagious

Pathogenesis

• Shigella Shigella Shigella is a genus of gram-negative, non-lactose-fermenting facultative intracellular bacilli. Infection spreads most commonly via person-to-person contact or through contaminated food and water. Humans are the only known reservoir. Shigella invades M cells through macropinocytosis → taken up by macrophages → escapes its phagosome → reaches epithelial cytoplasm and replicates → induces inflammatory response → epithelial and immune cell death Cell death Injurious stimuli trigger the process of cellular adaptation, whereby cells respond to withstand the harmful changes in their environment. Overwhelmed adaptive mechanisms lead to cell injury. Mild stimuli produce reversible injury. If the stimulus is severe or persistent, injury becomes irreversible. Apoptosis is programmed cell death, a mechanism with both physiologic and pathologic effects. Cell Injury and Death
• Polymerized actin filaments are used to spread cell-to-cell without needing to re-enter the extracellular milieu.
• Shiga toxin release by S. dysenteriae:
  • Has 3 properties: neurotoxic, cytotoxic, enterotoxic
  • Causes intestinal secretion of solutes and water
  • Can induce HUS
• Resulting effects:
  • Watery diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
  • Mucus secretion
  • Leukocyte infiltration 
  • Superficial ulcers 
  • Rarely causes invasion of blood vessels

Clinical presentation

• Incubation period of 0–48 hours, lasts 2–7 days
• Fever
• Abdominal cramping
• Tenesmus (urgency to defecate)
• Inflammatory diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea with mucus, pus, and blood

Antibiotics

• Usually resolves spontaneously
• Rehydration and electrolyte replacement may be needed.
• Antibiotics shorten the duration of symptoms and pathogen shedding in the stool:
  • Fluoroquinolones Fluoroquinolones Fluoroquinolones are a group of broad-spectrum, bactericidal antibiotics inhibiting bacterial DNA replication. Fluoroquinolones cover gram-negative, anaerobic, and atypical organisms, as well as some gram-positive and multidrug-resistant (MDR) organisms. Fluoroquinolones
  • Azithromycin
  • 3rd-generation cephalosporins Cephalosporins Cephalosporins are a group of bactericidal beta-lactam antibiotics (similar to penicillins) that exert their effects by preventing bacteria from producing their cell walls, ultimately leading to cell death. Cephalosporins are categorized by generation and all drug names begin with "cef-" or "ceph-." Cephalosporins
• Avoid antimotility medications, because they can worsen symptoms and may lead to toxic megacolon Megacolon Megacolon is a severe, abnormal dilatation of the colon, and is classified as acute or chronic. There are many etiologies of megacolon, including neuropathic and dysmotility conditions, severe infections, ischemia, and inflammatory bowel disease. Megacolon.

Complications

• HUS → due to Shiga toxin, often seen in children
• Acute blood loss → mucosal ulcerations
• Intestinal complications: 
  • Toxic megacolon Megacolon Megacolon is a severe, abnormal dilatation of the colon, and is classified as acute or chronic. There are many etiologies of megacolon, including neuropathic and dysmotility conditions, severe infections, ischemia, and inflammatory bowel disease. Megacolon
  • Colonic perforation
  • Intestinal obstruction 
  • Proctitis
  • Rectal prolapse Rectal prolapse Rectal prolapse, also known as rectal procidentia, is the protrusion of rectal tissue through the anus. The tissue may include just the mucosa or the full thickness of the rectal wall. Common risk factors include chronic straining, constipation, bowel motility disorders, and weakening of the pelvic floor muscles. Rectal Prolapse → due to tenesmus
• Reactive arthritis Reactive arthritis Reactive arthritis is a seronegative autoimmune spondyloarthropathy that occurs in response to a previous gastrointestinal (GI) or genitourinary (GU) infection. The disease manifests as asymmetric oligoarthritis (particularly of large joints in the lower extremities), enthesopathy, dactylitis, and/or sacroiliitis. Reactive Arthritis 
• Though invasive, Shigella Shigella Shigella is a genus of gram-negative, non-lactose-fermenting facultative intracellular bacilli. Infection spreads most commonly via person-to-person contact or through contaminated food and water. Humans are the only known reservoir. Shigella only rarely causes septicemia.

Yersinia

Pathogen

• Yersinia Yersinia Yersinia is a genus of bacteria characterized as gram-negative bacilli that are facultative anaerobic with bipolar staining. There are 2 enteropathogenic species that cause yersiniosis, Y. enterocolitica and Y. pseudotuberculosis. Infections are manifested as pseudoappendicitis or mesenteric lymphadenitis, and enterocolitis. Enterobacteriaceae: Yersinia spp./Yersiniosis enterocolitica are gram-negative, oxidase-negative coccobacilli.
• Facultative anaerobes
• Pleomorphic bacterium that belongs to Enterobacteriaceae
• Obligate pathogen
• Distinguishing features:
  • Motile at 25.0°C (77°F), nonmotile at 37.0°C (98.6°F)
  • Cold growth

Transmission

• Foodborne (raw or undercooked pork, unpasteurized milk)
• Blood products
• Contaminated water
• Direct or indirect contact with an infected animal (livestock, rabbits, rodents)

Pathogenesis

• Adheres to epithelial cells in the ileum → invades the intestinal wall, likely through M cells → colonizes lymphoid tissue (Peyer’s patches)
• Can invade mesenteric lymph nodes and disseminate
• Enterotoxin production similar to ETEC
• Leads to mucosal ulceration in the terminal ileum
• Iron overload states increase the pathogenicity.

Clinical presentation

• Incubation period is around 4–6 days; the duration is 1–2 weeks.
• Inflammatory bloody diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
• Fever
• Nausea and vomiting
• Abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
• Pharyngitis Pharyngitis Pharyngitis is an inflammation of the back of the throat (pharynx). Pharyngitis is usually caused by an upper respiratory tract infection, which is viral in most cases. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and hoarseness. Pharyngitis (approximately 20%)

Management

• Generally only requires supportive care
• Antibiotics may be used based on severity, but there is questionable clinical benefit:
  • Fluoroquinolones Fluoroquinolones Fluoroquinolones are a group of broad-spectrum, bactericidal antibiotics inhibiting bacterial DNA replication. Fluoroquinolones cover gram-negative, anaerobic, and atypical organisms, as well as some gram-positive and multidrug-resistant (MDR) organisms. Fluoroquinolones 
  • TMP-SMX
  • 3rd-generation cephalosporins Cephalosporins Cephalosporins are a group of bactericidal beta-lactam antibiotics (similar to penicillins) that exert their effects by preventing bacteria from producing their cell walls, ultimately leading to cell death. Cephalosporins are categorized by generation and all drug names begin with "cef-" or "ceph-." Cephalosporins

Complications

• Reactive arthritis Reactive arthritis Reactive arthritis is a seronegative autoimmune spondyloarthropathy that occurs in response to a previous gastrointestinal (GI) or genitourinary (GU) infection. The disease manifests as asymmetric oligoarthritis (particularly of large joints in the lower extremities), enthesopathy, dactylitis, and/or sacroiliitis. Reactive Arthritis
• Erythema nodosum Erythema nodosum Erythema nodosum is an immune-mediated panniculitis (inflammation of the subcutaneous fat) caused by a type IV (delayed-type) hypersensitivity reaction. It commonly manifests in young women as tender, erythematous nodules on the shins. Erythema Nodosum
• Systemic infection
• Abdominal (rare): 
  • Mesenteric lymphadenitis (“pseudoappendicitis” with right lower quadrant pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain)
  • Mesenteric vein thrombosis (can lead to bowel necrosis)
  • Bowel perforation
  • Toxic megacolon Megacolon Megacolon is a severe, abnormal dilatation of the colon, and is classified as acute or chronic. There are many etiologies of megacolon, including neuropathic and dysmotility conditions, severe infections, ischemia, and inflammatory bowel disease. Megacolon
  • Cholangitis
  • Peritonitis

Clostridium

Clostridium perfringens enterocolitis will be discussed here.

Pathogen

• Clostridium perfringens type A are gram-positive, anaerobic, spore-forming rods.
• Distinguishing features:
  • Non-motile
  • Anaerobic: “stormy fermentation” in milk media
  • Double zone of hemolysis on blood agar

Transmission

• Foodborne (undercooked or poorly refrigerated meat, reheated meat dishes, legumes)
• Spores can survive cooking temperatures.
• Proliferates on foods that are improperly stored

Pathogenesis

• Spores germinate under anaerobic conditions.
• Enterotoxin is produced in the intestines → disrupts ion transport → watery diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, cramps

Clinical presentation

• Incubation period of 6–24 hours, resolves within 24–48 hours (usually < 24 hours)
• Severe abdominal cramping
• Non-inflammatory, watery diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
• Vomiting and fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever are uncommon.

Management

• Supportive care 
• Usually a self-limited disease

Other pathologic manifestations

• Gas gangrene Gas gangrene Gas gangrene, also known as clostridial myonecrosis, is a life-threatening muscle and soft tissue infection that usually develops after traumatic inoculation with Clostridium perfringens (C. perfringens), but can also develop spontaneously in association with other Clostridium species. Gas Gangrene
• Cellulitis Cellulitis Cellulitis is a common infection caused by bacteria that affects the dermis and subcutaneous tissue of the skin. It is frequently caused by Staphylococcus aureus and Streptococcus pyogenes. The skin infection presents as an erythematous and edematous area with warmth and tenderness. Cellulitis and fasciitis
• Necrotizing enterocolitis Necrotizing enterocolitis Necrotizing enterocolitis (NEC) is an intestinal inflammatory process that can lead to mucosal injury and necrosis. The condition is multifactorial, with underlying risk factors that include prematurity and formula feeding. The clinical presentation varies in severity from feeding intolerance, acute findings on abdominal exam, and systemic symptoms. Necrotizing Enterocolitis (from type C strains):
  • Beta-toxin produces segmental necrosis of the intestine.
  • Presents with bloody diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, and vomiting
  • Treatment:
    • Antibiotics (penicillin G, metronidazole)
    • Possible surgery for failure to respond, perforation, or obstruction

Rotavirus

Pathogen

• Rotavirus Rotavirus Rotavirus belongs to the Reoviridae family and is a non-enveloped, double-stranded RNA virus. Transmission occurs through the fecal-oral route. Rotavirus is a common cause of severe gastroenteritis in children. Severe infections can result in dehydration and death. Reoviridae: Rotavirus is a non-enveloped, segmented, double-stranded RNA RNA Ribonucleic acid (RNA), like deoxyribonucleic acid (DNA), is a polymer of nucleotides that is essential to cellular protein synthesis. Unlike DNA, RNA is a single-stranded structure containing the sugar moiety ribose (instead of deoxyribose) and the base uracil (instead of thymine). RNA generally carries out the instructions encoded in the DNA but also executes diverse non-coding functions. RNA Types and Structure reovirus.
• The most common cause of severe diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea among infants and children worldwide

Transmission

• Fecal-oral route
• Only a small inoculum is required for transmission.
• Common during the winter months

Pathophysiology

• Penetrates cells of the small intestinal villi → cholera toxin–like protein production → destruction and blunting of the microvilli → disrupts electrolyte and water absorption
• ↓ disaccharidase activity → malabsorption Malabsorption Malabsorption involves many disorders in which there is an inability of the gut to absorb nutrients from dietary intake, potentially including water and/or electrolytes. A closely related term, maldigestion is the inability to break down large molecules of food into their smaller constituents. Malabsorption and maldigestion can affect macronutrients (fats, proteins, and carbohydrates), micronutrients (vitamins and minerals), or both. Malabsorption and Maldigestion of lactose and D-xylose → osmotic influx into the intestine 
• Watery stools develop due to active water secretion and impaired absorption.

Clinical presentation

• Incubation period is < 48 hours, and the duration is 4–5 days.
• Fever
• Malaise
• Abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
• Vomiting
• Non-inflammatory, non-bloody, watery diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea: can be severe and lead to serious dehydration

Management and prevention

• Disease is self-limited.
• Oral rehydration
• IV fluids in patients with severe dehydration
• Live attenuated vaccine Vaccine A vaccine is usually an antigenic, non-virulent form of a normally virulent microorganism. Vaccinations are a form of primary prevention and are the most effective form due to their safety, efficacy, low cost, and easy access. Vaccination: 
  • Given to all children before 8 months of age 
  • Contraindications:
    • Severe combined immunodeficiency Severe Combined Immunodeficiency Severe combined immunodeficiency (SCID), also called "bubble boy disease," is a rare genetic disorder in which the development of functional B and T cells is disturbed due to several genetic mutations that result in reduced or absent immune function. Severe Combined Immunodeficiency disease (SCID)
    • History of intussusception Intussusception Intussusception occurs when a part of the intestine (intussusceptum) telescopes into another part (intussuscipiens) of the intestine. The condition can cause obstruction and, if untreated, progress to bowel ischemia. Intussusception is most common in the pediatric population, but is occasionally encountered in adults. Intussusception

Complications

• Seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures
• Encephalopathy
• Encephalitis Encephalitis Encephalitis is inflammation of the brain parenchyma caused by an infection, usually viral. Encephalitis may present with mild symptoms such as headache, fever, fatigue, and muscle and joint pain or with severe symptoms such as seizures, altered consciousness, and paralysis. Encephalitis

Norovirus

Pathogen and epidemiology

• Norovirus Norovirus Norovirus is a nonenveloped, single-stranded, positive-sense RNA virus belonging to the Caliciviridae family. Norovirus infections are transmitted via the fecal-oral route or by aerosols from vomiting. The virus is one of the most common causes of nonbacterial gastroenteritis epidemic worldwide. Symptoms include watery and nonbloody diarrhea, nausea, vomiting, and low-grade fever. Norovirus (also known as Norwalk virus Virus Viruses are infectious, obligate intracellular parasites composed of a nucleic acid core surrounded by a protein capsid. Viruses can be either naked (non-enveloped) or enveloped. The classification of viruses is complex and based on many factors, including type and structure of the nucleoid and capsid, the presence of an envelope, the replication cycle, and the host range. Virology: Overview) is a non‑enveloped RNA RNA Ribonucleic acid (RNA), like deoxyribonucleic acid (DNA), is a polymer of nucleotides that is essential to cellular protein synthesis. Unlike DNA, RNA is a single-stranded structure containing the sugar moiety ribose (instead of deoxyribose) and the base uracil (instead of thymine). RNA generally carries out the instructions encoded in the DNA but also executes diverse non-coding functions. RNA Types and Structure calicivirus.
• Community outbreaks (nursing homes, hospitals, cruise ships, etc.) are common. 
• Causes the most common type of adult gastroenteritis

Transmission

• The virus Virus Viruses are infectious, obligate intracellular parasites composed of a nucleic acid core surrounded by a protein capsid. Viruses can be either naked (non-enveloped) or enveloped. The classification of viruses is complex and based on many factors, including type and structure of the nucleoid and capsid, the presence of an envelope, the replication cycle, and the host range. Virology: Overview is highly virulent.
• Fecal-oral route through contaminated food, water, or contaminated surfaces
• Person‑to‑person contact
• Aerosolized

Pathogenesis

• Mechanism is not entirely understood.
• Delayed gastric emptying leads to nausea and vomiting.
• Jejunal biopsy shows blunting of microvilli, but the mucosa is otherwise intact.
• Cytoplasmic vacuolization is seen along with mononuclear infiltrates of tissue.
• The virus Virus Viruses are infectious, obligate intracellular parasites composed of a nucleic acid core surrounded by a protein capsid. Viruses can be either naked (non-enveloped) or enveloped. The classification of viruses is complex and based on many factors, including type and structure of the nucleoid and capsid, the presence of an envelope, the replication cycle, and the host range. Virology: Overview appears to decrease brush border enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body's constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes, causing malabsorption Malabsorption Malabsorption involves many disorders in which there is an inability of the gut to absorb nutrients from dietary intake, potentially including water and/or electrolytes. A closely related term, maldigestion is the inability to break down large molecules of food into their smaller constituents. Malabsorption and maldigestion can affect macronutrients (fats, proteins, and carbohydrates), micronutrients (vitamins and minerals), or both. Malabsorption and Maldigestion.

Clinical presentation

• Incubation period is 24–60 hours.
• Abrupt onset of nausea and vomiting
• Watery, non-bloody diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
• Abdominal cramps
• Headache
• Myalgias
• Malaise

Diagnosis and management

• Diagnosis is usually based on clinical suspicion.
• Management includes rehydration with oral or IV fluids.