Infectious Diarrhea

Clinical Presentation: Every year throughout the world more than 5 million people-most of them kids younger than 1 year-die of acute infectious looseness of the bowels. Although death is really a uncommon outcome of infectious diarrhea within the United States, morbidity is substantial.

It is estimated that you will find more than 200 million episodes each year, resulting in 1.8 million hospitalizations at a price of $6 billion per year. The morbidity and mortality attributable to diarrhea are largely due to loss of intravascular volume and electrolytes, with resultant cardiovascular failure. For example, adults with cholera can excrete a lot more than 1 L of fluid per hour.

Contrast this with the typical volume of fluid lost daily within the stools (150 mL), and it is clear why massive fluid losses connected with infectious diarrhea can lead to dehydration, cardiovascular collapse, and death. Gastrointestinal (GI) tract infections can present with primarily upper tract symptoms (nausea, vomiting, crampy epigastric pain), small intestine symptoms (profuse watery diarrhea), or large intestine signs or symptoms (tenesmus, fecal urgency, bloody looseness of the bowels).

Sources of infection consist of person-to-person transmission (fecal-oral spread of Shigella), water-borne transmission (Cryptosporidium), food-borne transmission (Salmonella or S aureus foods poisoning), and overgrowth following antibiotic administration (Clostridium difficile).

Etiology: A wide range of viruses, bacteria, fungi, and protozoa can infect the GI tract. However, in the majority of instances, symptoms are self-limited, and diagnostic evaluation isn't performed. Individuals presenting to medical attention are biased toward the subset with more severe signs or symptoms (eg, high fevers or hypotension), immunocompromise (eg, HIV or neutropenia), or prolonged duration (eg, chronic diarrhea defined as lasting 14 days). An exception is large outbreaks of food-borne sickness, in which epidemiologic investigations may detect individuals with milder variants of illness.

Pathogenesis: A comprehensive approach to GI tract infections starts using the classic host-agent-environment interaction model. A quantity of host elements influence GI tract infections. Individuals at extremes of age and with comorbid conditions (eg, HIV infection) are at higher risk for symptomatic infection.

Medications that alter the GI microenvironment or destroy typical bacterial flora (eg, antacids or antibiotics) also predispose individuals to infection. Microbial agents responsible for GI sickness could be categorized according to kind of organism (bacterial, viral, protozoal), propensity to attach to various anatomic sites (stomach, little bowel, colon), and pathogenesis (enterotoxigenic, cytotoxigenic, enteroinvasive).

Environmental elements can be divided into three broad categories based on mode of transmission: (1) water borne, (2) foods borne, and (three) individual to person. GI tract infections can involve the stomach, leading to nausea and vomiting, or affect the small and large bowel, with looseness of the bowels as the predominant symptom.

The term "gastroenteritis" classically denotes infection of the stomach and proximal little bowel. Organisms causing this disorder consist of Bacillus cereus, S aureus, and a quantity of viruses (rotavirus, norovirus). B cereus and S aureus produce a preformed neurotoxin that, even in the absence of viable bacteria, is capable of causing disease, and these toxins represent major leads to of foods poisoning.

Although the exact mechanisms are poorly understood, it's thought that neurotoxins act locally, through stimulation of the sympathetic nervous system having a resultant improve in peristaltic activity, and centrally, through activation of emetic centers within the brain. The spectrum of diarrheal infections is typified by the diverse clinical manifestations and mechanisms via which E coli can trigger diarrhea.

Colonization from the human GI tract by E coli is universal, usually occurring within hours following birth. Nevertheless, when the host organism is exposed to pathogenic strains of E coli not normally present in the bowel flora, localized GI illness or even systemic sickness may occur.

You will find five major classes of diarrheogenic E coli: enterotoxigenic (ETEC), enteropathogenic (EPEC), enterohemorrhagic (EHEC), enteroaggregative (EAEC), and enteroinvasive (EIEC). Functions typical to all pathogenic E coli are evasion of host defenses, colonization of intestinal mucosa, and multiplication with host cell injury.

This organism, like all GI pathogens, should survive transit via the acidic gastric environment and be able to persist within the GI tract despite the mechanical force of peristalsis and competition for scarce nutrients from existing bacterial flora. Adherence can be nonspecific (at any part from the intestinal tract) or, a lot more commonly, particular, with attachment occurring at well-defined anatomic areas.

Once colonization and multiplication happen, the stage is set for host injury. Infectious diarrhea is clinically differentiated into secretory, inflammatory, and hemorrhagic kinds, with different pathophysiologic mechanisms accounting for these diverse presentations. Secretory (watery) diarrhea is caused by a quantity of bacteria (eg, Vibrio cholerae, ETEC, EAggEC), viruses (rotavirus, norovirus), and protozoa (Giardia, Cryptosporidium).

These organisms attach superficially to enterocytes in the lumen of the small bowel. Stool examination is notable for the absence of fecal leukocytes, even though in uncommon instances there's occult blood in the stools. Some of these pathogens elaborate enterotoxins, proteins that improve intestinal cyclic adenosine monophosphate (cAMP) production, primary to net fluid secretion. The classic example is cholera.

The bacterium V cholerae creates cholera toxin, which leads to prolonged activation of epithelial adenylyl cyclase within the small bowel, primary to secretion of massive amounts of fluid and electrolytes into the intestinal lumen. Clinically, the patient presents with copious diarrhea ("rice-water stools"), progressing to dehydration and vascular collapse without having vigorous volume resuscitation.

ETEC, a common trigger of acute diarrheal sickness in young kids and the most typical trigger of looseness of the bowels in travelers returning to the United States from developing countries, creates two enterotoxins. The heat-labile toxin (LT) activates adenylyl cyclase in a manner analogous to cholera toxin, whereas the heat-stable toxin (ST) activates guanylyl cyclase activity.

Inflammatory diarrhea is really a result of bacterial invasion of the mucosal lumen, with resultant cell death. Patients with this syndrome are usually febrile, with complaints of crampy lower abdominal discomfort as nicely as diarrhea, which might contain visible mucous. The term dysentery is utilized when there are substantial numbers of fecal leukocytes and gross blood.

Pathogens connected with inflammatory looseness of the bowels consist of EIEC, Shigella, Salmonella, Campylobacter, and Entamoeba histolytica. Shigella, the prototypical trigger of bacillary dysentery, invades the enterocyte through formation of an endoplasmic vacuole, which is lysed intracellularly. Bacteria then proliferate within the cytoplasm and invade adjacent epithelial cells.

Production of a cytotoxin, the Shiga toxin, leads to local cell destruction and death. EIEC resembles Shigella both clinically and with respect towards the mechanism of invasion of the enterocyte wall; however, the specific cytotoxin associated with EIEC has not yet been identified. Hemorrhagic diarrhea, a variant of inflammatory diarrhea, is primarily triggered by EHEC.

Infection with E coli O157:H7 has been connected with a quantity of deaths from the hemolytic-uremic syndrome, with a number of well-publicized outbreaks related to contaminated foods. EHEC leads to a broad spectrum of clinical disease, with manifestations including (1) asymptomatic infection, (2) watery (nonbloody) looseness of the bowels, (three) hemorrhagic colitis (bloody, noninflammatory diarrhea), and (4) hemolytic-uremic syndrome (an acute illness, primarily of children, characterized by anemia and renal failure). EHEC doesn't invade enterocytes; nevertheless, it does create two Shiga-like toxins (Stx1 and Stx2) that closely resemble the Shiga toxin in structure and function. After binding of EHEC towards the cell surface receptor, the A subunit of the Shiga toxin catalyzes the destructive cleavage of ribosomal RNA and halts protein synthesis, leading to cell death.

Clinical Manifestations: Clinical manifestations of GI infections vary depending on the on website of involvement For instance, in staphylococcal foods poisoning, symptoms develop several hours after ingestion of foods contaminated with neurotoxin-producing S aureus. The symptoms of staphylococcal food poisoning are profuse vomiting, nausea, and abdominal cramps.

Diarrhea is variably present with agents leading to gastroenteritis. Profuse watery (noninflammatory, nonbloody) diarrhea is connected with bacteria that have infected the small intestine and elaborated an enterotoxin (eg, Clostridium perfringens, V cholerae). In contrast, colitis-like symptoms (lower abdominal pain, tenesmus, fecal urgency) and an inflammatory or bloody diarrhea occur with bacteria that more generally infect the large intestine.

The incubation period is usually longer (> 3 days) for bacteria that localize towards the large intestine, and colonic mucosal invasion can occur, causing fever, bacteremia, and systemic symptoms.