Acute diarrhea overview

# Overview
The term 'diarrhea' is derived from the Greek term "to flow through." It is characterized by the passage of unformed or abnormally liquid stools at an increased frequency. Acute diarrhea has a duration of 7 days, in moderate-to-severe cases, dysentery, and to determine etiology in order to enable directed pathogen-specific therapy. Symptomatic treatment for diarrhea includes consumption of adequate amounts of water, mixed with electrolytes to replace water and salt depletion. According to the ACG Clinical Guideline, use of balanced electrolyte rehydration is recommended in patients with travellers diarrhea, excessively watery and severe diarrhea. Medical supervision is required in infants with diarrhea, moderate or severe diarrhea in young children, bloody diarrhea, diarrhea for more than two weeks and diarrhea associated with non-cramping abdominal pain, fever and weight loss. Empiric therapy is used as an initial treatment for diagnostic testing, after testing has failed to confirm a diagnosis, when there is no specific treatment or when specific treatment fails to effect a cure. Pharmacotherapy for acute diarrhea includes the use of antibiotics, anticholinergics, antimotility agents and other nonspecific antidiarrheal agents (probiotics).

# Historical Perspective
The word "diarrhea" was coined by Hippocrates. 'Diarrhea' is derived from the Greek term "to flow through." Diarrhea is a common manifestation of the gastrointestinal disease.

# Classification
Diarrhea is defined as the passage of unformed or abnormally liquid stools at an increased frequency. Acute diarrhea has a duration of <2 weeks and may be classified on the basis of etiology and presentation. On the basis of etiology, acute diarrhea may be classified into infectious and non-infectious subtypes. Based on the type of presentation, acute diarrhea may be classified into watery and inflammatory types. Watery diarrhea may further be classified into secretory and osmotic types of diarrhea.

# Pathophysiology
Diarrhea is a condition of altered intestinal water and electrolyte transport. The pathophysiology of acute diarrhea includes osmotic, secretory, inflammatory types, and diarrhea due to altered motility. Acute diarrhea due to an osmotic causes includes osmotic laxatives such as lactose intolerance, antacids, fructose, lactulose, laxatives magnesium, phosphate, and sorbitol, which induce a secretory state. Bacterial infection of the intestine leads to activation of epithelial ion channels with increased secretion of anions. Invasion of the epithelium by various pathogens lead to exotoxin production and enhancement of enterocyte secretion by cytotoxins or intracellular signalling. In case of motility disorders of the gut, rapid transit time delivers fluid secreted during digestion to the distal small bowel or colon. This prevents reabsorption of normally secreted fluid in the small bowel, overwhelming the reabsorptive capacity of the colon.

# Causes
Common causes of acute diarrhea in both developing and developed nations are infections. Infectious agents responsible for majority of cases include Norovirus, Salmonella, Shigella, Clostridium perfringens, Staphylococcus aureus, Rotavirus, Shigella, Enterotoxigenic E.coli (ETEC), Campylobacter and Cryptosporidium parvum. Less commonly, acute diarrhea may be be caused by Norwalk viruses or may be associated with systemic infections including influenza, urinary tract infections, and HIV infection. Other common causes of acute diarrhea include food allergies and drug side effects. Less commonly, acute diarrhea can be a symptom in the initial stages of systemic conditions including Ischemic colitis, Hyperthyroidism, Tropical sprue and with disorders of digestion and the absorption process.

# Differentiating Acute Diarrhea from Other Diseases
The differentials of acute diarrhea include Ischemic colitis, Lactose intolerance, Tropical sprue, Pseudomembranous enterocolitis, Campylobacteriosis, Salmonellosis, Shigellosis, Escherichia coli enteritis, Yersinia enterocolitica, Vibrio cholera, Aeromonas, Plesiomonas, Staphylococcus aureus, Bacillus cereus, Clostridium perfringens, Rotavirus, Norovirus, Adenovirus, Entamoeba histolytica, medications, Short bowel syndrome, Organophosphate poisoning, Radiation enteritis and Opium withdrawal.

# Epidemiology and Demographics
In the US, the overall weighted prevalence for acute diarrheal illness corresponded to 06 episodes per person per year from 1996 to 2003. It has been found that approximately 179 million cases of acute gastroenteritis including 47.8 million cases of food-borne illness, occur each year in the US. The mortality rate due to acute diarrhea has been estimated for all ages to be 17.8 deaths per 100 000 of population. Global mortality rate for children (<5 years) is much higher, with a figure of 743 deaths per 100 000 of population. Morbidity and mortality of diarrhea differs by location, with the highest rates of under-5 mortality noted in sub-Saharan Africa and South Asia, in particular in Chad (594 deaths per 100 000) and Niger (485 deaths per 100 000).

# Risk Factors
The risk factors of acute diarrhea may be assessed based on the epidemiologic associations and the patient exposure histories. Risk factors may be classified based on travel history, epidemics, outbreaks, food history, animal contact, hospitalization and immunosupression. The 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea lists the risk factors of diarrhea along with their causative pathogens.

# Screening
There is insufficient evidence to recommend routine screening for acute diarrhea.

# Natural History, Complications, and Prognosis
Untreated cases of acute diarrhea may progress to develop symptoms of fluid depletion including altered mental status, electrolyte imbalances, dehydration, metabolic acidosis and malnutrition. Common complications of acute diarrhea include confusion, convulsions, sepsis, and death. Prognosis is generally good when the underlying cause is identified and treated early.

# Diagnosis

## Diagnostic Criteria
There is no established diagnostic study of choice for acute diarrhea as it is generally self-limited. Specific diagnostic studies are performed if symptoms last >7 days, in moderate-to-severe cases, dysentery, and to determine etiology in order to enable directed pathogen-specific therapy.

## History and Symptoms
The hallmark of acute diarrhea is the sudden onset of 3 or more stools per day, lasting less than 2 weeks. The most common symptoms of acute diarrhea include increased frequency of bowel movements, abdominal pain, elevation of body temperature, symptoms of fluid loss (dark or scant urine, excessive thirst, dizziness, fatigue).

## Physical Examination
Patients with acute diarrhea usually appear ill, dehydrated or lethargic. Common physical examination findings of acute diarrhea include hypotension and other signs of volume depletion (depressed consciousness, sunken anterior fontanel, dry mucous membranes, sunken eyes, poor skin turgor and delayed capillary refill), abdominal tenderness and distension, increased peristaltic activity (borborygmi).

## Laboratory Findings
Laboratory investigations performed in the evaluation of patients with acute diarrhea include spot stool analysis, detection of occult blood, white blood cells, stool culture, quantitative stool analysis, fecal weight, stool osmotic gap, fecal pH, fecal fat concentration and analysis for laxative abuse. According to the ACG guidelines, stool culture is done only in cases where the patient is at high risk of spreading the disease to others. Stool diagnostic studies are performed when symptoms last for >7 days, patient has dysentery or moderate-to-severe diarrhea and to determine etiology to enable directed pathogen-specific therapy. Antibiotic sensitivity testing for management of acute diarrhea is not advised.

## Electrocardiogram
There are no ECG findings associated with acute diarrhea.

## X-ray
An x-ray may be helpful in the diagnosis of some of the rare causes of acute diarrhea. Findings on an x-ray suggestive of organic causes acute diarrhea include intestinal dilation, irregular mucosal surface and increased luminal fluid.

## Ultrasound
There are no ultrasound findings associated with acute diarrhea.

## CT scan
CT scan is not routinely performed for cases of acute diarrhea. However, it may help in the detection of certain rare causes of acute diarrhea such as inflammatory bowel disease, intestinal lymphoma, carcinoid syndrome, and other neuroendocrine tumors.

## MRI
There are no MRI findings associated with acute diarrhea.

## Other Imaging Findings
There are no other imaging findings associated with acute diarrhea.

## Other Diagnostic Studies
Sigmoidoscopy and colonoscopy may help in the diagnosis of conditions such as melanosis coli due to laxative abuse, amebiasis, polyps, ulceration, Crohn's disease, and ulcerative colitis. Upper GI endoscopy and biopsy help in the diagnosis of Crohn's disease, giardiasis, intestinal lymphoma, lymphangiectasia, eosinophilic gastroenteritis, Whipple's disease, mastocytosis, abetalipoproteinemia, fungal and protozoal infections.

# Treatment

## Medical Therapy
The majority of cases of acute diarrhea are self-limited and require only supportive care. Symptomatic treatment for diarrhea includes consumption of adequate amounts of water, mixed with electrolytes to replace water and salt depletion. According to the ACG Clinical Guideline, use of balanced electrolyte rehydration is recommended in patients with travellers diarrhea, excessively watery and severe diarrhea. Medical supervision is required in infants with diarrhea, moderate or severe diarrhea in young children, bloody diarrhea, diarrhea for more than two weeks and diarrhea associated with non-cramping abdominal pain, fever and weight loss. Empiric therapy is used as an initial treatment for diagnostic testing, after testing has failed to confirm a diagnosis, when there is no specific treatment or when specific treatment fails to effect a cure. Pharmacotherapy for acute diarrhea includes the use of antibiotics, anticholinergics, antimotility agents and other nonspecific antidiarrheal agents (probiotics).

## Surgery
Surgical intervention is not recommended for the management of acute diarrhea.

## Primary Prevention
Primary prevention of acute diarrhea includes measures such as counseling in patients and their close contacts. In addition, counseling prior to travel and hand washing using alcohol-based sanitizers are other recommended practices. Hand washing is particularly important for prevention of community-acquired diarrhea outbreaks in cruise ships or institutions.

## Secondary Prevention
There are no established measures for the secondary prevention of acute diarrhea.