In this chapter, diarrhea is defined as an increase in frequency, fluidity, or volume of bowel movements relative to the usual habit for a person. Acute diarrhea is second in frequency only to acute respiratory tract disease in American families. Severe, acute diarrhea is more prevalent in vulnerable groups such as the elderly, travelers, those immunosuppressed from human immunodeficiency virus (HIV), those taking steroids, and those undergoing chemotherapy. Diarrhea most frequently results from acute gastroenteritis caused by a virus or (less often) by bacteria or protozoa.
Infectious diarrhea is more prevalent in patients with close living (including shipboard) or working conditions and who are exposed to contaminated food and water or inadequate sewage disposal. Other common causes of diarrhea are irritable bowel syndrome (IBS) (previously called irritable colon, mucous colitis, or functional diarrhea), diabetes, and ingestion of antibiotics, anti-inflammatory agents, magnesium-containing substances, alcohol, lactose intolerance, and celiac disease (gluten sensitivity). The diarrhea of IBS, diabetes, lactose intolerance, continuous drug ingestion, or alcoholism is usually chronic.
In all age groups, viral gastroenteritis is the most common cause of acute diarrhea. This is usually a benign, self-limiting condition in adults but can result in severe dehydration in infants and children. In infants younger than 3 years, rotavirus is responsible for about 50% of wintertime nonbacterial gastroenteritis. This winter peak is even greater in temperate climates, such as that found in the United States. Salmonella as a cause of gastroenteritis is more common in children ages 1 to 4 years. Epidemics of Shigella have been noted in children ages 1 to 4 years and in people living in closed environments, particularly those with substandard sanitation (e.g., in prisons and custodial institutions).
Giardiasis is not common in children, but infants are susceptible. Infants may be quite ill, in contrast to adults, who are often asymptomatic. However, acute or subacute diarrhea with marked symptomatology may also occur in some adults with giardiasis. Reports of symptomatic giardiasis have increased, primarily among hikers and campers, who are most likely to drink Giardia-infested water.
Whenever diarrhea in infants less than 1 year of age corresponds to increased ingestion of dairy products, lactose intolerance (lactase deficiency) should be suspected. This form of diarrhea is not limited to infants and young children. It occurs in 15% of persons of northern European descent, up to 80% of African Americans and Hispanics, and up to 100% of Native Americans and Asians. Although these people may not have previously demonstrated lactose intolerance, lactase production normally decreases with age. This decrease is more pronounced in some people, and diarrhea seems to follow acute or chronic ingestion of large quantities of lactose as found in milk, cheese, ice cream, and other dairy products. Transient lactase deficiency is common after infectious gastroenteritis.
Middle-aged women with chronic diarrhea are more likely to have functional diarrhea or irritable bowel syndrome. This condition seems to have a predilection for young women who are raising children, especially if they have the added responsibility of a job outside the home. It affects other stressed people as well. Another form of diarrhea reported to be more frequent among middle-aged women is that due to the misuse or surreptitious use of purgatives. Patients who use laxatives surreptitiously often demonstrate other features of hysterical behavior. The addition of sodium hydroxide to the stool provides a simple test for some forms of laxative abuse. The over-the-counter laxative products Ex-Lax, Feen-A-Mint, and Correctol contain phenolphthalein, which turns the stool red when alkali (sodium hydroxide) is added.
Patients with diabetes and associated neurologic dysfunction may also have chronic diarrhea. Some diabetic patients have gastric stasis and poor bowel motility, permitting bacterial overgrowth in the small bowel, which may produce uncontrollable, explosive, postprandial diarrhea. Patients with this condition may refrain from eating before leaving their homes to avoid uncontrollable diarrhea at an inconvenient time. A therapeutic trial of antibiotics may stop the diarrhea by combating the bacterial overgrowth.
Although acute diarrhea is usually benign and self-limiting, the following patients are particularly prone to serious complications from acute and chronic diarrhea: neonates, elderly people, patients with sickle cell disease, and those who are immunocompromised (by underlying disease or chemotherapy). Diarrhea due to enteric infections from protozoal, fungal, bacterial, and viral pathogens is common in patients with acquired immunodeficiency syndrome (AIDS).
It is important to note the onset and duration of symptoms, weight loss, nocturnal diarrhea, and whether contacts are sick. A useful approach to the differential diagnosis of diarrhea is to separate acute diarrhea (which has an abrupt onset; lasts for less than 1 week; and may be associated with a viral prodrome, nausea, vomiting, or fever) from chronic diarrhea (in which the initial episode lasts longer than 2 weeks or symptoms recur over months or years). The acute onset of diarrhea in a previously healthy patient without signs or symptoms of other organ system involvement suggests an infectious cause that most often is viral. Norwalk virus has caused outbreaks of diarrhea among travelers on cruises. When vomiting and diarrhea begin suddenly and occur in many people at the same time, a preformed bacterial toxin (e.g., staphylococcal enterotoxin) is often the cause. Symptoms usually begin 2 to 8 hours after ingestion of contaminated food, most often in the summer months, when food may be inadequately refrigerated. With Salmonella, Shigella, or Campylobacter, symptoms are delayed for 24 to 72 hours while the organisms multiply in the body. With Giardia this delay may be 1 to 2 weeks.
Chronic diarrhea is most commonly caused by IBS, medications, dietary factors, chronic inflammatory bowel disease, and colon cancer. IBS may manifest as chronic or intermittent diarrhea (which classically alternates with constipation) or as flare-ups of diarrhea that occur during stressful periods. Stools are looser and more frequent with the onset of pain. A history of hard, often marble-like stools alternating with soft bowel movements, especially if associated with mucus in the toilet bowl or on the surface of the stool, suggests IBS. Although a patient suffers from chronic IBS, a superimposed case of viral gastroenteritis, salmonellosis, or giardiasis must still be considered. In such patients, a new cause of diarrhea should be sought if the usual diarrhea associated with the irritable colon changes or exacerbates.
Persistent diarrhea with frothy, foul-smelling stools that sometimes float suggests a pancreatic or small-bowel cause. Foul-smelling, watery, explosive diarrhea with mucus is often seen in giardiasis. The latency period may be 1 to 3 weeks. The onset of diarrhea due to giardiasis may be acute or gradual; it may persist for several weeks or months.
Functional diarrhea almost never occurs at night and seldom awakens the patient. It is typically present in the morning. Copious amounts of mucus may be present, but blood is seldom in the stool except that from hemorrhoidal bleeding. If questioned, the patient may admit to noticing undigested food in the stool and rectal urgency. Nocturnal diarrhea almost always has an organic cause.
It is also diagnostically helpful to classify acute diarrhea into two types: toxin-mediated diarrhea (small-bowel diarrhea) and infectious diarrhea (colonic diarrhea) (Table 10-1). Patients with toxin-mediated diarrhea have an abrupt onset (often a few hours after eating potentially contaminated foods, especially unpasteurized dairy products and undercooked meat or fish) of large-volume, watery diarrhea associated with variable nausea, vomiting, increased salivation, crampy abdominal pain, and general malaise but little or no fever. The onset of neurologic symptoms in association with diarrhea suggests Clostridium toxin (botulism).