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Bacterial diarrhea


Patients present acutely with nausea, vomiting, and bloody or nonbloody diarrhea.11 Most Salmonella species, except S. typhi and S. paratyphi (causes of typhoid fever), are acquired through poultry and livestock.3,13 Proof of spread of nontyphoidal salmonellosis from person to person spread has remained elusive, despite the small infective dose.13 All serotypes of Salmonella are pathogenic to humans and appear to have the greatest effect on infants and the elderly.11


Infectious diarrhea due to Campylobacter species is similar to nontyphoidal salmonellosis.13 Campylobacter is an important cause of dysentery but can also cause nonbloody diarrhea.11 Campylobacter infection is associated with undercooked poultry11 but can also be acquired from sources such as meat, dairy, and contaminated water.13 A solid person-to-person link has yet to be established.13 Rarely, Campylobacter is a cause of Guillain-Barré syndrome.11 A clue in the history, such as diet, environmental exposure, or ascending weakness/paralysis, may be useful in diagnosing infection caused by Campylobacter species.


Shigellosis often presents with bloody diarrhea. Because Shigella is found in the stool of infected patients and is highly contagious with a small infective dose, shigellosis is commonly associated with outbreaks, especially in young children.3,13 Therefore, day care centers and families are particularly vulnerable. Secondary cases are frequently related to contact with sick individuals.13 Shigella dysenteriae is a particularly virulent strain that produces Shiga toxin (causing hemolytic uremic syndrome [HUS]), and infection with this organism has close to 10% fatality rates in certain regions of the world.11 Clues to the diagnosis are dysentery in a young child, a history of outbreaks at a visited day care center or institution, and exposure to an individual with dysentery.

Escherichia coli O157:H7

Enterohemorrhagic E. coli (EHEC), also a producer of Shiga toxin, is an important cause of dysentery in the United States.11 It can cause not only severe hemorrhagic colitis but also HUS, which develops in about 6% to 8% of cases and is reported in up to 13% of children.3,13 Transmission is typically through contaminated meat, although secondary cases can occur following person-to-person contact.13 About 20% of people exposed to EHEC can be expected to develop symptoms.

Escherichia coli Non-O157:H7

Other strains of E. coli, such as enteroaggregative E. coli (EAEC) and enterotoxigenic E. coli (ETEC), although not routinely isolated, are increasingly recognized as causes of acute infectious diarrhea.8 ETEC and EAEC are commonly associated with “traveler’s” diarrhea, identified in 30% and 26% of cases, respectively.14 These agents are most commonly spread through fecally contaminated food and water.14,15 Most cases consist of watery diarrhea, are self-limited, and resolve without treatment within 3 days.13 Enteropathogenic E. coli (EPEC) and enteroinvasive E. coli (EIEC) are other strains known to cause acute diarrheal illness.11


Vibrio species are a common cause of diarrhea in developing countries through the contamination of water supplies.11 Specifically, V. cholerae causes large volume loss (“rice water” stools), necessitating aggressive rehydration strategies.11 Because of the highly infectious nature of this organism, its ability to cause outbreaks, and its potential lethality, any case of V. cholerae infection should be reported to the proper health authorities.11 Another species, V. vulnificus, is associated with the consumption of raw or undercooked seafood.


L. monocytogenes is a less common although still clinically important, cause of foodborne illness, especially in the setting of outbreaks.16 Listeria can be found in many different sources, including soil, water, food (eg, dairy, delicatessen meat products), and the feces of humans and animals.17 Listeriosis ranges from acute diarrheal illness in healthy persons to invasive disease in the immunocompromised.17 Patients commonly present with mild gastrointestinal symptoms such as nausea and watery diarrhea, fever, and even muscle and joint aches.17 Pregnant women are especially vulnerable; they are approximately 13 times more likely than the general population to have listeriosis.16 Clues to the diagnosis include gastrointestinal complaints following reports of a food outbreaks/food contamination and a flulike illness preceded by diarrhea in a pregnant woman.16


Yersinia species, most commonly Y. enterocolitica, can cause acute diarrheal illness. In addition to diarrhea, Yersinia can cause ileitis and mesenteric lymphadenitis,18 mimicking the symptoms of persistent appendicitis.2 The organisms are transmitted fecal-orally in contaminated food and water.18 Despite the availability of modern methods, identifying the sources of outbreaks of yersiniosis has proved difficult.18 A possible clue to the diagnosis is persistent right lower quadrant pain in a patient with diarrhea and a normal appendix.

Clostridium difficile

Lastly, an important form of diarrhea is antibiotic-associated diarrhea. Causing about 10% to 20% of cases, Clostridium difficile is responsible for most cases of antibiotic-associated colitis.19 The presentation can range from a mild diarrheal illness to pseudomembranous colitis, systemic illness, and sepsis.20 The most common association is recent antibiotic use with the new onset of significant diarrhea and/or abdominal pain.20 The most commonly implicated antibiotics are clindamycin, broad-spectrum penicillins, and cephalosporins, although any agent may be the cause.19 C. difficile colitis is also contagious, evidenced by its ability to spread environmentally and from person to person.13 Feared complications of C. difficile colitis range from dehydration to toxic megacolon and perforation, and the possible need for colectomy. The most commonly implicated risk factors include advanced age, recent exposure to antibiotics, and hospitalization.19 Relapses are common, with rates approaching 20% to 25% of cases following antibiotic treatment.19

Viral diarrhea

Viral diarrhea frequently presents as watery, noninvasive diarrhea of acute onset, often associated with nonspecific systemic symptoms such as low-grade fever, headache, myalgia, and incidence during the winter months. In immunocompetent adults, symptoms are usually self-limited, lasting less than 48 hours, but they may persist for longer than 1 week. Prolonged and severe illness occurs more often in young children, the elderly, and hospitalized or immunodeficient patients.

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In the developed world, viral agents should be highest on the list of differential diagnoses for acute diarrhea. Of these, Norwalk virus (Norovirus) is the most common cause of acute diarrhea in adults. Norwalk virus infection usually presents abruptly, with symptoms of nausea, vomiting, and diarrhea, after a 12- to 48-hour incubation period, although patients may present with only vomiting or diarrhea. Most cases are self-limited and last 1 to 3 days, but more prolonged illness occurs in about 10% of cases.21 Norwalk virus infection is exceptionally virulent, (only 18 virus particles are required to cause infection) and is transmitted via virus particles shed in stool and vomit. Contaminated food and drinking water commonly cause outbreaks in restaurants, cruise ships, healthcare facilities, schools, and day care facilities.21 Norwalk-like viruses in the family Caliciviridae are other strains causing infection that presents similarly to Norwalk virus infection and are responsible for more than 90% of diarrheal cases in the United States.13 Rotavirus is the most common cause of serious diarrhea in children up to 23 months of age; patients present with severe nausea and vomiting that often leads to hospitalization.11 Children usually acquire rotavirus infection from day care facilities where hygiene is not ideal.13 Immunity to rotavirus is typically acquired by the age of 2 years, so infection is less common in older children and adults22; however, 15% to 33% of adults in families with children infected with rotavirus may acquire a mild infection.13 Other viral pathogens responsible for acute diarrhea include adenovirus, astrovirus, calicivirus, enterovirus, and coronavirus.10 In the case of virally acquired diarrheas, diagnosing the specific species is often not of great clinical concern because the treatment and management are usually the same: rehydration, electrolyte repletion, and symptomatic management.