Infectious Diarrhea

Jonathan P. Moorman

James W. Myers

Clinically, diarrhea is defined by the passage of three or more watery stools, or one or more bloody stools, in 24 hours. Viruses account for 50% to 70% of causes of acute infectious diarrhea, bacteria 15% to 20%, and parasites 10% to 15%, and it appears that 5% to 10% of cases are of unknown etiology. Definitions of the types of diarrhea are shown in Table 22-1. Specific indications for medical evaluation include profuse watery diarrhea with dehydration; dysentery; passage of many small-volume stools containing blood and mucus; fever (temperature of 38.5°C [101.3°F] or higher); passage of six or more unformed stools every 24 hours or a duration of illness longer than 48 hours; diarrhea with severe abdominal pain in a patient older than age 50; and diarrhea in the elderly (age 70 or older) or the immunocompromised patient (AIDS, after transplantation, or receipt of cancer chemotherapy). Note: Clostridium difficile-associated diarrhea is covered in an accompanying chapter dedicated to nosocomial infection.

DIAGNOSIS

From a study at the University Hospital of Geneva, the culture positivity rate of 6.1% decreased to 2.7% when patients received antimicrobial agents (p < 0.001). The positivity rate for patients hospitalized for 3 days or fewer was 12.6%, whereas it dropped to 1.4% for patients hospitalized for longer than 3 days (p < 0.001).
Stool studies will be more useful in those patients who have a history of bloody diarrhea; have traveled to an endemic area; or have recently had antibiotics, immunosuppression, or exposure to infants in day care centers.
The bacterial enteropathogens identified by normal stool culture are Shigella, Salmonella, Campylobacter, Aeromonas, and usually Yersinia. As an alternative, a rectal swab can be placed in transport media and then cultured. Please note that some pathogens will not be detected by routine stool culture. One should alert the laboratory to look for these microbes: Escherichia coli 0157:H7 and other Shigatoxin-producing E. coli, Vibrios cholerae, other noncholera Vibrios, and possibly Yersinia.
Positive fecal leukocyte, lactoferrin, and occult blood tests lend support toward using empiric antimicrobial therapy. Conversely, when negative, they will eliminate the need for stool cultures. The most commonly identified pathogens in patients with these positive test results include Shigella, Salmonella, Campylobacter, Aeromonas, Yersinia, noncholera Vibrios, and C. difficile.
Several studies have shown that the routine ordering for ova and parasites is not cost-effective in severe acute diarrhea.
A travel history is important to help define who might benefit from such testing. Infection by Cryptosporidium, Giardia, or both, should be suspected whenever one returns from Russia; Cyclospora should be considered in travelers to Nepal; and Giardia should be suspected in persons who have recently traveled to the mountainous areas of North America. In day care centers, Giardia and Cryptosporidium are
common causes of diarrhea. Also note that homosexual males will often have positive results for Giardia and Entamoeba histolytica. See Tables 22-2 and 22-3 for information about persistent and/or parasitic causes of diarrhea.

Table 22-1 Definitions of Types of Diarrhea

Entity	Days	Comments
Diarrhea		Defined as stool weight >200 g in 24 hours. The average stool output is 100 g of stool per day.
Acute	<14
Persistent	>14
Chronic	>30
Severe		The patient will have one or more of the following: volume depletion, fever, six or more stools in 24 hours, an illness lasting longer than 48 hours, or be immunocompromised.

TREATMENT OF COMMON PATHOGENS

In all patients with diarrhea requiring medical evaluation, fluid and electrolyte therapy and alteration of the diet should be part of the management.
When nonspecific therapy is desired, loperamide is the drug of choice for most cases of diarrhea. Loperamide is the recommended agent for most cases of diarrhea because of its safety and efficacy of approximately 80%.
Diphenoxylate possesses central opiate effects, which can be problematic. The antimotility drugs should not be given to patients with moderate to severe C. difficile—related diarrhea. Bismuth subsalicylate (BSS) is the preferred agent when vomiting is the important clinical manifestation of enteric infection. BSS, however, should not be given to immunocompromised patients with diarrhea to prevent the taking of excessive doses.
In some cases of severe, refractory cases, octreotide may be effective. Consultation with a gastrointestinal (GI) specialist is advised. Table 22-4 includes information on treatment of common bacterial pathogens.

TRAVELER’S DIARRHEA

General Concerns

The most common travel disease is traveler’s diarrhea (TD), affecting between 20% and 75% of those who vacation abroad. The onset of TD usually occurs within the first week of travel but may occur at any time while traveling, and even after returning home.
The risk of TD varies according to the itinerary of the tourist. Risk also varies according to the underlying health status and age of the host, with the highest incidence occurring in small children and young adults aged 20 to 30.
Certain conditions may predispose patients to a higher risk of acquiring TD, including those with HIV and other immunocompromising conditions.

Choice of cuisine also affects a traveler’s risk. Particularly risky would be food bought from a street vendor. Higher risk foods include uncooked vegetables, salads,

unpeeled fresh fruit; and raw or undercooked meat or shellfish. Safe drinks include bottled carbonated beverages; beer or wine; and boiled or treated water. Tap water and unpasteurized milk carry an increased risk of infection.

Table 22-2 Acid-Fast Negative Protozoans

Organism	Geography	Transmission	Clinical Features	Diagnosis	Treatment
*Giardia lamblia*	Anywhere but notably acquired in St. Petersburg, and the mountainous regions in North America	Waterborne and person to person Boil drinking water, or if not possible, use halogenated water purification tablets Patients with common variable immunodeficiency or x-linked agammaglobulinemia are at increased risk of infection	1-2 weeks incubation period. The clinical spectrum of giardiasis is broad, including asymptomatic cyst passage; acute, often self-limited diarrhea; and chronic severe diarrhea with malabsorption and weight loss. In addition to diarrhea, a majority of symptomatic patients report bloating, cramping, and foul-smelling, greasy stools	Identification of cysts or motile trophozoites in stool or duodenal aspirate. Sensitivity is around to 85%-90% after three stools. Newer antigen detection assays range in sensitivity from 85%-98%	Metronidazole 250-500 t.i.d. for 1-2 weeks Tinidazole 2 g PO × one dose Paromomycin 25-30 mg/kg/day in three doses for 5-10 days Avoid milk products if there is a transient lactase deficiency
*Microsporidia, Entero-cytozoon bieneusi and Encephalitozoon (formerly Septata) intestinalis*	Diverse locations	Any immunocompromised patient presenting with persistent unexplained diarrhea. HIV	Persistent diarrhea	Calcofluor White and Uvitex stains lack specificity Polymerase chain reaction techniques hold promise for improved detection of microsporidia in stool.	Albendazole 400-800 mg PO b.i.d. for 3 or more weeks Other therapies besides albendazole under study include metronidazole, atovaquone, thalidomide, and nitazoxanide Albendazole is not effective for E. bieneusi
*E. histolytica*	Diverse locations	Fecal-oral	Persistent diarrhea	Stool studies or serologic tests. Serologic tests such as enzyme-linked immunosorbent assay and agar gel diffusion are more than 90% sensitive, but these tests often become negative within a year of initial infection	Metronidazole, 750 mg t.i.d. × 5-10 days, plus either diiodohydroxyquin, 650 mg t.i.d. × 20 days, or paromomycin, 500 mg t.i.d. × 7 days