Infectious Diarrhea

Infectious Diarrhea

For all patients, assume that new-onset diarrhea has an infectious etiology. After an infectious cause is excluded, then the other possible causes can be systematically ruled out.

In general, to exclude infection, stool should be evaluated for the presence of white cells or“fecal leukocytes,” as well as culture and ova and parasite examination. Clostridium difficile toxin and stool Giardia-antigen testing are done when there are clues to these diagnoses in the history.

The most common causes of infectious diarrhea are Campylobacter and Salmonella, especially in patients with sickle cell and achlorhydria. One can only make a definitive determination of the etiology with a stool culture.

Note

As initial steps in management for diarrhea, determining when to admit the patient

and when to use intravenous fluids and antibiotics are more important than determining the precise causative agent.

Clinical presentation

Table 4-1. Clues to the Diagnosis of Infectious Diarrhea Prior to Results of Culture

Causative Agent	Patient Symptoms or History	Additional Comments
Bacillus cereus	Ingestion of refried Chinese food and the spores from Bacillus that it contains. Vomiting is prominent. Blood is never present.	Short incubation period (1–6 hours)
Campylobacter	Reactive arthritis, Guillain-Barré syndrome	Most common cause of bacterial gastroenteritis
Cryptosporidia, Isospora	Found in HIV-positive patients with <100/mm3 CD4 cells	—
E. coli 0157:H7	Associated with the ingestion of contaminated hamburger meat. The organism can release a Shiga toxin, provoking hemolytic uremic syndrome.	Hemolytic uremic syndrome happens when the organism dies; that is why antibiotics are contraindicated. Platelet transfusions are also contraindicated, even if the platelet count is low because the new platelets may only make it worse.
Giardia	The ingestion of unfiltered water, as on a camping trip or in the mountains, or in drinking fresh lake water. Giardia never gives blood in the stool. There is abdominal fullness, bloating, and gas.	Giardia can also simulate celiac disease in terms of causing fat and vitamin malabsorption if it is not eradicated.
Salmonella	Ingestion of chicken and eggs, dairy products	—
Scombroid	Patients who ingest contaminated fish experience vomiting, diarrhea, flushing, and wheezing within minutes of eating it.	Organisms invade, producing and then releasing histamine into the flesh of fish, such as tuna, mahi mahi, and mackerel.
Shigella, Yersinia	No clues strong enough to point to the etiology until the results of the stool culture are known.	Yersinia can mimic appendicitis. Also common in people with iron overload, e.g., hemochromatosis.
Vibrio parahaemolyticus	Ingestion of raw shellfish, such as mussels, oysters, and clams	Typically presents as severe systemic gastroenteritis in patients with underlying disease (esp. chronic liver disease)
Vibrio vulnificus	Also in raw shellfish, but has a particularly high incidence in people with underlying liver disease or disorders of iron metabolism. Also associated with the development of skin bullae.	Typically presents as severe systemic gastroenteritis in patients with underlying disease (esp. chronic liver disease)
Viral	Children in day-care centers; the absence of blood and white cells	No systemic manifestation
Staphylococcus  aureus	Ingestion of dairy products, eggs, salads. Upper GI symptoms (nausea/vomiting) predominate; rarely diarrhea.	Short incubation period (1–6 hours)
Ciguatera-toxin	2–6 hours after ingestion of large reef fish (grouper, red snapper, and  barracuda). Also neurological symptoms → paresthesia, weakness, and reversal of heat and cold.	—

Diagnosis. Stool for fecal leukocytes is the most useful test that can be done immediately. Fecal leukocytes are only found when there has been invasion of the intestinal mucosa, as in dysen- tery, which is a bacterial infection of the bowel, producing diarrhea and bloody stool.

Invasive organisms need 24 to 36 hours to produce their effect and never give blood in the stool within the first few hours of their ingestion. (The only exception is the protozoan Entamoeba histolytica, which can give blood or white cells in stools.) The invasive organisms are Salmonella, Shigella, Campylobacter, Vibrio parahaemolyticus, Yersinia, Escherichia coli, and Vibrio vulnificus (think people drinking sea water). The most definitive test for these bacterial organisms is a      stool  culture.

Cryptosporidiosis is diagnosed with a unique test, a modified acid-fast test. The routine ova and parasite examination does not reliably detect cryptosporidiosis.

Giardia is best diagnosed with an ELISA stool antigen test. A single stool antigen test has 90% sensitivity. Three stool ova and parasite examinations have only 80% sensitivity.

Treatment. Most cases of food poisoning and infectious diarrhea will resolve spontaneously and will not need specific antimicrobial therapy. Even when they cause severe disease, as defined by high-volume stools with dehydration, antibiotics generally do not help. Antibiotics are used if there is abdominal pain, blood in the stool, and fever. The decision to use antibiotics is always made prior to knowing the result of the stool culture, so the treatment is always empiric and then modified when the culture results are known. The best empiric therapy for infectious diar- rhea is ciprofloxacin or the other fluoroquinolones ± metronidazole.

Scombroid poisoning is treated with antihistamines, such as diphenhydramine. Giardia is still treated primarily with metronidazole. A newer agent for Giardia is tinidazole, which is effective in a single dose. Cryptosporidiosis is treated with nitazoxanide, although it has limited efficacy. The truly effective therapy for cryptosporidiosis is to raise the CD4 count to >100/mm3 with antiretrovirals. Nitazoxanide is superior to paromomycin for  cryptosporidium.

There is no specific therapy for viral diarrhea. Patients are managed with fluid and electrolyte support until the infection resolves.