Pay attention to clues when diagnosing diarrhea

December 2005

Although most diarrheal cases among children are frequent and uncomplicated, some will require intervention or further investigation of epidemiological factors.

“Diarrhea can be difficult, it is common, but occasionally can be difficult. Pay attention to clues that suggest a more complicated picture,” said James P. Nataro, MD, PhD, at the 18th Annual Infectious Diseases in Children Symposium, held in New York. Such clues include persistent or bloody diarrhea, or if it occurs in an immunocompromised host or a returning traveler, according to Nataro, professor of pediatrics at the University of Maryland School of Medicine, Baltimore.

“We know that diarrhea is a common manifestation of intestinal disease and extra-intestinal disease,” he said. “For example, diarrhea is the most common presentation of urinary tract infections [UTI] in children under 4 years of age and is sometimes associated with otitis media [OM], pneumonia and viral syndromes, so the take home message here is don’t be overly focused on the diarrhea in someone who comes in if they are systemically ill.”

Nataro reviewed indications for workup of patients with diarrheal disease, and highlighted cases and indications as to when diarrhea can be difficult.

When diarrhea is difficult

Persistent diarrhea is defined as lasting 14 days or longer. Differential diagnoses include parasites, such as Giardia, Entamoeba, and amebae; bacterial pathogens, such as Salmonella, Shigella, Yersinia, Campylobacter, and various types of E. coli. Occasionally some viruses cause brief diarrhea and some cause a syndrome of post-infectious malabsorption or persistent non-infectious diarrhea, according to Nataro, also an Infectious Diseases in Children editorial board member.

The workup of persistent diarrhea includes the stool ova and parasites, a stool culture and a lactose-free diet; monitor the patient’s weight and take a history for preexisting syndromes or underlying disease.

Immunodeficiency is an important underlying cause of persistent diarrhea. Nataro recommended pediatricians ask the following questions: has the child grown well, has there been persistent, recurrent infections like OM, sinusitis, pneumonia and recurring invasive bacterial infections and has there been adverse reactions to live attenuated vaccines? Pediatricians should also consider the possibility of HIV in addition to congenital deficiencies of antibodies and T-cells.

Other syndromes associated with persistent diarrhea include celiac diseases, congenital syndromes, pancreatitis, cystic fibrosis, and toddler’s diarrhea, which should be a diagnosis of exclusion, according to Nataro.

Blood in stools can occur with any invasive inflammatory pathogen, specifically Shigella, Salmonella, Campylobacter and Yersinia. Shiga toxin-producing E. coli (STEC) is a classical cause of afebrile bloody colitis. Patients may also have fecal white blood cells, as well as pus and mucous, with systemic evidence of inflammation. STEC is a highly communicable pathogen that is most common in Northern tier states and is transmitted in beef products, or articles contaminated with manure. If STEC is suspected, particularly on the basis of bloody stools, request that STEC be sought in stool culture. Other steps that pediatricians can take when STEC is suspected is to ensure that the patient remains hydrated, to withhold antibiotics, to maintain good household hygiene, to look for other related cases and to report positive cases to the state health department. Pediatricians should watch for hemolytic uremic syndrome, the triad of renal failure, anemia, and thrombocytopenia.

“You may pick up the early triad in a contact of someone you identify with the E. coli, an additional reason why you really need to think about the family situation of these cases,” he said.

The latest data suggest the most common cause of traveler’s diarrhea are two different pathotypes of E. coli — enterotoxigenic E. coli (ETEC) and enteroaggregative E. coli (EAEC) – and Shigella species. Most cases resolve before they present to the physician, in particular ETEC and viral causes of traveler’s diarrhea are brief and self-limiting.

“If the cases are persistent think about the potential for parasites, bacteria and post-infectious malabsorption,” he said. “Giardia, E. histolytica, Cryptosporidium and Cyclospora are other possibilities and can be somewhat complicated.”

Dientamoeba fragilis and Blastocystis hominis are organisms of low virulence and are usually considered non-pathogenic. Nataro recommended treating the patient shedding one of these ameba with Flagyl (Searle) if there is no other pathogen; and if there is no response to emperic therapy, it is most likely not due to an ameba and the pediatrician should refer the patient to a gastroenterologist.

There are six different pathotypes of diarrheagenic E. coli. The more common ones seen in persistent diarrhea are enteropathogenic E. coli (EPEC), which typically occurs only in returning travelers, and EAEC, which has no limitations to age and locale. Two recent studies suggest that between 5% and 10% of diarrhea is due to EAEC. Different pathoypes and what physicians and pediatricians need to know about diagnostic and treatment recommendations are described in the Red Book, according to Nataro.

Sending a stool culture

“In an era of managed care, stool cultures are expensive and will be looked at closely,” he said. “Data can guide physicians in the decision of when to send a stool culture.”

Literature suggests the following indications call for a culture: fever, severe abdominal pain, diarrhea starts before vomiting, more than three stools pass per day, presence of blood or pus, and fecal leukocytes. If the patient cannot shed a stool in the office and a diaper can’t be sent, recommendations suggest specimen collection via rectal swab, although the yield for detection of the pathogen is somewhat lower. For example, a single stool culture’s yield varies from 70% to 90% depending on the pathogen and a swab’s yield varies from 50% to 70%.

Antibiotics are not indicated for most of these bacterial pathogens. Only Shigella has a strong indication for antibiotic therapy because it shortens the duration and severity and decreases the excretion. Researchers found that in the United States, Shigella is increasingly resistant to sulfamethoxazole-trimethoprim and azithromycin (zithromax, Pfizer). Azithromycin ameliorates Campylobacter if treated early in the illness, he said.

Pediatricians should also be alert to risks like travel, antibiotic administration, household contacts and seafood ingestion.

For more information:

• Nataro JP. When diarrhea is difficult. Presented at the 18th Annual Infectious Diseases in Children Symposium. Nov. 19-20, 2005. New York City.