Does Your Patient Have a Foodborne Disease?

David W.K. Acheson, MD, FRCP


April 01, 2002

In This Article

Watery Diarrhea as the Major Presenting Symptom

Many foodborne microbes cause watery diarrhea, but the presence of this symptom alone is of little help in the differential diagnosis. The presence of inflammatory cells in the stool suggests a more limited group of pathogens, as discussed in the next section. Some foodborne microbes, such as Vibrio cholerae,may cause massive watery diarrhea, but this type of foodborne illness is uncommon in the United States. C perfringens is a much more likely cause of watery diarrhea in patients in the United States. Infection typically occurs after consumption of meats, poultry, or gravy in which C perfringens spores have germinated in the food, resulting in large numbers of bacteria. Following ingestion of C perfringens, a toxin is produced that leads to watery diarrhea. Reference laboratories can test the stool or food for the toxin.

Other microbial causes of watery diarrhea include enterotoxigenic E coli (ETEC); B cereus;and many of the enteric viruses, such as rotavirus, astroviruses, enteric adenoviruses, and Norwalk-like viruses. ETEC has been the cause of outbreaks of foodborne illness in the United States,[1] including a recent one in Illinois linked to potato salad. It is also a frequent cause of traveler's diarrhea. ETEC and enteric viruses are transmitted via fecal contamination of food or water from an infected person. Prepared food is therefore at the top of the list of likely sources. There are no specific tests for ETEC in routine use. The organism looks like any other E coli on standard laboratory media. A special request should be made to the testing laboratory in suspected cases of ETEC. Diagnosis of several viruses (rotavirus, enteric adenoviruses) can be made by enzyme immunoassay.[7]

Two other foodborne pathogens that may cause predominantly watery diarrhea are Cryptosporidium parvum and Cyclospora cayetanensis.[9,10] As can be seen in Table 1, C parvum causes many diseases, but only 10% of these are considered to be foodborne. In contrast, C cayetanensis causes much less disease, but 90% of it is considered to be foodborne, according to outbreak data. C parvum has gained notoriety for causing persistent chronic diarrhea in immunocompromised patients.[11] There is no proven effective therapy. C parvum is endemic in cattle and is usually acquired by humans from contaminated water, fresh produce, unpasteurized milk, or person-to-person contact. The incubation period is typically about a week but can be as long as 28 days. This microbe is known to cause large outbreaks, the largest of which occurred in Milwaukee, Wisconsin, where around 400,000 individuals became sick as a result of contaminated water.[12]C parvum can be diagnosed by acid-fast staining of stools, immunofluorescence microscopy, or enzyme immunoassay. A recently described test is designed to screen stools simultaneously for Giardia lamblia, Entamoeba histolytica/Entamoeba dispar, and C parvum.[13]

C cayetanensis infection has been associated with consumption of imported berries, which were most likely contaminated with feces-tainted water. More recently, it has been linked with fresh basil.[14] This infection can be diagnosed by direct acid-fast microscopy of stool.[15] However, most microbiology laboratories do not routinely look for C parvum and/or C cayetanensis,so they must be specifically requested. Diagnosis of C cayetanensis is important because it is readily treatable with trimethoprim-sulfamethoxazole.