Does Your Patient Have a Foodborne Disease?

David W.K. Acheson, MD, FRCP


April 01, 2002

In This Article

Inflammatory Diarrhea as the Major Presenting Symptom

Making the diagnosis of inflammatory diarrhea requires, by definition, the presence of inflammatory cells or a marker of inflammatory cells, such as lactoferrin.[3] However, clinical clues revealed in the patient's history should increase suspicion that a foodborne microbe is causing inflammatory diarrhea. Such symptoms and signs include bloody or mucoid diarrhea, severe abdominal pain, or fever. However, these markers do not help to determine the exact microbial cause of inflammatory diarrhea. Statistically, in the context of foodborne disease, a patient with inflammatory diarrhea is far more likely to be infected with Salmonella or Campylobacter than with any other microbe; Salmonella and Campylobacter are currently the 2 most common bacterial pathogens isolated from diarrheal stools in the United States.

Although there are many types of Salmonella, they can be divided into 2 broad categories: those that cause typhoid and enteric fever and those that primarily cause gastroenteritis. Typhoidal Salmonella, such as S typhi or S paratyphi, primarily colonize humans, are transmitted via the consumption of fecally contaminated food or water, and cause a systemic illness usually with little or no diarrhea. The much broader group of nontyphoidal Salmonella occur in the intestines of other animals and are therefore acquired by consuming products contaminated with animal feces.[16] Thus, many cases of salmonellosis result from either cross-contamination or undercooking of raw meat or poultry products. The major exception to this is S enteritidis, which may be present in the ovaries of chickens, resulting in transovarian contamination of eggs as they are being formed in the chicken. Salmonella may also contaminate fresh produce, and alfalfa sprouts have recently been incriminated.[17] The incubation period for nontyphoidal Salmonella is usually 1-3 days, and diagnosis is made through routine stool culture.

Foodborne disease due to Campylobacter species was not recognized until the mid-1970s. C jejuni accounts for the vast majority of foodborne campylobacteriosis, and C coli accounts for most of the remainder.The incubation period usually ranges from 2-5 days, and poultry is a frequent source of the organism. Studies from various locations, including the United States, indicate that 70% to 80% of retail poultry is contaminated with Campylobacter,[18] thus making cross-contamination during food preparation an important hazard. Although Campylobacter is fastidious and slow-growing, it can be diagnosed using routine microbiological techniques on selective plates.

STEC is now the most frequent cause of acute renal failure in the United States.[19,20] While E coli O157:H7 is the serotype most frequently associated with human disease, more than 50 other STEC serotypes have now been associated with both diarrheal disease and hemolytic-uremic syndrome. STEC is typically found in ground beef, unpasteurized juice, and raw fruits and vegetables, including alfalfa sprouts. The incubation period ranges from about 1 day up to a week. The presentation usually begins with watery diarrhea that may become bloody.

Recent data from the United States indicate that close to 50% of STEC isolates are non-O157:H7.[21] STEC can be diagnosed using Shiga toxin-based assays, which have advantages over the more conventional sorbitol MacConkey test. However, most clinical microbiology laboratories only use sorbitol MacConkey plates to test for O157:H7 STEC (O157:H7 ferments sorbitol slowly compared with other E coli), and these plates do not detect non-O157:H7 strains and seem to be less sensitive than Shiga toxin-based tests.[22] Determining whether a patient is positive for STEC has important implications in relation to antibiotic therapy. Recent data indicate that antibiotic treatment of STEC-infected patients may increase the risk of developing hemolytic-uremic syndrome.[23,24]

Shigella only colonizes humans and some nonhuman primates; therefore, transmission of Shigella in food or water is most likely to result from fecal contamination or direct contamination from a food-handler. S sonnei or S flexneri are the 2 most common species in the United States. A variety of foodshave been implicated in the spread of Shigella, including salads (potato, tuna, shrimp, macaroni, and chicken), raw vegetables, milk and other dairy products, and poultry, as well as common-source water supplies. Diagnosis is routine in clinical microbiology laboratories.

Any patient with suspected foodborne disease who has consumed raw shellfish in the proceeding 48 hours should be cultured for Vibrio species. The most likely organism is V parahemolyticus. Most laboratories do not routinely culture for Vibrio species, so a specific request should be made. An unusual cause of foodborne disease that leads to an inflammatory diarrhea is Yersinia enterocolitica, which is typically associated with consumption of undercooked pork, unpasteurized milk, or feces-contaminated water.