The E. coli O157:H7 outbreak in Belgium, Wisconsin has sickened at least 6 kids (one who developed HUS) seems to have several well-defined epidemiological circumstances that may help the State of Wisconsin Health Department identify a source. The victims seem to all be kids, the kids all come from the same relatively small part of the town, and the kids apparently do not interact socially.
Whatever the ultimate significance of these circumstances, another highly interesting epidemiological point in the outbreak is the apparent presence of Cryptosporidium and Clostridium difficile infection among the outbreak cases.
Clostridium difficile (C. difficile) is a spore-forming, gram-positive anaerobic bacillus that produces two toxins: toxin A and toxin B. These toxins typically cause gastrointestinal disease, often with severe complications. In rare cases, C. difficile-associated disease can be fatal. Although C. difficile bacteria can be present in human intestinal tracts and cause no clinical symptoms (a condition called colonization), some individuals with C. difficile colonization are at increased risk of becoming ill. The most common risk factor for C. difficile-associated disease is exposure to antibiotics, especially those with broad-spectrum activity. Although less common, exposure to agents that suppress the immune system may also increase the risk of illness. Advanced age, severe underlying illness, gastrointestinal surgery, use of nasogastric tubes, and gastrointestinal medications (such as gastrointestinal stimulants or antacids) have also been associated with an increased risk of colonization. Most cases are acquired in hospitals or nursing homes, but an increased incidence of community–acquired C. difficile has been reported as well. Recent studies indicate that C. difficile can also be found in food products, thus raising a significant question: Can C. difficile cause foodborne illness?
Sources and Transmission
C. difficile is shed in feces. Any material, device, or surface that becomes contaminated with feces—such as toilets or bathing tubs—may serve as a reservoir for C. difficile spores. The ability of C. difficile to form spores is thought to be a key feature that enables the bacteria to persist in patients and the physical environment for long periods of time, thereby facilitating its transmission.
The spores are transferred to patients in healthcare settings mainly through the hands of healthcare personnel who have touched a contaminated surface or item. Some evidence suggests that C. difficile may be brought into healthcare environments by asymptomatic carriers—otherwise healthy individuals with no apparent symptoms. Virulent strains, which cause severe disease in populations at high risk, might also cause more frequent, severe disease in populations previously at low risk—that is, in otherwise healthy persons with little or no exposure to health-care settings or antimicrobial use. Certain emerging features of C. difficile illness, such as close-contact transmission, high recurrence rate, young patient age, bloody diarrhea, and lack of antimicrobial exposure, might indicate that the illness and its effects are changing.
C. difficile has also been linked to illness in livestock. Studies have revealed high infection rates of C. difficile among neonatal pigs. Similarly, C. difficile has been implicated as a cause of diarrhea in calves. Livestock contamination raises concerns that the bacteria may make its way into retail food products. Indeed, C. difficile has been identified in raw meat intended for pet consumption in Canada, retail ground beef in Canada, and uncooked and ready-to-eat meats in retail markets in a U.S. metropolitan area.
The incubation period from ingestion of C. difficile to the development of symptoms has not been established. Among patients taking antibiotics, symptoms can appear immediately after beginning treatment or may not develop until several weeks after it is completed.
Most often, C. difficile-associated disease includes symptoms of mild to moderate non-bloody diarrhea, sometimes accompanied by lower abdominal cramping. Systemic symptoms, such as fever, are typically absent; mild abdominal tenderness is usually the only finding on physical exam.
In more severe cases, colitis develops, with symptoms of profuse watery diarrhea and abdominal pain and distention; bloody stools are rare. Fever, nausea, and dehydration are also often present in severe cases. Furthermore, a characteristic membrane with adherent yellow plaques can be found in the colon. Patients with severe colitis are at increased risk of developing paralytic ileus (blocked colon due to lack of peristalsis―the normal rhythmic contraction of the colon muscles) and toxic megacolon (dilated colon). These conditions may lead to a decrease in diarrhea. Severe cases may also include fulminant colitis―a rapid downhill clinical course that occurs among 1% to 3% of patients. Patients may have an acute abdomen and systemic symptoms, such as fever and tachycardia, and may require surgery.
Mortality rates associated with C. difficile-related disease in the U.S. increased nearly three-fold from 1999 to 2002. A recent study, which included C. difficile-related cases where C. difficile infection was present but not listed as the underlying cause of death, demonstrated an increase in deaths from 5.7 per million population in 1999 to 23.7 per million in 2004. It is possible that the increased rates were due to the emergence of a highly virulent strain of C. difficile.
Stool cultures are the most sensitive means available to detect C. difficile, however, they are also the test most often associated with false-positive results, due to presence of non-toxigenic bacterial strains. C. difficile stool cultures are also labor intensive and require the appropriate culture environment to grow anaerobic microorganisms. Results are available within 48 to 96 hours of the test.
Antigen detection tests for C. difficile have a very fast turn around time (less than one hour); these tests detect the presence of C. difficile antigen by latex agglutination or immunochromatographic assays. Antigen tests must be combined with toxin testing to verify diagnosis. One type of antigen test, enzyme immunoassay, detects toxin A, toxin B, or both A and B. It is a same-day assay but is less sensitive than the tissue culture cytotoxicity assay. The tissue culture cytotoxicity assay detects toxin B only. This assay requires technical expertise, is costly, and requires 24 to 48 hours for a final result. It does, however, provide specific and sensitive results for C. difficile-associated disease.
It is important to note that C. difficile toxin is very unstable. The toxin degrades at room temperature and may be undetectable within two hours after collection of a stool specimen. False-negative results occur when specimens are not promptly tested or kept refrigerated until testing can be completed.
C. difficile-associated disease will resolve in one-quarter of antibiotic-related cases within two to three days of discontinuing the problematic antibiotic. The infection can usually be treated with an appropriate course (about ten days) of antibiotics, including metronidazole or vancomycin (administered orally). Following treatment, repeat testing is not recommended if the individual’s symptoms have resolved, due to the fact that many patients remain colonized. In high risk individuals, recurrence of infection or relapse may occur after treatment.