Infectious diarrhea

When a patient presents with acute onset diarrhea, do you test? When you see several patients with vomiting and diarrhea over a short period, do you report to public health?

In BC, summer marks the start of the bacterial and parasitic diarrheal season with an increase in the number of infections and outbreaks associated with Salmonella, E. coli, and Cyclospora. Norovirus and other viruses occur more commonly in the winter months. 

Most enteric pathogens cause diarrhea, abdominal cramps, nausea, or vomiting of several days’ duration. Most infections and intoxications are self-limited; however, some require treatment and may lead to complications. For example, E. coli O157 infections may result in hemolytic-uremic syndrome (8% of cases) and Campylobacter infections may result in Guillain-Barré syndrome (0.1% of cases). Key clinical characteristics such as those summarized in Table 1 can help differentiate between types of enteric intoxications and infections.

The guideline “Infectious Diarrhea—Guideline for Ordering Stool Specimens” can help physicians determine when to request laboratory testing. Key recommendations are summarized in Table 2.

Ova and parasite testing can lead to an overdiagnosis of amebiasis. Only a small proportion of patients are truly infected with Entamoeba histolytica. Frontline laboratories diagnose amebiasis through ova and parasite detection on preserved (formalin fixed) stools; this method cannot differentiate between the pathogenic E. histolytica and the nonpathogenic E. dispar. To confirm diagnosis of E. histolytica, the following can be requested from the BC Public Health Microbiology and Reference Laboratory:
•    ELISA test: Demonstration of E. histolytica on unpreserved stool (paired preserved and unpreserved stool samples are required).
•    E. histolytica serology (cannot differentiate between past or current infections but is useful in the rare cases of invasive disease).
•    Tissue/stool test: Demonstration of E. histolytica that have ingested red blood cells.

The case definition for amebiasis was changed in January 2014 to increase the specificity in public health reporting and investigation (see www.bccdc.ca/dis-cond/a-z/_a/Amebiesis/amebiasisCaseDefinition.htm).

Diarrheal diseases are transmitted via contaminated food or water, from person to person, or via fomites. On average, about one-third of BC cases result from exposure during international travel. Every year, one in eight BC residents gets sick from a domestic foodborne illness. Norovirus, Campylobacter, C. perfringens, Yersinia, and Salmonella cause over 90% of these cases. Waterborne outbreaks have become rare in BC. Some diarrheal pathogens can be transmitted through sexual activities such as oral-anal contact. This occurs most frequently with Shigella, Giardia, and Entamoeba, for which only a small dose is required to cause infection. Sexual transmission of these infections is most commonly seen in men who have sex with men. Diarrhea in this population should be investigated.

Every year there is an average of 19 community-based enteric disease outbreaks investigated in BC. Norovirus and Salmonella together cause 63% of these. The most common outbreak settings are food-service establishments. Among foodborne outbreaks, the most common sources are meat and seafood.

Infectious diarrheal agents are reported by laboratories to public health authorities. However, it may take some time to diagnose sufficient patients to identify an outbreak. In addition, only a small proportion of patients get tested and reported. For every case of Campyobacter, shigatoxin-producing E. coli, and Salmonella infection reported, up to 37, 47, and 49 people, respectively, are infected in the community.

Physicians play an important role in identifying outbreaks in the community. If you are aware that a patient is part of a possible enteric outbreak or you see more than the usual number of patients with vomiting, diarrhea, or both in a short period, please report this to your local health unit or medical health officer for public health investigation. 
—Eleni Galanis, MD, MPH, FRCPC
—Linda Hoang, MD, MHSc, FRCPC
—Marsha Taylor, MSc
—Judy Isaac-Renton, MD, DPH, FRCPC

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This article is the opinion of the BC Centre for Disease Control and has not been peer reviewed by the BCMJ Editorial Board.