Bad Bug Book:
Foodborne Pathogenic Microorganisms and Natural Toxins Handbook
Enterotoxigenic Escherichia coli
Enterotoxigenic Escherichia coli (ETEC)
Currently, there are four recognized classes of enterovirulent E. coli (collectively referred to as the EEC group) that cause gastroenteritis in humans. Among these are the enterotoxigenic (ETEC) strains. They comprise a relatively small proportion of the species and have been etiologically associated with diarrheal illness of all age groups from diverse global locations. The organism frequently causes diarrhea in infants in less developed countries and in visitors there from industrialized countries. The etiology of this cholera-like illness has been recognized for about 20 years.
Gastroenteritis is the common name of the illness caused by ETEC, although travelers' diarrhea is a frequent sobriquet.
The most frequent clinical syndrome of infection includes watery diarrhea, abdominal cramps, low-grade fever, nausea and malaise.
Infective dose--Volunteer feeding studies indicate that a relatively large dose (100 million to 10 billion bacteria) of enterotoxigenic E. coli is probably necessary to establish colonization of the small intestine, where these organisms proliferate and produce toxins which induce fluid secretion. With high infective dose, diarrhea can be induced within 24 hours. Infants may require fewer organisms for infection to be established.
During the acute phase of infection, large numbers of enterotoxigenic cells are excreted in feces. These strains are differentiated from nontoxigenic E. coli present in the bowel by a variety of in vitro immunochemical, tissue culture, or gene probe tests designed to detect either the toxins or genes that encode for these toxins. The diagnosis can be completed in about 3 days.
ETEC is not considered a serious foodborne disease hazard in countries having high sanitary standards and practices. Contamination of water with human sewage may lead to contamination of foods. Infected food handlers may also contaminate foods. These organisms are infrequently isolated from dairy products such as semi-soft cheeses.
Only four outbreaks in the U.S. have been documented, one resulting from consumption of water contaminated with human sewage, another from consumption of Mexican food prepared by an infected food handler. In two others, one in a hospital cafeteria and one aboard a cruise ship, food was the probable cause. The disease among travelers to foreign countries, however, is common.
The disease is usually self-limiting. In infants or debilitated elderly persons, appropriate electrolyte replacement therapy may be necessary.
Infants and travelers to underdeveloped countries are most at-risk of infection.
With the availability of a gene probe method, foods can be analyzed directly for the presence of enterotoxigenic E. coli, and the analysis can be completed in about 3 days. Alternative methods which involve enrichment and plating of samples for isolation of E. coli and their subsequent confirmation as toxigenic strains by conventional toxin assays may take at least 7 days.
For more information on recent outbreaks see the Morbidity and Mortality Weekly Reports from CDC.