In nearly every E. coli outbreak-situation, secondary E. coli cases, or cases in which a person exposed directly to the source of the outbreak passes their infection to another person, occur. The method of transmission for these person-to-person cases of E. coli is fecal-oral, and is particularly common among infants and young children who have not yet developed hygienic practices conducive to stopping the spread of E. coli. Other person-to-person transmission of E. coli has been known to occur between infected individuals and their caregivers, and between infected food handlers and people who consume the food they prepare.
A person who has become infected with E. coli can shed bacteria in their stool for up to three weeks, and is infectious until E. coli can no longer be isolated from their stool. Proper hand washing reduces the risk of transmission from person-to-person, and is essential for anyone recovering from an E. coli infection, as well as for people caring for individuals with E. coli infection and those changing the diapers of infected children.
Occasionally, individuals with E. coli infection are asymptomatic, or do not display symptoms of E. coli infection. Person-to-person transmission within a family in which the primarily infected person is asymptomatic is well-documented. For example, in the Jack in the Box outbreak 501 E. coli cases were reported. Three hundred ninety-eight (78%) met the definition of a primary case, 48 (10%) were secondary cases, and 55 (11%) could not be classified as primary or secondary.*
In 1998, an E. coli O157:H7 outbreak was traced to ground beef served in a taco lunch at Finley Elementary School in Southeastern Washington State. The Washington Department of Health (WDOH) and Benton-Franklin Health District investigated the E. coli outbreak, and identified nine confirmed and two probable E. coli cases among students who attended Finley Elementary. Epidemiologists determined that a two-year-old child who did not attend the school had also become ill with the outbreak strain of E. coli O157:H7 through person-to-person contact with a sibling and other children who attended the school and had eaten the taco lunch. The two-year-old child developed hemolytic uremic syndrome (HUS), and was the most severely injured victim of the E. coli outbreak. See Finley Elementary School and Northern States Beef E. coliLawsuits and Litigation.
*B. Bell, A Multistate Outbreak of Escherichia coli O157:H7-Associated Bloody Diarrhea and Hemolytic Uremic Syndrome From Hamburgers: The Washington Experience, JAMA, 272/17, at 1351 (November 2, 1994).