Epidemiology

Escherichia coli is generally a commensal organism that makes up a significant portion of normal fecal microenvironment in humans. Pathogenic forms of E coli are associated with extra-intestinal infections (such as urinary tract infections and pneumonia).

The epidemiology and route of acquisition of the different forms of E coli that cause enteric infections vary according to pathogenic subtypes. As with other intestinal pathogens, all ages, races, and sexes are at risk following oral contamination. Older people, infants, and people who are immunocompromised are more susceptible to infection, prolonged infectious course, and secondary complications. Due to the variability in testing and reporting of bacterial diarrheal illnesses as a result of geographic and economic differences, the true incidence of intestinal infections from the various forms of E coli is unknown.[5]

Enteropathogenic E coli (EPEC) is a common cause of infant diarrheal infections.[6] Outbreaks at child care centers have been reported.[7]

Enterotoxigenic E coli (ETEC) is the leading cause of community-acquired diarrhea (approximately 14% of cases) as well as the leading cause of traveler's diarrhea, accounting for about 30% of cases.​[8] The Global Burden of Disease study found that, in 2016, ETEC was the eighth leading cause of diarrhea mortality in all age groups, accounting for 51,186 deaths (approximately 3.2% of diarrhea deaths).[9]

Enteroaggregative E coli (EAEC) is the second most common diarrheal pathogen in travelers to Latin America.[8] Both EPEC and EAEC are more common in developing countries, with EPEC accounting for 5% to 20% of pediatric diarrheal illnesses in this setting.[10]

Enteroinvasive E coli (EIEC) appears to be a less common cause of diarrheal illness compared with other forms of pathologic E coli. This group of E coli shares common features with Shigella.

Enterohemorrhagic E coli (EHEC), which is also referred to as Shiga toxin-producing E coli (STEC), causes more than 265,000 infections each year in the US.[11]​ These infections are usually classified as O157 and non-O157. E coliO157 is responsible for approximately 36% of EHEC infections.[12] The incidence of EHEC is likely underestimated, as not all patients will seek medical attention, stool samples are infrequently tested, and non-O157 EHEC testing is limited to only a subset of laboratories. One study has shown that the incidences of STEC, Yersinia, Vibrio, and Cyclospora infections were higher in 2022 than those reported from 2016 to 2018. The incidences of Campylobacter, Salmonella, Shigella, and Listeria infections were similar for these time periods.[13]

There are more than 73,000 illnesses caused by E coli O157:H7 reported in the US each year.[14] Intermittent large-scale outbreaks lead to significant variability in incidence.[14][15]​ Most outbreaks are related to consumption of undercooked meat. According to a UK Health Security Agency report, 402 cases of STEC were reported in England and Wales in 2020.[16]​ The number of E coli outbreaks reported to the CDC has declined since peaking in 2005.[14][15]​ In 2018, the largest US outbreak of E coli O157:H7 in more than 10 years was reported, the source of which was romaine lettuce from the Yuma growing region.[15] A total of 210 people from 36 states were infected, and five deaths were reported.[15]

Diffusely adherent E coli (DAEC) is a less common cause of infectious diarrhea, and is more commonly associated with children and people traveling in North Africa, Mexico, or South America. Studies have suggested it accounts for 8% to 14% cases of traveler's diarrhea.[17]

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