Enterotoxigenic E. coli (ETEC) is an underestimated source of domestically acquired illness in the United States, according to researchers.

A study, published in the journal Epidemiology and Infection, looked at ETEC infections reported to the Minnesota Department of Health during 2016 and 2017.

Although travel is a risk factor for ETEC infection, the study found domestically acquired infections made up a substantial proportion of all cases; 68 percent of ETEC patients reported no travel outside the United States in the week before illness onset.

Researchers said it adds to a growing body of evidence indicating that ETEC is an underestimated source of illness in the U.S.

In developed countries, the infection has been associated mostly with traveler’s diarrhea among visitors to endemic developing countries. The main symptom of infection is watery diarrhea that typically lasts three to five days.

Details of infections
In the U.S., an estimated 40,000 cases occur annually, with 55 percent linked to international travel and 45 percent acquired domestically through foodborne transmission, according to a 2011 study in Emerging Infectious Diseases.

Of 244 ETEC cases, the Minnesota public health lab received ETEC-positive stool specimens from clinical laboratories for 222 cases and confirmed the presence of ETEC in 108 of them.

Among all 222 confirmed and probable cases, 52 percent were male. Those who self-reported their race as white accounted for 85 percent of cases, with 11 percent of Hispanic ethnicity. The median age of patients was 44 years, with 15 percent aged under 18 years old.

More confirmed than probable cases reported Hispanic ethnicity. Compared with estimates of the entire Minnesota population, a higher proportion of ETEC cases reported Hispanic ethnicity, and a lower proportion was aged under 18.

Diarrhea was the most common self-reported symptom in almost all of those interviewed, which lasted a median of eight days. Cramps were reported in most cases; less common symptoms included fever, headache, vomiting, and bloody stools. Fifteen percent of people were hospitalized, but nobody died.

International travel data were available for 204 of 244 cases. Sixty-six people reported traveling to another country during the week before illness onset. People went to 41 countries across different regions; Mexico was the most frequent destination accounting for 21 cases followed by the Dominican Republic with eight.

Increased testing and potential sources
Culture-independent diagnostic tests (CIDTs) capable of detecting ETEC have become increasingly prevalent in the last decade.

“No outbreaks were identified during the study period, but it is likely that more outbreaks will be identified in the future as more cases are identified by CIDTs and more states adopt ETEC surveillance,” said researchers.

However, reporting of ETEC-positive stool specimens is not mandatory in most jurisdictions and many cases go undetected with the incidence of infection likely “substantially underestimated”, according to the study.

ETEC was the sixth most frequently reported bacterial enteric pathogen among a subset of CIDT-positive specimens following Campylobacter, enteroaggregative E. coli (EAEC), enteropathogenic E. coli (EPEC), Salmonella, and STEC. It was ahead of Shigella, Yersinia enterocolitica, and Vibrio.

In total, 145 ETEC cases had at least one other reportable enteric pathogen detected. Of these, 59 had at least two such pathogens detected in addition to ETEC, and nine had three or more other pathogens.

Sixty-nine lab-confirmed cases had an additional pathogen co-detected with ETEC, including EAEC 40 times and EPEC on 39 occasions. Among cases who traveled internationally, 60 of 66 had additional co-detected pathogens, compared with 73 of 138 who did not report international travel.

Compared with sporadic, domestically acquired Salmonella patients from the same period, domestic ETEC cases were significantly more likely to report consumption of celery, cucumbers, sesame seeds, citrus fruits other than oranges, and melon other than watermelon or cantaloupe. They were less likely to report contact with animals, eating at restaurants, consumption of spinach, and of lettuce other than iceberg or romaine.