E.coli outbreaks grow and beef is top cause

US-based outbreaks continue to be caused mostly by contaminated food, especially beef.

Researchers identified 390 outbreaks, which included 4,928 illnesses, 1,272 hospitalizations, and 33 deaths.

Transmission was through food (255 outbreaks, 65%), person-to-person contact (10%), indirect or direct contact with animals (10%), and water (4%); 42 (11%) had a different or unknown mode of transmission.

Source of outbreaks​

Beef and leafy vegetables were the source of >25% of all reported E. coli outbreaks and of >40% of related illnesses.

Outbreaks attributed to foods generally consumed raw caused higher hospitalization rates than those attributed to foods generally consumed cooked (35% vs. 28%).

Foodborne disease outbreaks caused the most illnesses (3,667, 74%), hospitalizations (1,035), physician-diagnosed HUS cases (209), and deaths (25).

They summarized outbreaks of E. coli O157 in the US during 2003–2012, including demographic characteristics of patients and epidemiologic findings by transmission mode and food category.

The most common reservoir is cattle, and ground beef is the most frequently identified vehicle of transmission to humans. 

Changes over time​

Two periods, 2003–2007 and 2008–2012, were evaluated to assess changes over time.

During 2009–2012, when data for culture-confirmed infections were collected for all outbreaks, transmission were unknown modes (76%), foodborne (69%), person-to-person (62%), and animal contact (40%).

The median annual number of foodborne disease outbreaks did not change, although dairy (11 vs. 5) and fruits (5 vs. 2) more than doubled.

Of 255 foodborne disease outbreak reports, 170 (67%) implicated a specific food, of which 141 (83%) could be classified into a single category.

These were beef (78 outbreaks, 55%), leafy vegetables (21%), dairy (11%), fruits (4%), other meats (5%), sprouts (2%), nuts (1%), and poultry (1%).

Outbreaks attributed to leafy vegetables, dairy products, fruits, and other meats were more severe than those from beef for reasons including strain virulence and patient age and sex.

More outbreaks were reported during 2003–2012 than the previous 20 years although illnesses decreased.

“Contaminated food was responsible for a larger percent of outbreaks during our study (65% vs. 52%), and the percent attributed to another or unknown mode decreased (10% vs. 21%).​

“Among foodborne disease outbreaks, the percentage caused by ​E. coli​ O157 in beef decreased (31% vs. 47%), and among outbreaks associated with beef, the percentage linked to ground beef decreased (21% vs. 41%), whereas the percentage associated with other types of beef increased (9% vs. 6%).”​

E. coli O157 outbreaks occurred year-round; however, nearly half were during July–September.

Beef-associated outbreaks occurred most often in July (21 outbreaks, 27%), and leafy vegetable-associated outbreaks in September.

Researchers used the Foodborne Disease Outbreak Surveillance System (FDOSS) during 2003–2012; the Waterborne Disease Outbreak Surveillance System (WBDOSS) during 2003–2010 and the National Outbreak Reporting System (NORS) for outbreaks facilitated by transmission between persons, animal contact, environmental contamination, or unknown transmission mode during 2009–2012.

They also used the Centers for Disease Control and Prevention of person-to-person and animal contact–associated outbreaks during 2003–2008; and PubMed using search terms: Escherichia coli O157 outbreak, STEC O157 outbreak, Escherichia coli O157, STEC O157, and O157. 

Source: Emerging Infectious Diseases Volume 21, Number 8—August 2015

“E​​.coli​ O157 Outbreaks in the United States, 2003–2012​​”

Online doi: 10.3201/eid2108.141364

Authors: Katherine E. Heiman, Rajal K. Mody, Shacara D. Johnson, Patricia M. Griffin, and L. Hannah Gould