Contaminated food sources continue to be the most common source of outbreaks of Escherichia coli O157 (E. coli) in the United States, according to the most recent data published on these infections released by the Centers for Disease Control and Prevention.
There were 390 E. coli-related outbreaks, which included 4,928 illnesses, 1,272 hospitalizations, and 33 deaths from 2003 through 2012.1
The report notes 65% of outbreaks were due to food, and 10% were due to person-to-person contact. Another 10% of cases resulted from contact with animals and 15% from contaminated water. Eleven percent of cases had a ‘different or unknown mode of transmission.’
Contaminated Food Most Common Source of E. Coli Outbreaks
“Our study indicates that contaminated food continues to be the most common source of E. coli outbreaks in the United States, followed by contact with animals and person-to-person transmission,” said Katherine Heiman, MPH, epidemiologist in the division of foodborne, waterborne, and environmental diseases at the CDC’s National Center for Emerging and Zoonotic Infectious Diseases in Atlanta, Georgia.
The data highlight that E. coli outbreaks were most commonly caused by ground beef, but also was caused by leafy vegetables and unpasteurized dairy products. E. coli outbreaks occurred most frequently in the northern United States during the summer months.
Severity of Outbreaks Varied by Mode of Transmission
In terms of severity of outbreaks, Heiman and colleagues evaluated rates of hospitalization, rates of hemolytic uremic syndrome, and number of deaths among ill persons linked to an outbreak.
“We found that outbreaks that were linked to foods that are typically consumed raw – including produce – were more severe. Outbreaks caused by contact with animals also tended to be more severe,” said Heiman. “We don’t know the underlying reasons for these differences, but possible explanations include differences in the virulence of the strains causing infection or different susceptibilities of adults versus children to infection.”
Surveillance and Awareness Improving E. Coli Detection
The identification of E. coli outbreaks has increased over the last 20 years, and it’s likely this is attributable to improved surveillance and awareness.
“Surveillance for E. coli infections and outbreaks has substantially improved in the past two decades. For example, PulseNet, the national molecular subtyping network, detects more outbreaks earlier. Public health agencies are getting better at investigating outbreaks, and reporting of all outbreak causes has allowed our surveillance systems to systematically capture more types of outbreaks than before,” said Heiman.
The findings in this report are very similar to previous findings. However, the investigators did find that contaminated food was responsible for a larger percent of outbreaks during our study.
“We think this might be a result of improved outbreak detection, investigation, and reporting. Food items that had never been linked to an outbreak of E. coli infections previously – including cookie dough, hazelnuts, strawberries, and salsa – were identified by local, state, and federal health officials, underscoring the importance of continued detection and investigation of E. coli outbreaks,” says Heiman.
Further Steps to Reduce E. Coli Outbreaks
According to Heiman, more can be done to reduce the number of E. coli infections in the United States, such as finding ways to eliminate E. coli bacteria from beef and researching ways to reduce and prevent contamination of raw produce items, like lettuce.
Heiman recommends that consumers cook ground beef and beef steaks to a temperature of at least 160 degrees Fahrenheit and use a meat thermometer to check the temperature. In addition, it is also important to wash hands thoroughly after handling raw beef or raw dairy products, and after touching animals or their environment. Do not eat unpasteurized or and thoroughly wash hands using soap and water. Heiman also recommends following four steps for food safety: clean, separate, cook, and chill.
Overall, according to L. Hannah Gould, PhD, of the Division of Foodborne, Waterborne, and Environmental Diseases in National Center for Emerging and Zoonotic Infectious Diseases of the Centers for Disease Control and Prevention in Atlanta, Georgia, “Analyses like this one help to highlight gaps in the food safety system and identify prevention needs. With enhancements to surveillance, we are identifying and solving more outbreaks, and learning about new foods that cause them.”
Medically reviewed by Pat F. Bass III, MD, MS, MPH