The Centers for Disease Control and Prevention (CDC) has released a summary of E. coli O157 outbreaks in the United States in recent years caused by food, person-to-person contact, contact with animals, and water. As in previous reports, the analysis of data from multiple federal surveillance systems, reports to CDC, and searches of PubMed found that food was the major mode of transmission for E. coli O157 outbreaks. 2003 and 2012, there were 390 outbreaks of E. coli O157 from all sources. These included 4,928 illnesses, 1,272 hospitalizations, and 33 deaths. There were also 299 physician-diagnosed cases of hemolytic uremic syndrome (HUS). The size of the outbreaks ranged from 2 to 238 cases, but the median size was 6 illnesses. Most of the decade’s outbreaks (65 percent) were connected to food. The rest were caused by person-to-person contact, indirect or direct contact with animals, and water. Outbreaks by Food Category Of the 255 foodborne disease outbreak reports, 141 implicated a specific food that could be classified into a single category. Outbreaks attributed to foods generally consumed raw caused higher hospitalization rates than those attributed to foods generally consumed after being cooked. Beef was linked to 78 outbreaks, leafy vegetables to 29, and dairy to 16. The additional categories were other meats, fruits, sprouts, nuts and poultry. The types of beef implicated were ground beef and steak that had been mechanically tenderized. Thirteen of the outbreaks attributed to dairy were linked to unpasteurized milk, and the other three were linked to cheese made from unpasteurized milk. Some of the new food vehicles identified in this period included raw, prepackaged cookie dough, hazelnuts, strawberries and salsa. The median annual number of foodborne disease outbreaks did not change between 2003-2007 and 2008-2012, but the number attributed to dairy and fruits more than doubled. Heiman-EcoliTable_700 Outbreaks by Season and Location All of the E. coli O157 outbreaks occurred year-round, but nearly half occurred between July and September. Looking at foodborne outbreaks specifically, those associated with leafy vegetables were more common in the fall. This could be the result of summertime application of irrigation water to seedlings, soil amendments, or fertilizers that might contain more E. coli O157 organisms than other seasons. “Therefore, leafy vegetables harvested during fall might be more likely to become contaminated than those grown at other times,” the researchers wrote. The rate of foodborne outbreaks were highest in Northern states, although the reason for this is unknown, and most waterborne E. coli outbreaks occurred in states bordering the Mississippi River. Of the 15 waterborne disease outbreaks, 10 were attributed to recreational water, three to drinking water, and one possibly to wastewater. The water source was unknown for the remaining outbreak. Foodborne Illness Patients Foodborne disease occurred among all age groups. Only 8 percent of cases were children younger than 5 years old, but about 25 percent of those sickened in the dairy outbreaks were younger than the age of 5. And the proportion of female patients was highest in outbreaks attributed to fruits and leafy vegetables, but the lowest was in outbreaks attributed to meats other than beef. Of the 33 deaths reported, 25 were from a foodborne source and occurred most commonly in outbreaks attributed to leafy vegetables. The researchers wrote that higher hospitalization rates in outbreaks attributed to certain foods might be influenced by the patients’ gender. The researchers suggest that people can protect themselves through proper handling of raw beef, by cooking non-intact beef products such as ground beef and mechanically tenderized steak to internal temperatures of at least 160 degrees F, and by thorough hand-washing after contact with animals or their environment. “Clearly labeling mechanically tenderized beef might help consumers make safer choices,” they wrote. “Pasteurizing dairy products and fruit juices is recommended. Further research is needed to identify interventions to reduce the risk of illness caused by consumption of raw produce.”

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