Researchers at the University of Minnesota and the University of Nebraska have found that from June through September up to 10 percent to 20 percent of all cattle may test positive for the microbe, which is harmless to cows. In winter, the number of E.coli-positive animals declines to less than 5 percent.

Dr. Robert Gravani of Cornell University acknowledged that summertime means more E. coli outbreaks, and pointed out that consumers grilling more hamburgers is not the only cause, reports Newsday.