A confluence of summertime food preferences and an inexplicable tendency of cattle to have higher levels of E. coli in their guts during warm weather months may partially explain the recent rash of infections among Long Island residents, health experts said Wednesday.

"Across the board, human foodborne illnesses usually spike in summer and you can see that in the ... five-year summaries," of the federal Centers for Disease Control and Prevention that analyze the number of infections season by season nationwide, said Robert Gravani, of Cornell University.

"That's when people are usually outside grilling burgers, taking advantage of the weather," said Gravani, a professor of food sciences.

Studies of cattle herds tell yet another side of the story: E. coli O157:H7, a hardy .microbe that can cause kidney failure in humans, has a definite seasonal prevalence.

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 positive animals declines to less than 5 percent.

Health officials in Suffolk County say the recent spate of E. coli infections may be part of a summertime phenomenon. The number of cases of E. coli infections reported so far this year in Nassau, Suffolk and statewide aren't out of the ordinary.

"What we see in the summer is an increase in cases re.ported," said Dr. Josh Schaffrin, medical director of the regional epidemiology at the New York State Department of Health. "This year, like all other years, we're seeing a good number of cases."

Dr. Anandi Sheth, a medical epidemiologist in the enteric diseases branch at the CDC, said E. coli's seasonality is not surprising.

"There are lots of bacteria that are seasonal," she said. "Sometimes with certain types of salmonella we see it seasonally. But the same can be said for certain viruses. We see more influenza in winter. So there are a multitude of agents that cause infectious diseases that are more prevalent at certain times of the year."

Mindful of the potential harm that E. coli O157H:7 can cause, the meat industry has stepped up efforts to eliminate the potentially deadly pathogen.

"There are specific things that plants do in the slaughtering process to eliminate E. coli from hides," Gravani added.

But in the end, he said, consumers must take steps to protect themselves. He said that following U.S. Department of Agriculture cooking guidelines is the strongest defense against infection. "The recommendation is to cook hamburger to 160-degrees Fahrenheit," he said.

Gravani added that visual observation of meats usually is not sufficient to determine whether a steak or burger is well-cooked, and recommends use of a cook's thermometer to be certain.

Staff writer Chau Lam contributed to this story.
With summer grilling comes E. coli - Newsday.com