to the editor: Upon reading the article on Escherichia coli,¹ I was a bit surprised when the authors stated, “For unknown reasons, the rate of infection follows a seasonal pattern, with a peak incidence from June through September.”

Out here in the Midwest, a lot of folks cook out from June through September. Not surprisingly, many of them cook hamburgers, a wonderful reservoir for E. coli. Since folks at cookouts tend to be impatient, many of them eat hamburger meat that is undercooked. This is, to my simplistic view, a logical explanation for the seasonal peak from June through September.

in reply: We appreciate Dr. Walbroehl's comments on our article. The importance of undercooked hamburgers in the epidemiology for E. coli O157:H7 infection is well-described in the literature and has been referred to as “barbecue syndrome.”¹ This association was actually noted two paragraphs after the phrase that Dr. Walbroehl mentioned; it was also noted in the patient information handout accompanying the article.²

We believe that the epidemiology of E. coli O157:H7 is very important. However, little is known about the actual risk factors. The observation regarding cookouts has been tested in a large and well-documented epidemiologic study,¹ and there was no statistical significance noted with barbecued hamburgers. Although there are studies explaining the epidemiology of E. coli O157:H7-associated gastroenteritis, it is still not fully explained why this infection peaks during the summer.^1,3–5 Also, it was recently noted that the “seasonal variation of E. coli O157:H7 infection may reflect the ecology of the organism, variation in the consumption of ground beef or some other factor.”⁶

More studies are needed to evaluate the seasonal pattern of this disease.