Shiga toxin-producing Escherichia coli (STEC) has long been considered as a major cause of bloody diarrhea, and a life-threatening condition named hemolytic uremic syndrome (HUS) in humans worldwide. Historically, the serotype O157:H7 STEC caused two large outbreaks in the United States and Japan in 1993 and 1996, respectively.1 This serotype has been frequently reported as a cause of diarrhea and HUS and therefore is the most investigated serotype worldwide.2 A brief search shows numerous reports of O157 E. coli in Iran among isolates from different animal species and occasionally humans–albeit not associated with severe cases. For instance, O157 E. coli has been reported in humans (uncomplicated diarrhea), sheep, goats, cattle, water buffalos and camels in Iran in recent years.3-8 At the same time, to the best of our knowledge, there has not been any outbreak reported in association with this serotype in humans in Iran.9,10 Accordingly, we can draw two hypotheses explaining this. First, it can be resulted from a lack of comprehensive monitoring that might need revising routine diagnostic algorithms, and the second could be the presence of less virulent clones of O157 E. coli circulating in Iran. With the context of the later hypothesis, we can explain this in brief as our current knowledge on virulence of this serotype increased substantially in the genomics era.

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