Reviewer 3's Review (Benedicte Lafay)

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The manuscript presents data obtained in the course of several investigations dealing with Escherichia coli O157:H7 occurrence in the environment. E. coli O157:H7 is responsible for severe foodborne pathologies in humans and it is thus of importance to understand its ecology in order to assess the epidemiological risk associated with environmental contamination.

Whereas a lot of work has obviously been involved in producing the results, the manuscript unfortunately fails in providing a coherent story. Most critically, little effort seems to have been put into organizing the various data and relevant facts, analyzing them together as well as in a general context, and providing a (hypo)synthesis.

It actually looks as though the paper was built from the compilation of separate reports, each dealing with a different aspect of the study, and that the only trace of an attempt at presenting them into a larger story is that results and partial conclusions are scrambled in and scattered across all parts of the manuscript (and at times repeated). The reader is then left to extract and organize the relevant data -and to imagine those missing- to be able to comprehend:

- what the aim of the paper really was : investigating the epidemiological risk associated to in-field contamination, survival and spread of E. coli O157:H7, in contrast to what the title and abstract suggest and what is stated at the end of the introduction (they appear essentially to correspond to the molecular typing part of the study) ;

- how the survey was conceived and conducted : a paragraph describing the sampling strategy and a map presenting the locations of all -including the farms/ranches- sampled sites are critically missing. A different presentation of the results (for example, the organisation of Table S1 according to the spatial and temporal sampling source, the use of histogrammes, the removal of Figure 1 which is not cited in the text) may be considered ;

- what the conclusions may be and how they compare to what is already know on the subject. As reported here, the whole story cannot be made out without a major imagination and data processing (and rewriting) effort from the reader.
It is thus unfortunately currently difficult to grasp the real impact of the study.

Possibly because of this, the manuscript is overly long. A more concise and focused presentation would most likely contribute better to emphasize the major findings.

Another concern is that at least some of the results have been published elsewhere (although apparently mostly in the form of administrative reports, e.g., references 9 and 41, but see also the citation on page 32).

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N.B. These are the general comments made by the reviewer when reviewing this paper in light of which the manuscript was revised. Specific points addressed during revision of the paper are not shown.