Better reporting is at least partially responsible for the increase in O157? Well, that's not it.
Although there may be increase awareness, there is no evidence to indicate increased ordering of stool cultures by MDs. If the increase in E. coli O157 was a result of increased testing, we would have seen an increase in all enteric bacterial pathogens. O157 has been reportable in all states for a while, so there is no reason to believe that the same number is being
identified, but a higher proportion reported to the health dept. Additionally, more and more clinical labs are switching to Shiga toxin testing using non-culture methods. Most of the non-culture methods used by clinical laboratories do not differentiate between O157 and non-O157 STEC. Very few states (maybe only 1) have added submission of the broth resulting from the non-culture method to the state lab for culture, serotyping and subtyping/PFGE. since many of those cases are being identified as ST
positive, without the actual culture, they are not counted as O157 by state health dept or CDC (they are STEC, O157=unknown). Therefore, the changes in
laboratory practices may be resulting in undercounting O157 compared to previous years. Besides, increased reporting does not explain the increase in USDA positive samples in routine testing and recalls due to those positive test results. So,as nice as it would be to blame it on increased reporting, that's not it.

1. The prevalence in cattle appears to be increasing if you look at the literature (and unpublished data), but in my mind most of this is due to improved laboratory and sampling methods. Still, it has surprised me how easily we recover E. coli O157 in our state (which previously discouraged testing even in research, so we have no baseline). What if it is related to more than testing methods?

2. Couldn't some of this increase be from consumers and food handlers developing a false sense of security over time following a perceived reduction in risk (and less media coverage/outreach)? We see this a lot in public health--not a good analogy, but you get something like HIV rates down, and in a few years see them climb back up as the perception of risk goes down. Its a cycle. Of course, with food safety, the producers can break the cycle.

In this context, I believe their are a number of confounding factors. However, I don't believe the increase in E. coli cases is a product of simply better reporting. Your list of factors is good food for thought- no pun intended.