Do you think there is a higher risk at 1,200 feet or less in either riparian or rangeland close to a leafy green field? Or is 30 ft ok?
Our study was not designed to compare STEC risk at specific setback distances from riparian or rangeland areas. Although STEC detection in field soils was generally low, we did observe somewhat higher frequency of STEC detection in soil in closer proximity to riparian areas especially during or following flooding events.
Does the emergence of similar strains in locations that are far apart (50-70 miles) from each other mean they are somehow connected or come from the same source…? Why is this finding so significant?
The detection of highly related STEC strains across different sample matrices, locations, and time periods suggests these strains may be broadly distributed in the environment. However, we cannot determine from these data whether the detections were directly connected or originated from one or more independent sources. It is also likely that additional positive locations and sample matrices existed beyond those sampled and identified in the study.
For riparian risk, what is the believed mechanism that the pathogens move into the fields? Is higher correlation of STEC in soil near riparian habitat thought to be associated with wildlife utilizing these areas as habitat or the assumption that STEC utilizes surface water for movement?
Cropland can be at higher risk of being flooded when adjacent to riparian areas that flank rivers, streams, and seasonal or ephemeral creeks. Flooding was associated with increased STEC detection in soil from impacted fields. In addition, riparian areas can provide habitat for wildlife including food, shelter, and water. Movement of wildlife between riparian habitat and cropland may increase the likelihood of fecal deposition within fields.
How are STEC strains moving from one place to another?
This study was not designed to directly determine how STEC strains move between locations. However, the findings suggest that multiple environmental pathways could contribute to dissemination, including water movement, wildlife activity, and possibly windborne dust. Additional factors not evaluated in this study may also contribute to STEC movement in agricultural environments.
How might we expect non-riparian non-crop vegetation to effect foodborne pathogen incidence? Is higher correlation of STEC in soil near riparian habitat thought to be associated with wildlife utilizing these areas as habitat or the assumption that STEC utilizes surface water for movement?
Non-riparian vegetation adjacent to cropland may influence local wildlife activity and environmental conditions that could affect pathogen movement. For example, less-managed vegetation such as hedgerows, grassland, brushy, or woody areas can provide habitat for wildlife species that may move between these areas and cropland. In addition, runoff during heavy rainfall could transport microorganisms across the landscape and into produce fields.
However, this study was not designed to directly evaluate how non-riparian vegetation affects foodborne pathogen incidence in crops.
In the longitudinal study, did positive detections tend to appear as isolated events or as clusters within certain time windows or ranches?
Some of the STEC detections occurred as clusters of highly related strains that were isolated from various sample matrices and multiple locations. However, there were also instances where STEC was detected from a single sample matrix or a limited number of locations suggesting more isolated events.
Why was E. coli O157:H7 concentrated on? Because it was found in prior outbreaks or because it severely affects humans?
We focused on E. coli O157 because it has been linked to multiple outbreaks associated with leafy greens and other produce commodities. In addition, E. coli O157 is an important human pathogen associated with severe illness, including hemolytic uremic syndrome (HUS), which can lead to kidney failure. Data regarding other E. coli serotypes and other pathogens of clinical significance were collected and are currently being analyzed.
Why wasn't produce sampling included in this study?
Produce sampling was not included in this study because participating farms agreed to environmental sampling only under the terms of the collaboration. These agreements were established to support voluntary industry participation while maintaining confidentiality and minimizing disruption to commercial operations.