The decrease in the proportion of PT21/28 and increase in PT32 were not mirrored by data on the human cases. Such results may be a reflection of the proposed heterogeneity in transmission [39]. In addition, PT32 may either be less stable in the environment than PT21/28 and/or less virulent to humans [41]. In this paper we have highlighted the importance

of cattle as the primary source of human E. coli O157 infection. Cattle are the major reservoirs of E. coli O157 [54], they carry it asymptomatically in their intestines and excrete it in their faeces. Excretion rates for some animals (i.e. super-shedders) can be high (≥104 colony forming units (CFU) per gram of faeces) [34]. The potentially high excretion rate, longevity of E. coli O157 in pasture and soil [55] and the low infectious dose for human infection [53]

buy Poziotinib mean that the environment is an important source of infection for humans. Comparison of 90 published E. coli O157 outbreaks meeting certain criteria (eg secondary cases were identifiable) from 9 countries [56] has identified exposure to contaminated food (54%) and environmental sources (including AZD3965 animal contact and water contamination) (17%) as the most frequently reported primary modes of transmission [56]. Analysis of general outbreaks (ie outbreaks involving the members of more than one household, or of institutions) of E. coli O157 infection in Scotland associated with either meat or dairy foods, or with environmental transmission (including direct contact with animals and their faeces and contaminated water supplies) showed that approximately 40% of these outbreaks were associated with foodborne transmission, 54% with environmental transmission and 6% with both modes of transmission [57]. However, most infections in Scotland are sporadic or single household cases, and not part of general outbreaks. Contact with livestock faeces was the risk factor most strongly associated with

sporadic MRIP infection [10]. This further highlights the cattle and the environment as an important sources of E. coli O157 infections in humans. It remains to be seen whether the decline in the mean prevalence of E. coli O157 cattle shedding observed between the SEERAD and IPRAVE surveys continues, but there are precedents among other members of the Enterobacteriaceae family e.g. Salmonella [58] to suggest that this is possible. Despite observing declines in the number of human E. coli O157 cases over the time periods equivalent to the two cattle surveys, incidence rates, at least from 1998, do not seem to suggest a downward trend (Figure 4). Although these data were not generated by our study, examination of the reported rate of E. coli O157 infection per 100,000 population in Scotland shows that from 1998 to 2007 there was no change in the reported national rate of human cases (slope not significantly 3-deazaneplanocin A different from zero, P = 0.65) (Figure 4).