Using an outbreak to study the sensitivity of the surveillance of enterohaemorrhagic Escherichia coli and other enteropathic Escherichia coli in Bavaria, Germany, January to October 2011

Following an outbreak of enterohaemorrhagic Escherichia coli (EHEC) in Germany 2011, we observed increases in EHEC and non-EHEC E. coli cases in Bavaria. We compared the demographic, clinical and laboratory features of the cases reported during the outbreak period, but not related to the outbreak, to the cases reported before and after. The number of EHEC and non-EHEC E. coli cases notified per week during the outbreak was fivefold and twofold higher respectively, compared to previous years. EHEC cases notified during the outbreak were more often reported with bloody diarrhoea, and less often with unspecified diarrhoea, compared to the other periods. They were more often hospitalised during the outbreak and the following period compared to the period before. Their median age (26.5 years, range: 0-90) was higher compared to before (14.5 years, range: 0-94) and after (5 years, range: 0-81). The median age of non-EHEC E. coli cases notified during the outbreak period (18 years, range 0-88) was also higher than before and after (2 years, p<0.001). The surveillance system likely underestimates the incidence of both EHEC and non-EHEC E. coli cases, especially among adults, and overestimates the proportion of severe EHEC cases. Testing all stool samples from patients with diarrhoea for enteropathic E. coli should be considered. .