Michael HOEHLE

Challenges for statistical modelling during the STEC/HUS outbreak in Germany, 2011 

Abstract: During May-July 2011, Germany was confronted with a large outbreak of gastrointestinal disease caused by Shiga toxin-producing Escherichia coli (STEC) O104:H4 associated with sprouts. A total of 2,987 cases of diarrhoea without the haemolytic uremic syndrome (HUS) complication and 855 cases of HUS were attributable to the outbreak, making this one of the largest STEC outbreaks ever reported. In my talk, I will focus on a number of challenges this outbreak induced for statistical modelling, especially, latency periods and their consequences. This includes the latency period between exposure to the disease and onset of diarrhoea in cases and the inherent reporting delay present in any public health surveillance system. Based on an incubation-time estimation, non-parametric back projection was used to retrospectively back-project the daily number of diarrhoea onsets of STEC and HUS cases. Furthermore, a nowcasting procedure was used to extrapolate from observed to actual counts by adjusting for reporting delay. Altogether, this allowed us to assess epidemic trends during the outbreak and to identify the time interval, where the majority of contaminated food was consumed. If time permits, I will also briefly touch upon challenges in classical case-control methodology for source identification, e.g. estimating odds ratios in 2x2 tables with zero cells and the computation of odds ratios in the light of exposure misclassification bias.

Mis à jour le 06/02/2014