A prolonged outbreak of Salmonella Infantis associated with pork products in central Germany, April-October 2013

Abstract

One of the largest and longest Salmonella outbreaks in Germany within the last 10 years occurred in central Germany in 2013. To identify vehicles of infection, we analysed surveillance data, conducted a case-control study and food traceback. We identified 267 cases infected with Salmonella Infantis with symptom onset between 16 April and 26 October 2013 in four neighbouring federal states. Results of our study indicated that cases were more likely to have eaten raw minced pork from local butcher's shops [odds ratio (OR) 2·5, 95% confidence interval (CI) 1·1-5·8] and have taken gastric acid-reducing or -neutralizing medication (OR 3·8, 95% CI 1·3-13) than controls. The outbreak was traced back to contaminated raw pork products found in different butcher's shops supplied by one slaughterhouse, to pigs at one farm and to an animal feed producer. Characterization of isolates of human, food, animal, feed, and environmental origin by phage-typing and pulsed-field gel electrophoresis confirmed the chain of infection. Insufficient hygiene standards in the slaughterhouse were the most probable cause of the ongoing transmission. We recommend that persons taking gastric acid suppressants should refrain from consuming raw pork products. Improving and maintaining adequate hygiene standards and process controls during slaughter is important to prevent future outbreaks.

Keywords: Epidemiology; Salmonella; foodborne infections; outbreaks; public health.

Fig. 1.

Reported incidence rates of Salmonella Infantis cases per 100 000 inhabitants by region of residence, 16 April–23 October 2013, central Germany (n = 267).

Fig. 2.

Notified Salmonella Infantis cases by onset of disease (n = 253) within the federal states of Thuringia, Lower Saxony, Saxony-Anhalt, and Hesse, April–October 2013, as well as the investigation timeline, measures taken and results.

Fig. 3.

Flow chart of cases and controls enrolled in the case-control study of Thuringia and Lower Saxony between June and September 2013.

Fig. 4.

Flow diagram of the food supply chain. The diagram indicates the number of cases that were connected to different butcher's shops, supplied by one slaughterhouse with pork products. One Salmonella Infantis-positive carcass led to pig farm B and further to feed producer X. The same contaminated feed was supplied to pig farm B and cattle farm A with S. Infantis-infected animals. The colour-coded key indicates the different types of samples that were positive.